oEPA
United States
Environmental Protection
Agency
Environmental Monitoring
and Support Laboratory
P.O. Box 15027
Las Vegas NV 89114
EPA-600/7-78-188
September 1978
Research and Development
Geothermal Environmental
Impact Assessment:
Baseline Data for Four
Geothermal Areas in the
United States
Interagency
Energy-Environment
Research
and Development
Program Report
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad categories
were established to facilitate further development and application of environmental
technology. Elimination of traditional grouping was consciously planned to foster
technology transfer and a maximum interface in related fields. The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7 Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the INTERAGENCY ENERGY—ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from the effort
funded under the 17-agency Federal Energy/Environment Research and Development
Program. These studies relate to EPA'S mission to protect the public health and welfare
from adverse effects of pollutants associated with energy systems. The goal of the Pro-
gram is to assure the rapid development of domestic energy supplies in an environ-
mentally-compatible manner by providing the necessary environmental data and
control technology. Investigations include analyses of the transport of energy-related
pollutants and their health and ecological effects; assessments of, and development of,
control technologies for energy systems; and integrated assessments of a wide range
of energy-related environmental issues.
This document is available to the public through the National Technical Information
Service, Springfield, Virginia 22161
-------
EPA-600/7-78-188
September 1978
GEOTHERMAL ENVIRONMENTAL IMPACT ASSESSMENT
Baseline Data for Four Geothermal Areas
in the United States
by
Geonomics, Inc.
Berkeley, California 94703
Contract No. 68-03-2468
Project Officer
Donald B. Gilmore
Monitoring Systems Research and Development Division
Environmental Monitoring and Support Laboratory
Las Vegas, Nevada 89114
ENVIRONMENTAL MONITORING AND SUPPORT LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
LAS VEGAS, NEVADA 89114
-------
DISCLAIMER
This report has been reviewed by the Environmental Moni-
toring and Support Laboratory, Las Vegas, U.S. Environmental
Protection Agency, and approved for publication. Approval does
not signify that the contents necessarily reflect the views and
policies of the U.S. Environmental Protection Agency, nor does
mention of trade names or commercial products constitute en-
dorsement or recommendation for use.
-------
FOREWORD
Protection of the environment requires effective regulatory
aptions which are based on sound technical and scientific infor-
m£tion. This information must include the quantitative descrip-
tion and linking of pollutant sources, transport mechanisms, in-
teractions, and resulting effects on man and his environment.
Because of the complexities involved, assessment of specific pol-
lutants in the environment requires a total systems approach
which transcends the media of air, water, and land. The Environ-
mental Monitoring and Support Laboratory-Las Vegas contributes
to the formation and enhancement of a sound monitoring data base
for exposure assessment through programs designed to:
• develop and optimize systems and strategies for monitor-
ing pollutants and their impact on the environment
• demonstrate new monitoring systems and technologies by
applying them to fulfill special monitoring needs of the
Agency's operating programs.
This report is the first in a series of five reports cover-
ing the following subjects:
• baseline geotechnical data for four geothermal areas in
the United States
• subsurface environmental assessment of geothermal develop-
ment
• a guide for decision-makers
• a pollution control technology guidance manual, and
• a groundwater monitoring methodology for geothermal
developments.
The first two reports cover the baseline data necessary for
the development of the last report. It will contain the strategy
for monitoring change in groundwater quality as a result of any
geothermal resource development, conversion and waste disposal.
The third report will be a guideline for those persons
111
-------
.charged with responsibility for issuing permits for geother-
mal exploration, development, conversion and waste disposal.
Report 4 will cover justification of the need, by way of
regulatory or anticipated regulatory requirements, for con-
trol of constituents of raw wastes and a description of waste
control technology alternatives.
For further information on these reports, contact the
Monitoring Systems Research and Development Division at the
Environmental Monitoring and Support Laboratory, Las Vegas,
Nevada.
George B. Morgan
Director
.Environmental Monitoring and Support Laboratory
Las Vegas, Nevada
IV
-------
ABSTRACT
This report presents a compilation and technical assessment
of the existing data on climate, geology, hydrology, water che-
mistry and seismicity for four geothermal areas in the United
Spates : Imperial Valley and The Geysers, California; Klamath
Falls, Oregon; and the Rio Grande Rift Zone, New Mexico. It is
the culmination of the first step — namely, baseline data assess-
ment — towards the goal of developing an environmental monitoring
methodology with primary emphasis on groundwater degradation for
geothermal areas.
The Imperial Valley displays high regional heat flow and
contains six Known Geothermal Resource Areas (KGRAs), where geo-
thermal water ranges approximately from 150° to 300°C (300° to
570°F) in temperature and from 15,000 to 300,000 mg/1 in total
dissolved solids (TDS). The valley is a sediment-filled struc-
tural trough undergoing intensive crustal deformation, active
faulting, very high seismicity and significant subsidence. An
extensive data compilation has resulted in a new comprehensive
fault map of the valley. Groundwater quality varies from potable
water to geothermal brines. Irrigation water considerably
affects the natural groundwater system in the valley. Modified
Stiff diagrams, Langelier-Ludwig diagrams and computer-generated chemi-
cal parameter surface plots have been useful in depicting the geo-
hydrologic and chemical characteristics of groundwater in the valley.
Geysers geothermal field produces steam of about 230°C
(445°F) from a fractured greywacke formation. Numerous faults and
notable seismic activity occur in this mountainous region. Com-
pared to the surrounding area, an anomalously high level of micro-
earthquake activity is concentrated at The Geysers geothermal
field. Hydrology and water quality are discussed for nine drain-
age basins in The Geysers region. Much of the groundwater has a
naturally high boron content.
Geothermal water is being utilized in Klamath Falls, Oregon,
for space heating. Other geothermal waters occur in the north-
west trending Klamath Basin structural depression. The thermal waters
appear to be associated with faults and are located in rubbly,
fractured basalt aquifers. The dissolved salts in these surface
waters consist mainly of calcium and magnesium bicarboi)ates while
deeper thermal waters contain ^principally sodium and calcium
sulfates, chlorides, and bicarbonates . Four main aquifers, which
include regional, intermediate and local flow systems, are identified
Historically, the area has displayed a very low level of seismicity.
v
-------
The Rio Grande Rift Zone contains seven areas of potential
goethermal interest. Complex folding in the mountins and dis-
continuous faulting throughout the rift zone make the geologic
structure difficult to interpret. Several drainage basins occur
which contain much saline water (> 1,000 mg/1 TDS), and the
available volume of freshwater varies widely. The highest seis-
micity occurs near Socorro, but is of considerably lower level
than in Imperial Valley.
VI
-------
CONTENTS
Foreword
Abstract
Figures
Tables
Plates
INTRODUCTION
1.1 Objectives
1.2 Scope of Investigation
1.3 Baseline Assessment Report
1.4 Report Organization
IMPERIAL VALLEY
2.1 Introduction
2.1.1 Summary
2.1.2 Background
2.1.3 Climatology
2.2 Geothermal Characteristics
2.2.1 Salton Sea Geothermal Area
2.2.2 Heber Geothermal Area
2.2.3 East Mesa Geothermal Area
2.2.4 Brawley Geothermal Area
2.2.5 Dunes Geothermal Area
2.2.6 Glamis Geothermal Area
2.2.7 Cerro Prieto Geothermal Area
Geology
2.3.1 Physiography of the Salton Trough
2.3.2 Tectonic Evolution of the Salton
Trough
2.3.3 Structure of Imperial Valley
2.3.4 Stratigraphy and Lithology of
Salton Trough Rocks
2.3
2.4
Hydrology
2.4.1 Surface Water
2.4.2 Ground Water
2.4.3 Hydrologic Budget
1
3
3
4
7
7
12
12
13
15
16
16
17
18
19
19
20
20
22
31
46
54
54
62
103
vii
-------
page
2.5 Chemical Characteristics of Ground Water 109
2.5.1 Types and Distribution of
Ground Water 122
2.5.2 Single-Chemical Parameter
Contoured Surface Plots 128
2.5.3 Trace Elements in Geothermal Waters 136
2.6 Seismicity 140
2.6.1 Historical Seismicity 140
2.6.2 Microseismicity 142
2.6.3 Seismic Risk 143
2.6.4 Relation of Earthquakes to
Geothermal Activity 147
References 150
3. THE GEYSERS 163
3.1 Introduction 163
3.1.1 Summary 163
3.1.2 Background 164
3.1.3 Climatology 164
3.2 Geothermal Characteristics of The Geysers 169
3.3 Geology 172
3.3.1 Physiography 172
3.3.2 Regional Geologic Setting and
Tectonic History 173
3.3.3 Structure 175
3.3.4 Stratigraphy and Lithology 175
3.4 Hydrology 181
3.4.1 Surface Water 182
3.4.2 Ground Water 182
3.4.3 Hydrologic Budget 190
3.5 Chemical Characteristics of Ground Water 191
3.6 Seismicity 193
3.6.1 Historical Seismicity 193
3.6.2 Microseismicity 196
3.6.3 Seismic Risk 198
References 208
4. KLAMATH FALLS 211
vin
-------
Page
4.1 Introduction 211
4.1.1 Summary 211
4.1.2 Background 211
4.1.3 Climatology 213
4.2 Geothermal Characteristics 221
4.2.1 History of Geothermal Exploration
and Development 221
4.2.2 Temperature Gradients 223
4.2.3 Geothermal Potential 224
4.3 Geology 225
4.3.1 Physiography 225
4.3.2 Regional Geologic Setting and
Tectonic History 227
4.3.3 Structure 230
4.3.4 Stratigraphy and Lithology 233
4.4 Hydrology 240
4.4.1 Surface Water 240
4.4.2 Ground Water 247
4-4-3 Hydrologic Budget 254
4.5 Chemical Characteristics of Ground Water 254
4.5.1 Chemistry of Thermal Waters 258
4.6 Seismicity 261
4.6.1 Historical Seismicity 261
4.6.2 Seismic Risk 261
4.6.3 Seismicity and Tectonism 263
References 266
5. RIO GRANDE RIFT ZONE 269
5.1 Introduction 269
5.1.1 Summary 269
5.1.2 Background 270
5.1.3 Climatology 272
5.2 Geothermal Characteristics 281
5.3 Geology 286
5.4 Hydrology 289
5.5 Chemical Characteristics of Ground Water 301
IX
-------
page
5.6 Seismicity 310
5.6.1 Seismicity Along the Rio Grande
Rift 310
5.6.2 Seismicity of the Valles Caldera
Region 315
References 31^
Appendices
A Geologic Time Scale 320
B U.S. - Metric Conversion Table 321
C Basic Concepts and Semantics of Hydrology 323
D Glossary 329
E List of Abbreviations 337
x
-------
FIGURES
Dumber page
1.1 Location of study areas 2
2.1 Physiographic setting and location of
Imperial Valley, California 8
2.2 Temperature gradient map showing locations of
KGRAs in Imperial Valley, California 9
2.3 Mean annual precipitation, 1931-1960,
Imperial Valley, California 14
i
2.4 A and B. Simplified diagram of "rhomb graben"
formation
C. Multiple "rhomb graben" formation 25
2.5 Tectonic setting of the Gulf of California 26
2.6 Schematic model for the evolutionary
development of the Salton Trough 27
2.7 Structural interpretation of a ground
magnetometer survey by Kelly and Soske (1936) 29
2.8 Map of possible faults and discontinuities in
the Salton Sea area 42
2.9 Depth to basement complex, Imperial Valley,
California 45
2.10 Location of sections, porosity profile
sites and wells referenced in this report 48
2.11 Cross section of average percent volume of
sand bodies in sedimentary section 49
2.12 Composite column of Salton Trough showing
inferred time-stratigraphic relations,
estimated maximum thickness and lithology 50
2.13 Salton Sea drainage basin 55
XI
-------
Number Page
2.14 Total thickness of deposits with water
containing less than 35,000 mg/1 dissolved
solids 67
2.15 Total thickness of deposits with water
containing less than 35,000 mg/1 dissolved
solids in zone 4 68
2.16 Total thickness of deposits with water
containing less than 35,000 mg/1 dissolved
solids in zone 3 69
2.17 Total thickness of deposits with water
containing less than 35,000 mg/1 dissolved
solids in zone 2 70
2.18 Total thickness of deposits with water
containing less than 35,000 mg/1 dissolved
solids in zone 1 71
2.19 Hydrologic section A-A1 72
2.20 Hydrologic section B-B1 73
2.21 Hydrologic section C-C' 74
2.22 Perforated intervals for wells in Imperial
Valley, California 77
2.23 Ground water level contours of shallow
aquifer system, 1962 and 1964, in Imperial
and Mexicali Valleys 79
2.24 Inferred direction of movement in the deep
water-bearing strata to generalized areas
of known geothermal anomalies in Imperial
and Mexicali Valleys 80
2.25 Change in ground water levels in East Mesa,
1939-1960 85
2.26 Average ground water level contours in 1939
in the Colorado River Delta region 86
2.27 Correlation between horizontal and vertical
permeabilities, East Mesa KGRA, Imperial
Valley, California 93
XII
-------
Number page
2.28 Porosity versus depth for two wells in south-
east Imperial Valley 95
2.29 Porosity versus depth for two wells in central
and northern Imperial Valley 96
•2.30 Correlation between core permeability and
core porosity, East Mesa KGRA, Imperial
Valley, California 97
2.31 A. Basic model of a geothermal system 101
B. Modified model for Salton Sea geothermal
system, showing source of recharge and
water quality changes 101
2.32 Complete Bouguer anomaly map of the Imperial
Valley 104
2.33 Static temperature profiles in geothermal
wells from the Salton Trough 105
2.34 Modified Stiff diagrams for characteristic
Imperial Valley ground waters 113
2.35 Three-dimensional perspective of a Langelier-
Ludwig diagram showing surfaces of salinity
sections 115
2.36 Langelier-Ludwig diagram for ground water
data in Imperial Valley, California 116
2.37 ' Salinity section A-B from Langelier-Ludwig
diagram for ground water data in Imperial
Valley, California 117
2.38 Salinity sections A-C and A-D from Langelier-
Ludwig diagram for ground water data in
Imperial Valley, California 118
2.39 Modified Stiff diagrams representing
hypothetical analyses of ground water
resulting from specified chemical changes
in Colorado River water 120
2.40 Schematic surface of specific conductance
values in Imperial Valley ground water 129
2.41 Schematic surface of sulfate values in Imperial
Valley ground water 130
-------
Number
2.42 Schematic surface of bicarbonate values in
Imperial Valley ground water 131
2.43 Schematic surface of chloride values in Imperial
Valley ground water 132
2.44 Schematic surface of calcium values in Imperial
Valley ground water 133
2.45 Recurrence curve for earthquakes in the
Imperial Valley region, 1932-1972 145
2-46 Ranges of maximum acceleration in rock 146
2.47 Comparison of maximum acceleration in rock
and stiff soil deposits for earthquake
magnitude 7 146
2.48 Epicenters of injection-induced earthquakes
at Rangely, Colorado 149
3.1 Location map of The Geysers study area 165
3.2 Precipitation in The Geysers-Clear Lake area 168
3.3 Earthquake epicenters located by the University
of California, Berkeley, 1910-1976 194
3-4 Frequency of occurrence of earthquake
intensities, Santa Rosa Valley region 199
3.5 Magnitude versus frequency of occurrence
for earthquakes in the central Coast Range 201
4.1 Location map of the Klamath Basin study area 212
4.2 Normal monthly temperature and precipitation
at Klamath Falls 215
4.3 Annual precipitation at Chiloquin and Klamath
Falls, 1902-1972 217
4.4 Diagrammatic section of east side of Klamath
graben 235
4.5 Salient features of local, intermediate and
regional ground water flow systems 252
xiv
-------
Number page
4.6 Earthquake epicenters in Oregon, 1841-1970 262
4.7 Magnitude versus frequency of occurrence for
earthquakes in the Basin and Range Physio-
graphic Province of southern Oregon 264
5.1 Map of Rio Grande Valley and area of direct
surface runoff 271
5.2 Rio Grande drainage basin in New Mexico 273
5.3 Major topographic subdivisions of Rio Grande
Rift 274
5.4 "Narrow" interpretation of Rio Grande Rift
Zone 275
5.5 Average annual precipitation and lake surface
evaporation 277
5.6 Normal annual precipitation in New Mexico 278
5.7 Life and crop zones in New Mexico 279
5.8 Vegetative-type map of New Mexico 280
5.9 Heat flow in New Mexico 282
5.10 Subdivisions of the Rio Grande Rift 284
5.11 Average monthly and annual discharges at
selected gaging stations, Rio Grande Valley
and area of direct surface runoff 292
5.12 Mean discharge of principal streams and annual
runoff in New Mexico for periods of record 293
5.13 Decline of ground water level in Estancia Basin,
Santa Fe and Torrance Counties, New Mexico, 302
1848-1960 ,
5.14 Depth to ground water in New Mexico 303
5.15 Ground water reservoir in the Rio Grande
Depression, New Mexico 304
5.16 Average annual suspended sediment discharge
of streams and suspended sediment discharge
by years at selected stations in New Mexico 305
xv
-------
Number
5.17 Average annual dissolved solids discharge in
years at selected stations in New Mexico 306
5.18 General occurrence of saline ground water in
New Mexico 307
5.19 Thickness of fresh water unit (less than
one gram per liter dissolved solids) 308
5.20 General availability of relatively fresh
ground water in New Mexico 309
5.21 Principal sources of waste water in New Mexico 311
5.22 Seismic risk map by Richter (1958) 313
5.23 Seismic risk map by Algermissen (1969) 314
xvi
-------
TABLES
-Dumber page
1.1 ' List of principal project participants 6
2.1 Fault map reference 33
2.2 Chemical analyses of water from the Salton Sea 59
2.3 Selected chemical analyses of surface water in
the Salton Sea Basin 61
2.4 Summary of "usable" and recoverable water in
storage derived from the Colorado River and
local sources 89
2.5 Results of USGS pumping tests in Imperial
Valley, California 91
2.6 Trace element composition of Salton Trough
geothermal waters 137
3.1 Average monthly and annual temperatures and
precipitation at selected stations 167
3.2 Average annual stream discharge and depth
of runoff 183
3.3 Modified Mercalli intensity scale 195
3.4 Earthquake recurrence data for the
central Coast Range region 202
4.1 Mean monthly and annual temperatures and
precipitation, and mean extremes of
temperature, Klamath Basin, 1931-1960 216
4.2 Prevailing winds at Klamath Falls airport:
percentage frequency of occurrence of calms
and modal directions, with average speeds 219
4.3 Summary of stream flow data at selected points
in the Klamath Basin 243
XVll
-------
Number
4.4 Chemical analyses of surface waters, 1959-1963
averages 248
4.5 Aquifer units of Klamath Basin 249
4.6 Chemical analyses of waters from springs and
wells 255
5.1 Mean temperature and precipitation at places
in the Rio Grande Basin, New Mexico 276
5.2 Generalized stratigraphic section in the
Rio Grande Basin, New Mexico 288
5.3 Average Class A land pan evaporation, Rio
Grande Basin in New Mexico 290
5.4 Annual discharge of the Rio Grande near
Lobatos, Colorado 295
5.5 Annual discharge of the Rio Grande at
San Marcial, New Mexico 297
5.6 Annual discharge of the Rio Grande at
Fort Quitman, Texas 299
XVlll
-------
PLATES
Number All plates in pocket
2.1 Geologic map, Imperial Valley, California
2.2 Fault map, Imperial Valley, California
2.3 Well location map, Imperial Valley, California
2.4 Chemical characteristics of shallow depth ground-
water, Imperial Valley, California
2.5 Total dissolved solids in shallow depth ground-
water, Imperial Valley, California
2.6 Chemical characteristics of intermediate depth
groundwater, Imperial Valley, California
2.7 Total dissolved solids in intermediate depth
groundwater, Imperial Valley, California
2.8 Chemical characteristics of deep ground-
water, Imperial Valley, California
2.9 Total dissolved solids in geothermal
water, Imperial Valley, California
2.10 Historic seismicity map, Imperial Valley, California
3.1 Preliminary field compilation of in-progress geologic
mapping in The Geysers geothermal area, California
(2 sheets)
3.2 Map showing preliminary hypocenters of earthquakes
in the Healdsburg Quadrangle, Lake Berryessa to
Clear Lake, California
4.1 Geologic map of the southern Klamath Basin and
adjacent areas
5.1 Rio Grande Rift in New Mexico
xix
-------
SECTION 1
INTRODUCTION
This is the first in a series of reports concerning the
environmental assessment of effluent extraction, energy conver-
sion, and waste disposal in geothermal systems. The primary
objective of the study is to provide the United States Environ-
mental Protection Agency (EPA) with a monitoring approach to
detect any ground water pollution, induced seismicity and/or in-
duced subsidence caused by geothermal resource development.
This approach is expected to serve as a model for monitoring any
geothermal area. An important part of this study involves
environmental assessment of four geothermal areas: Imperial
Valley and The Geysers, California; Klamath Falls, Oregon; and
the Rip Grande Rift Zone, New Mexico (Fig. 1.1). Each of these
areas is representative of a distinct type of geothermal system.
The Imperial Valley is representative of an intermediate to high
temperature liquid-dominated system; The Geysers, of a vapor-
dominated system; Klamath Falls, of a low temperature hot water
system; and Rio Grande Rift, of a hot, dry rock system, and a
high temperature liquid-dominated system.
This assessment requires evaluation of the geologic, hydro-
logic, climatic and seismic conditions, and definition of poten-
tial pollutants and environmental effects. From the data base
provided by this assessment, a monitoring system will be de-
signed, implemented and evaluated at one of the four areas.
1.1 OBJECTIVES
The objective of this study is to acquire and analyze data
for the purpose of:
1) identifying pollutants as a result of geothermal
development,
2) identifying pathways into the underground water
environment,
3) identifying ecological hazards involved with long-term
operating facilities,
-------
*£&V ^LAMA^^ttS' ' > ^'f%
fe4r
-------
4) designing a monitoring approach that will be appli-
cable to any geothermal resource development and
conversion facility, and
5) applying the methodology to a selected site and oper-
ating the system to verify its applicability.
The primary emphasis is on the environmental effects of
changes in the ground water regime, both chemical and hydraulic,
as a result of geothermal resource utilization. The primary
effects are potential ground water pollution, subsidence, and
induced seismic events which in turn may affect the ecology and
socioeconomic conditions of the areas.
1.2 SCOPE OF INVESTIGATION
The scope of work is outlined in five tasks to be accom-
plished in three stages. Stage I is an assessment stage that
includes Tasks 1 and 2. Task 1 will define the geology, hydrol-
ogy, climatology and seismicity of the four geothermal areas
and identify the aquifers in each area. Task 2 will define the
various geothermal systems,- quantify the pollutants from geo-
thermal resources development, including phase of the produced
fluids, subsidence possibilities, seismic effects, fluid dis-
posal methods and thermal losses; and discuss their possible
effects on the ground water of each area.
Stage II is a design and research stage that includes Task
3, resulting in the design of a monitoring system for one of the
four areas.
Stage III includes Tasks 4 and 5 and is a monitoring,
analysis and evaluation stage. Task 4 involves implementation
and operation of the monitoring program under the direction of
the project officer. Recommendations for improvement in the
monitoring plan will be incorporated into Task 5. As a result
of the experience in designing and operating a monitoring sys-
tem, recommendations for a general monitoring methodology that
will be most apt to meet the requirements of any geothermal
resource development will be the culmination of Task 5.
1.3 BASELINE ASSESSMENT REPORT
This report, the result of the Task 1 investigation, sum-
marizes, evaluates and synthesizes all available, relevant data
on climatology, geology, hydrology and seismicity for the four
geothermal areas previously mentioned. No original field work,
laboratory research or chemical analyses were conducted, al-
though some novel and valuable syntheses and representations of
existing data were accomplished.
-------
The goal of this report is to establish baseline and back-
ground data on each of the four areas. This will define what is
known about the existing physical conditions so decisions on
development of a monitoring system can be made.
The level of information necessary for subject evaluation
in geology, hydrology, climatology and seismicity for each type
Of geothermal system will be established. Different levels of
subject information will exist for each geothermal area, and it
will be necessary to define a minimum number and quality of
parameters to establish a viable and meaningful monitoring
program that would be particularly responsive to each specific
type of geothermal environment.
To describe potential effects on a ground water system,
information is necessary describing physical properties and
lithology of subsurface materials, permeability and hydraulic
gradient, geometry of aquifers and aquitards, recharge and
discharge areas and areal distribution of the chemical quality
of the ground water. The physical properties and lithology of
subsurface materials will determine what basic role each unit
will play. For example, with this information deductions can be
made about the underground flow system: will the unit conduct
or resist water flow; is the flow intergranular or along frac-
tures; will anisotropy preferentially induce more flow in one
direction; what chemical changes due to underground flow can be
expected from the solubility of the mineral constituents in
geologic units; etc. Knowledge of the permeability, hydraulic
gradient and geometry of aquifers and aquitards combined with
lithologic information will allow estimates of the rate and
direction of flow. Recharge and discharge areas must be known
to trace the flow patterns and to predict the effects of man-
induced recharge or discharge. Areal distribution of the chemi-
cal quality of ground water, including isotope data, will aid in
identifying the sources of the water and provide some indication
about flow patterns and interconnection of aquifers.
The seismicity portion of the study requires an under-
standing of the tectonic framework of the area being monitored.
A record of historic, predevelopment seismic activity and an
instrumentation network to monitor current activity would be
necessary. For example, knowledge of the tectonic history and
structural framework of the Salton Trough plays an integral part
in understanding the causes of existing seismicity patterns and
will aid in distinguishing between natural seismicity and seis-
micity which may result from geothermal development.
1.4 REPORT ORGANIZATION
This report was prepared by an interdisciplinary team of
scientists from Geonomics, Inc., GeothermEx, and W. K. Summers
-------
and Associates. Section 1 (Introduction) and Section 2
(Imperial Valley) were prepared by economics, Inc. The major
portions of Sections 3 and 4 were prepared by GeothermEx and the
major portion of Section 5 by W. K. Summers and Associates.
Table 1.1 is a list of individuals who participated in the
preparation of this report.
% This report is arranged in five sections and five appen-
?Sices. Each of the baseline studies follows a general outline,
consisting of subsections on geothermal characteristics, geol-
ogy/ hydrology, chemical characteristics of ground water and
seismicity. Each baseline study also includes an introductory
section containing a summary, as well as information on back-
ground and climatology. References are cited at the end of each
section. The format for the studies of each region was kept as
consistent as possible, and most of the subsections are consis-
tent between regions down to third-order headings. Variations
in the micro-organization are due to different amounts of avail-
able data and different geologic, hydrologic and seismic condi-
tions in each region.
Several topics discussed under individual regions are
worthy of particular attention. The "Chemical Characteristics
of Ground Water" section in the Imperial Valley study contains a
number of standard and some novel approaches to establishment of
baseline ground water conditions. The "Relation of Earthquakes
to Geothermal Activity" section in the Imperial Valley study and
the "Seismic Risk" discussion in The Geysers study both contain
much information of general interest that could relate to any
geothermal area.
The five appendices at the end of this report contain addi-
tional background information to aid in understanding some of
the more technical material. The first appendix is a geologic
time scale to accompany the geologic discussions. The second
appendix contains U.S.-to-metric conversion factors used in this
report. The third appendix is a discussion of concepts and
semantics of hydrology. The fourth appendix is a glossary
containing important technical terms used in this report. The
fifth appendix is a list of abbreviations used in this report.
-------
TABLE 1.1 LIST OF PRINCIPAL PROJECT PARTICIPANTS
GEONQMICS, INC.
Project Management:
H. Tsvi Meidav, Project Manager
Subir K. Sanyal, Deputy Project
Manager and Scientific Coordinator
Geology and Hydrology:
Seismology:
Chemistry:
Geochemistry:
Computer Graphics:
Research, Administration:
Editing:
Imperial Valley Area
Richard B. Weiss
Theodora Oldknow
Maren Teilman
Maren Teilman
Richard B. Weiss
Felix Tsai
Franco B. Tonani
Richard B. Weiss
Theodora Oldknow
Sirisak Juprasert
Gio' M. Morse
Evelyn Bless
GEOTHERMEX
W. K. SUMMERS & ASSOCIATES
The Geysers Area
James B. Koenig
Roger Greensfelder
Klamath Falls Area
Murray Gardner
The Rio Grand Rift Area
and
Hydrology Appendix
W. K. Summers
-------
SECTION 2
IMPERIAL VALLEY
2.1 INTRODUCTION
This section presents baseline data on climatology, geol-
ogy/ hydrology and seismology to aid in assessment of environ-
mental impacts of potential geothermal development in Imperial
Valley, California. The major emphasis is on ground water
contamination, with detailed descriptions of aspects of clima-
tology, geothermal characteristics, tectonics, faults, stratig-
raphy, lithology and surface water that are related to and
influence the ground water regime. A section on baseline seis-
micity of Imperial Valley, microseismicity and seismic risk is
also included.
2.1.1 Summary
The Sal ton Trough (Fig. 2.1) is an area of high regional
heat flow and contains numerous geothermal anomalies (Combs,
1971) (Fig. 2.2). It is one of the most seismically active
areas in the United States,and significant subsidence rates have
been measured. Geologic evidence shows that the trough has
experienced intensive crustal deformations, active faulting
(Richter, 1958; Allen, et al.,1965; Brune and Allen, 1967) and
subsidence (Elders, et al.,1972) and that this intensive defor-
mation is continuing.
The Imperial Valley (Figs. 2.1 and 2.2) is a hot, naturally
arid area with less than 76.2 mm (3 in) of mean annual precipi-
tation. It is a relatively flat alluvial valley with the central
portion heavily irrigated. It is a broad structural and topo-
graphic depression that has been filled with over 6,000 m
(20,000 ft) of later Tertiary deltaic and lacustrine sands,
silts and gravels overlain by alluvium and lake sediments. The
underlying pre-Tertiary granitic and metamorphic complex is
intensely step-faulted down from the mountains surrounding both
sides of the valley.
The combination of graphic chemical-analytic representa-
tions presented in this report provides an effective basis for
establishing baseline water quality parameters in Imperial
Valley and other geothermal areas. These representations
include modified Stiff diagrams, salinity circles, Langelier-
Ludwig diagrams and single-chemical parameter plots.
-------
00
San Bernardino Mtns.
Desert Hot Springs
India Hills
Little San Bernardino Mtns
Mecca Hills
Santa Rosa Mtns.
Orocopia Mtns.
Tierra Blanco Mtns.
Split Mountain Gorge
Carrizo Wash
Superstition Hills
Figure 2.1 Physiographic setting and location of Imperial Valley, California.
(Coplen, 1976)
-------
TEMPERATURE GRADIENT MAP
OF THE IMPERIAL VALLEY CALIFORNIA
IO(Mil«J
10 15 (Km)
TEMPERATURE GRADIENTS
, , GREATER THAN 10° F
1 | PER 100 FEET IN DEPTH
8" TO 10'f PER IOO FEET
IN DEPTH
LEGEND
AREAS WITH HIGH
TEMPERATURE GRADIENTS
FAULTS WITH REPORTED SURFACE
RUPTURE DURING HISTORIC TIME,
SINCE 1769
6" TO 8° F PER IOO FEET
IN DEPTH
FAULTS WHICH APPEAR TO DISPLACE
QUATERNARY ROCKS OR DEPOSITS
4° TO 8" F. PER
IN DEPTH
2" TO 4" F PER IOO FEET
IN DEPTH
« WILDCAT OIL WELLS ABANDONEn
(SFF t 1ST FDR WFl L No fi N' '
I 1 LESS THAN 2° F PERIOD
1 FEET IN DEPTH
TEMPERATURE GRADIENT DAT A
COMPILED a INTERPRETED BY
JIM COMBS, U.C. RIVERSIDE
SEPT. 1971
Figure 2.2 Temperature gradient map showing locations of KGRAs in Imperial Valley
California. (Palmer, et al,, 1975)
-------
Modified Stiff diagrams, prepared for this report, depict
the areal distribution of the chemical characteristics of waters
in each of three depth zones (Plates 2.4, 2.6 and 2.8). The
three depth zones, based on perforated well intervals, defined
for this study (Fig. 2.22) are shallow, from 24 to 91 m (80 to
300 ft); intermediate, from 91 to 457 m (300 to 1,500 ft); and
deep, more than 457 m (1,500 ft).
The modified Stiff diagrams aided in defining the areal and
depth distribution of five water types in Imperial Valley.
These are a sodium chloride water, a high sulfate water, a
sodium chloride with high sulfate and/or magnesium water, a
sodium chloride with high calcium water and a sodium bicarbonate
water (Fig. 2.34). The Stiff diagrams depict the great varia-
tion in the chemical characteristics of ground water throughout
the valley, from the purest waters coming off the Peninsular
Range to the hypersaline brines occurring in the Salton Sea
geothermal area. The salinity circles (Plates 2.5, 2.7 and 2.9)
and the schematic surface of specific conductance values (Fig.
2.40) define variations of ground water salinity and depict a
salinity gradient, with salinity increasing from the south-
eastern valley to the west and north as well as with depth.
Langelier-Ludwig diagrams (Figs. 2.36, 2.37 and 2.38) show
chemical changes and groupings of waters. Single - chemical
parameter contoured surfaces provide a graphic method for corre-
lating chemical changes in ground water with geologic or struc-
tural features and for recognizing chemical correlations.
The geology of the Imperial Valley (Plate 2.1) is compli-
cated with myriad fault traces (Plate 2.2) and thousands of
meters of discontinuous, folded and layered sediments. The San
Andreas, San Jacinto, Elsinore and Salton Trough Fault Zones are
all components of the San Andreas Fault System that fractures
the sediments and basement of the valley. A detailed compila-
tion of these faults has been prepared for this report (Plate
2.2) and many fault traces have been located in each of these
fault zones. Many other concealed traces in alluvial areas
remain to be discovered with further detailed investigation. The
Salton Trough Fault Zone has been defined in this report as a
unique zone, containing parallel and subparallel fault traces
between the San Andreas and San Jacinto Fault Zones. Most of
the faults in this zone are concealed and have been inferred
from geophysical evidence.
Rocks in the Salton Trough range in age from Precambrian
basement complex to Recent alluvium and dune sands and cor-
respondingly, from dense, competent hard rocks to totally uncon-
solidated sedimentary deposits to young volcanics (Plate 2 1,
Fig. 2.12). Most of the central valley is Pliocene and younger!
One deep well near Brawley intercepted over 4,000 m (13,000 ft)
of interbedded fine-grained sandstone and siltstone. The main
10
-------
source of the thick section of Eocene to Holocene nonmarine
sediments has been, Colorado Plateau debris transported by the
Colorado River, with some contribution from local sources.
Tertiary volcanic and intrusive rocks occur within the sedi-
mentary section.
Imperial Valley ground water generally flows northward and
m»estward as underflow from the Colorado River, canal leakage and
^irrigation discharge (Fig. 2.23). This flow is generally dis-
tributed into a shallow and a deep aquifer. Flow pattern com-
plications arise from fault and stratigraphic aguitards which
channel and restrict water flow. It is conjectured that local
convective patterns tend to cause regional waters to flow radi-
ally inward towards the geothermal anomalies (Fig. 2.24). All
water is discharged from the closed Salton Sea Drainage Basin
through evaporation and evapotranspiration.
The flow rate of wells is quite variable throughout the
valley (Table 2.5), from over 3,800 1pm (1,000 gpm) in a shallow
well in the southeastern valley to essentially nil in some
shallow wells in the central portion of the valley. However,
deep wells in the central portion of the valley flow as well or
better than wells at the valley margins.
The total volume of water in storage has been estimated be-
tween 0.20 and 0.59 billion ha-m (1.6 and 4.8 billion acre-ft),
with another estimate of 0.14 billion ha-m (1.2 billion acre-ft)
of usable and recoverable water in storage.
Artificially induced recharge of Imperial Valley ground
water from irrigation has had a notable effect on ground water
levels, especially in the southeastern portion of the valley.
Seismic activity is widespread and abundant - in Imperial
Valley (Plate 2.10). Nine earthquakes of magnitude 6.7 or
greater have occurred in the Salton Trough since 1850. The
Imperial Valley earthquake of 1940 was the most significant
event in terms of human disturbance. Although it has been
difficult to correlate much of the historic seismicity with
active faults, correlation of microseismicity with active faults
has been more fruitful.
Microearthquake activity is associated with geothermal
anomalies, and their occurrence may increase with geothermal
development or reinjection of geothermal fluids. A number of
microseismic monitoring networks have been installed in Imperial
Valley by the U.S. Geological Survey (USGS), California Insti-
tute of Technology (Cal Tech) and Chevron Oil Company. Changes
in earthquake recurrence statistics and/or in the depth and
location of events from preproduction activity can be used to
determine production-induced seismicity.
11
-------
2.1.2 Background
The Imperial Valley is located in Imperial County in the
southeasternmost corner of California (Fig. l.i). It contains
six Known Geothermal Resource Areas (KGRAs). They are the
Salton Sea, Brawley, Glamis, East Mesa, Dunes, and Heber KGRAs.
The Cerro Prieto field in northern Mexico, also part of the
Salton Trough, is already in production. Ongoing commercial
geothermal activity will involve production from and probable
reinjection into specific reservoir formations.
The Imperial Valley could be divided environmentally into
two segments: 1) the central portion of the valley west of the
East Highline Canal which is heavily irrigated, and 2) the area
east of the canal which is largely barren. Based upon the
difference in land use, we would rank the potential environ-
mental impacts in the agricultural portion of the valley differ-
ently from those in the sandy regions which are uninhabited.
The Imperial Valley is one of the richest farming areas of
the United States with a total agricultural productive capacity
of about $500 million per year. The valley, a flat alluvial
plain, is laced with more than 6,400 km (4,000 mi) of precisely
aligned canals and drains. Any land subsidence due to massive
withdrawal of fluid would create havoc with the hydraulic gra-
dients of these canals and drains. Potentially negative envi-
ronmental impacts in the agricultural area addressed in this
section include induced earthquake activity, induced rise in
ground water levels and ground water degradation.
Previous studies on ground water in Imperial Valley were
conducted by Butcher, et al.,(1972) and Loeltz, et al.,(1975).
Water quality data has been published by Hardt and French
(1976), Reed (1975), Cosner and Apps (1977), Loeltz, et al.,
(1975) and Geonomics (1976). Many investigators have conducted
geologic and seismologic studies in Imperial Valley/ and the
major ones are mentioned in the respective subject sections.
The geothermal anomalies in Imperial Valley were initially
discovered through research programs conducted by the Institute
of Geophysics and Planetary Physics at the University of Cali-
fornia, Riverside (U.C.R.). These researchers have published
many studies on the geothermal occurrences in Imperial Valley,
particularly Rex, et al. (1971) and Rex, et al.,(1972).
2.1.3 Climatology
The Imperial Valley is a naturally arid area. It is a
relatively flat alluvial valley. The central portion west of
the East Highline Canal is heavily irrigated and the area east
of the canal is largely barren. The irrigated portion of the
valley is a rich farmland.
12
-------
In the summer months temperatures as high as 52°C (125°F)
have been recorded and the average daily maximum in July is
about 42°C (108°F) (based on recordings made at Indio, Califor-
nia, from 1877 to 1960) . While subfreezing temperatures have been
recorded, the lowest average daily minimum, occurring in Jan-
uary, is 3°C (38°F). The mean annual temperature for 1931-1960
was 23°C (73°F).
The mean annual precipitation (Fig. 2.3) ranges from less
than 80 mm (3 in ) near the Salton Sea to over 1,020 mm (40 in )
on Mount San Gorgonio, the highest peak in the San Bernardino
Mountains (Fig. 2.1). The mean precipitation over most of the
area, including the irrigable tracts, is less than 200 mm (8
in ). A large part of the runoff generated by precipitation is
absorbed in the alluvium of the valleys and plains. There is an
annual cyclic precipitation pattern. Most rainfall occurs
between October and April, with the major part occurring from
November through March (Hely and Peck, 1964). Precipitation is
virtually nil from May to September, although there have been
occasional years with a significant percentage of the annual
rainfall during this period.
Natural water loss occurs by evaporation from water and
land surfaces and transpiration from vegetated areas. The
combination of these two components of wat-er loss is called
evapotranspiration. Evapotranspiration in humid regions is
generally computed by subtracting mean annual runoff from mean
annual precipitation. This method is valid for the mountainous
regions to the west of Imperial Valley. However, when runoff is
absorbed by alluvial deposits, like those in Imperial Valley,
the method must be modified to include transpiration of absorbed
runoff. Evapotranspiration in the Peninsular Range to the west
of Imperial Valley ranges from about 100 mm (4 in ) at the
valley margin to over 410 mm (16 in ). In the Chocolate Moun-
tains to the east it is about 100 mm (4 in ) and in the nonirri-
gated areas of the valley it is 80 mm (3 in ) or less.
Rates of evapotranspiration in the irrigated parts of the
valley vary considerably with vegetative type and irrigation
practices. They greatly exceed precipitation and are over 910
mm (36 in ) annually over all of the irrigated region; in some
areas the rate may exceed 1,520 mm (60 in ) (Hely and Peck,
1964). This high rate of evapotranspiration results in high
humidity in the irrigated areas.
2.2 GEOTHERMAL CHARACTERISTICS
The Imperial Valley region is potentially one of the most
important geothermal areas in the United States. High heat
flow from the hot, shallow mantle beneath the northern extension
of the East Pacific Rise (Fig. 2.5), together with the faulting
13
-------
0
l 1—r
50 (kilometers)
i
30 (miles)
EXPLANATION
ISOHYET
Shows equal mean annual
precipitation in inches;
interval variable
DRAINAGE-BASIN BOUNDARY
Figure 2.3 Mean annual precipitation, 1931-1960, Imperial Valley, California
(Hely and Peck, 1964)
-------
and fracturing due to rifting, have combined to generate silicic
volcanism and high geothermal gradients in the region.
Within these six Imperial Valley KGRAs (Fig. 2,2) there are
four known geothermal reservoirs, each containing hot brines of
different character: a high-temperature (300°C [572°F]), high-
enthalpy (.1,046 kilojoules/kg [450 BTU/lb], high-salinity
^250,000 ppm total dissolved solids [TDS]) brine, at Niland in
^Jie Salton Sea KGRA; and three other reservoirs with fluids of
lower temperature (up to 200°C [392°F]), enthalpy (around 800
kilojoules/kg [350 BTU/lb] for East Mesa), and salinity (15,000
to 25,000 ppm TDS) at Brawley, Heber and East Mesa. Each of
these reservoirs is in fractured sandstones of youthful geologic
age. Within the Salton Trough, Cerro Prieto, Mexico, 32 km (20
mi) south of the border, is a part of this same geothermal
province which is characterized by fluids with high temperature
and enthalpy, and lower salinity of 15,000 to 20,000 ppm.
The East Mesa field is under development by the U. S.
Bureau of Reclamation (USER); the Heber field is under develop-
ment by a number of private companies, including Chevron, Magma
Power and Republic Geothermal; and the Brawley field is under
development by the Union Oil Company. The Salton Sea field,
which is no doubt one of the largest geothermal fields in the
world, has defied development so far because of the very high
salinity and corrosive characteristics of the geothermal fluids
produced in that area. A joint effort of the Electric Power
Research Institute (EPRI) and San Diego Gas & Electric Company
(SDG&E) to develop a geothermal test facility at Niland is under
way. A number of companies are presently engaged in active
exploration activities in the valley/ and considerable drilling
activity is expected to take place in that area in the near
future.
More detailed descriptions of each of the individual geo-
thermal areas, are outlined below.
2.2.1 Salton Sea Geothermal Area
The Salton Sea KGRA, also known as the Buttes or Niland
geothermal area, is located along the southern shore of the
Salton Sea (Fig. 2.2).
Five Quaternary rhyolite domes are located within the
Salton Sea KGRA (Robinson and Elders, 1971). Elders, et al.,
(1972) have proposed that this geothermal area is the northern-
most landward extension of the East Pacific Rise. Unaltered
deltaic sediments reach a depth of at least 1,500 m (5,000 ft).
No steam is present as a discrete phase in the geothermal reser-
voir, and thermal brines are highly corrosive.
15
-------
Thermal springs first attracted commercial interest in 1927
when three exploratory wells were drilled for steam. In the
1930s, more than 50 shallow wells were drilled for carbon
dioxide production. It was not until 1957, when the first deep
hole was drilled, that large amounts of thermal brines were
encountered. Twelve additional wells have been completed in the
last decade. Testing to estimate power generation potential is
concentrated in several wells near Obsidian Butte. Although the
Salton Sea KGRA probably contains the greatest volume and high-
est temperature fluids in the Salton Trough, development of this
resource has been hampered by the high salinity and corrosive-
ness of the fluid.
SDG&E and the U.S. Enerqy Research and Development Administration
(ERDA) have installed a 10 MW geothermal test facility. Law-
rence Livermore Laboratory (LLL) is experimenting with scale
corrosion and efficient conversion of geothermal energy for
electric power. Both of these programs are trying to resolve
the technological problems involved in utilizing the high tem-
perature, high-salinity geothermal fluid characteristic of the
Salton Sea KGRA.
2.2.2 Heber Geothermal Area
The Heber geothermal area is south of El Centre (Fig. 2.2),
within an extensive array of cultivated fields. It is a flat
region, near sea level, and has no rock outcrops.
The geothermal anomaly was discovered by a wildcat well
drilled by Amerada Hess Corporation in 1945. The Chevron Oil
Company confirmed this discovery with a shallow test hole in
1963. Since then, various companies have drilled wells. The
Chevron Oil Company and Magma Thermal Power Company wells have
both produced thermal waters (Palmer, et al.,1975). Heber is
one of several water-dominated geothermal fields in the Salton
Basin physiographic province.
The Heber geothermal anomaly is in the moderate temperature
range. Salinity is much lower in Heber than in the Salton Sea
(Palmer, et al.,1975). The lithology of the geothermal reser-
voir includes sands, silts and shales. An 18 m (60 ft) thick
layer of gabbro at 1,340 m (4,400 ft) depth has been reported
from one well in the area (Butler, pers. comm., 1976).
2.2.3 East Mesa Geothermal Area
The East Mesa KGRA is located east of the town of Holtville
(Fig. 2.2). It is on the eastern flank of the Salton Trough.
Wildcat wells in the area indicate deltaic sediments reach a
depth greater than 3,200 m (10,600 ft). Bedrock is about 3,700
m (12,000 ft) deep (Bureau of Reclamation, 1974). These deltaic
sediments are predominantly quartz and calcite, with some
16
m
-------
dolomite, plagioclase, potassium feldspars, mica and clay; gyp-
sum occurs sporadically throughout the sediments (Muffler and
Doe, 1968).
USER in cooperation with the USGS, the National Science
Foundation (NSF) and others is evaluating the East Mesa KGRA to
determine the full extent of the field and its capability for
production of desalted water from geothermal fluids. USER located
Jive deep well sites on the basis of geophysical surveys. Wells
Save been drilled at these sites and are being tested for produc-
tivity and to estimate reservoir conditions. Geothermal produc-
tion well Mesa 6-1 was drilled to a total depth of 2,450 m (8,030
ft) . This well has been used to supply geothermal liquid for
desalting equipment shakedown operations and tests, and for other
purposes. Mesa 6-1 has produced primarily from the upper zone,
to a lesser extent from the next two lower zones and probably not
at all from the bottom zones. Test well Mesa 6-2 was drilled to
a total depth of 1,830 m (6,005 ft). Temperature at the bottom
of the hole was measured at 187°C (369°F) and maximum flow was
890 kg/min (1,962 Ib/min). A series of additional flow tests has
been conducted since then. Test well Mesa 5-1 was drilled to a
total depth of 1,834 m (6,016 ft). Bottom hole temperature was
149°C (300°F), and the final flow pressure was 87.5 kg/sq cm
(1,245 psi). Mesa 5-1 is an injection well. Mesa 31-1 was
drilled to a total depth of 1,899 m (6,231 ft). Bottom hole tem-
perature was 157°C (315°F), and final flow pressure was 167 kg/sq
cm (2,376 psi). Two desalting test units have been installed at
the East Mesa test site. Operations have produced high quality
water (Bureau of Reclamation, 1974).
2.2.4 Brawley Geothermal Area
The Brawley KGRA, also known as the North Brawley geothermal
area is located southeast of the Salton Sea, near the town of
Brawley (Fig. 2.2). Meidav and Furgerson (1972) identified the
North Brawley thermal anomaly by the very low resistivity of 0.35
to 0.76 ohm-m at depths greater than 180 m (600 ft). This is a
four-fold decrease in resistivity compared to surrounding rocks.
It would require an eight-fold increase in temperature gradient
were salinity and stratigraphic factors to be ignored. There is
evidence of at least one and perhaps two hydrologic discontinu-
ities from the Sand Hills to a few kilometers northwest of the
town of Brawley which would signify faults and would account for
salinity and/or stratigraphic changes along the line. These dis-
continuities are the Brawley and the Calipatria Faults. These
faults (Plate 2.2) first appeared in the literature on maps by
Rex (1970). Later, gravity surveys confirmed the presence of
large vertical displacements beneath the valley alluvium.
17
-------
The sedimentary section from 0 to 305 m (0 to 1,000 ft) in
the Brawley area contains a lower percent volume of sand bodies
than some other fields in Imperial Valley. In Brawley, well
Amerada Veysey 1 penetrates sediments containing 61% sand. The
deposits of usable and recoverable water in storage have been
estimated to be about 4,000 m (13,000 ft) thick in Brawley
(Dutcher, et al.,1972). A study by U.C.R. has estimated the
.depth to basement in this area to be about 6,100 m (20,000 ft).
2.2.5 Dunes Geothermal Area
The Dunes KGRA is located in southeastern Imperial Valley,
east of Holtville and adjacent to the Sand Hills (Fig. 2.2).
Numerous shallow wells have been drilled in the area and many
have geophysical logs. Randall (1971) described upper portions
of the Cenozoic section in terms of percent volume of sand
bodies per 150 m (490 ft) and observed that major parts of the
section contain as much as 90% unconsolidated, highly porous
sand bodies, with minor amounts of shale. Elders and Bird
(1974) noted the importance of these shale layers in confining
the hydrothermal system, thereby preventing surface expression.
After closely examining cuttings and recoverable core from CEWR
Dunes No. 1 and U.C.R. No. 15, they observed that impermeable shale
layers served as sites for silica deposition by the upward-
circulating hydrothermal waters. This continuing deposition
eventually formed a mushroom-shaped cap rock that sealed the
hydrothermal system.
Coplen (1972) suggests that local waters are almost totally
derived from the Colorado River. These waters are notably low
in salts and therefore are vastly different from the waters in
northern parts of the valley (Rex, 1972).
Much of what is known about regional structure of the Dunes
area has been deduced from geophysical studies. Kovach, et al.
(1962) and Biehler, et al. (1964), on the basis of seismic
refraction data, observed that basement depth increases from 700
m (2,300 ft) to 3,500 m (11,500 ft) as the Sand Hills are
crossed from east to west. Numerous workers have postulated
that a southeastern extension of the San Andreas Fault System
traverses the axis of the Sand Hills (Biehler, et al., 1964;
Garfunkel, 1972a). Combs (1972) and Elders and Bird (1974) have
speculated that this fault and related faults might be respon-
sible in part for the formation of the Dunes hydrothermal
system.
Combs (1971) discovered the Dunes anomaly on the basis of
shallow thermal-gradient boreholes. Combs (1972) suqaested the
"X*!? xt f? oval-shaped feature, 2.6 sq km (1 sq mi) in area,
with the hottest regions near the center, and further suggested
the importance of the self-sealing mechanism. m the hottest
o£rTeS?PU'£;R' ?S'-7^andCC^- Dunes No* x (estimated heat flow, 25
HFU [Combs, 1972]), a silica-cemented sandstone was encountered
18
-------
between 60 and 115 m (197 and 377 ft) depths. Biehler
(1971) completed a detailed gravity survey over the Dunes anom-
aly and obtained a 2 milligal (mgal) positive closure that
corresponds in shape with the thermal anomaly, although the
gravity closure is centered almost 1.9 km (1.2 mi) to the north-
east of the thermal anomaly. Biehler (1971) attributed this
closure to the existence of the higher density silicified sand
tody as encountered at U.C.R.Nb. 115. Black, et al. , (1973)
easured two orthogonal, 3 km (1.9 mi) long, resistivity
profiles over the center of the Dunes anomaly, indicating that
resistivity drops by 50% over the geothermal anomaly, at least
to a depth of 200 m (660 ft). Van De Verg (pers. comm., 1975)
did seismic refraction profiling over the Dunes anomaly and
noted that basement depths do not change greatly at or near the
anomaly. In summary, the Dunes anomaly can be characterized as
a 2.6 sg km (1 sq mi) region of high heat flow, local positive
gravity and depressed electrical resistivity. However, reversal
of the temperature gradient at about 100°C (212°F) and 305 m
(1,000 ft) depth (Coplen, et al.,1973) reduces hopes of devel-
oping this area at this time.
2.2.6 Glamis Geothermal Area
The Glamis KGRA is about 32 km (20 mi) east of the town of
Brawley, astride the Sand Hills and the trace of the San Andreas
Fault (Fig. 2.2). Interest in this area was precipitated by a
temperature gradient reported to be greater than 2.2°C/100 m
(36°F/300 ft) (Rex, 1970). However, this gradient was based on
one shallow drill, and further exploration in this area has been
disappointing. The initial drill hole probably intersected an
isolated hot spring. Basement is shallow here ,and a gravity
anomaly, which is often typical of geothermal reservoirs, is not
present.
2.2.7 Cerro Prieto Geothermal Area
The Cerro Prieto geothermal area is 35 km (22 mi) south-
southeast of Mexicali, Baja California. This geothermal field is
located along the projection of the Elsinore and San Jacinto
Faults into the Salton Trough. A number of subparallel faults
strike northwest in this area (Reed, 1972).
The local area is topographically dominated by a rhyo-
dacitic, Holocene volcano, Cerro Prieto, located 4 km (2.5 mi)
west of the geothermal field. Hydrothermal activity extends for
approximately 40 sq km (15 sq mi) and is expressed by northwest
trending, linear zones of mud volcanos and hot springs (Mercado,
1968).
Reed (1972) describes the sediments penetrated by wells at
Cerro Prieto as representative of a marginal area of the late
Cenozoic Colorado River Delta, of which the bulk of sediment is
19
-------
sandstone and shale similar in mineralogy to the central Colo-
rado Delta deposits of Imperial Valley described by Muffler and
Doe (1968). Interfingering with these sediments are fanglomer-
ates and alluvial sands derived from the local mountains.
At Cerro Prieto, a 75 MW geothermal power plant has been in
operation since 1973. A second 75 MW plant is currently under
construction. Of the many geothermal areas in western North
America, the Cerro Prieto geothermal area is the only producing
field with a two-phase (steam and water) flow. Other fields of
this two-phase type now in the exploration stage will be able to
benefit from information gained by development at Cerro Prieto.
2 . 3 GEOLOGY
The geology of the Imperial Valley area is quite complex
and is described in the following four sections. The first
section describes the physiography of the Salton Trough in
general, with emphasis on Imperial Valley. The second section,
"Tectonic Evolution of the Salton Trough," explains background
information on past and present tectonic mechanisms in the
Salton Trough. It presents a context in which to view the areal
occurrence of geothermal anomalies and the areal and temporal
patterns of faulting, sedimentation and seismicity of Imperial
Valley. The third section provides the structural geology of
Imperial Valley and extensively refers to a complete fault map
(Plate 2.2) specially prepared for this report. The last sec-
tion describes the stratigraphy and lithology of Salton Trough
rocks. This description is augmented by Plate 2.1, which shows
the geology of Imperial Valley, and by Fig. 2.12, a composite
column of the Salton Trough showing inferred time-stratigraphic
relations, estimated maximum thickness and lithology.
2.3.1 Physiography of the Salton Trough
The Imperial Valley geothermal areas are located in the
Salton Trough geologic province of the western United States and
Mexico (Figs. 2.1 and 2.2). The Salton Trough is the northern
landward extension of the Gulf of California (Dibblee, 1954),
separated from the gulf by the Colorado River Delta. It extends
southward to the gulf and is protected from inundation by the
crest of the Colorado River Delta. The delta crest, in Mexicali
Valley, south of the international border, rises to over 30 m
(100 ft) west of the Yuma Valley (Fig. 2.1).
v /-,™6 S^on Trough is roughly a triangular area, about 210
km (130 mi) long north to south and widening to 110 km (70 mi)
in the southern portion. Mesozoic mountains, consisting of
older metasedimentary and granite basement rocks with some
Tertiary volcanics, border three sides of the steeply step-
faulted basement complex of the Salton ( Trough. This complex
20
-------
structural and topographic depression is bounded on the north by
San Gorgonio Pass, which is between the San Jacinto and San
Bernardino Mountains. It is bounded on the east by the Little
San Bernardino and Chocolate Mountains and on the west by the
San Jacinto, Santa Rosa and Coyote Mountains of the Peninsular
Range.
5. Topographically, the Salton Trough is a broad, flat area
Covered by alluvium. It is commonly divided into four distinct
physiographic units from north to south (Fig. 2.1). They are
the Coachella Valley, the Salton Sink, the Imperial Valley and
the Mexicali Valley. The trend of the entire trough as well as
each of its parts is northwest-southeast. The Coachella Valley
is about 71 km (44 mi) long and 13 to 23 km (8 to 14 mi) wide.
The Salton Sink is the lowest part of the valley and is cur-
rently inundated by the Salton Sea. The Salton Sea also trends
northwest-southeast and is about 42 by 14 to 23 km (26 by 9 to
14 mi).
Flooding of the Colorado River in 1904-1907 created the
present-day Salton Sea. The sea had a surface elevation of 71 m
(232 ft) below sea level in 1968; however, the lowest land
elevation beneath the sea is about 84 m (275 ft) below sea level
(Littlefield, 1966). Constant high evaporation losses, as well
as solutions of salt in sediments underlying the sea (California
Department of Water Resources, 1970), are major factors in
producing the very high salinity of Salton Sea waters.
Imperial Valley is immediately south of the Salton Sea. It
trends north-northwest, about 56 km (35 mi) in length,
about 64 km (40 mi) wide at the north, spreading to about 113 km
(70 mi) at the international boundary.
The major part of Imperial Valley is below sea level.
Streams flow from the Chocolate Mountains on the east and the
Peninsular Range on the west toward the center of the valley.
Natural surface drainage in the central portion of the valley is
carried mainly by the New and Alamo Rivers, which have incised
channels to 12 m (40 ft). Most of the myriad irrigation canals
in the valley eventually discharge into these two rivers.
The Imperial Valley consists of four subareas. They are,
from east to west, the Sand Hills area, the East Mesa area, the
main valley area and the West Mesa area (Fig. 2.18). Most of
the Sand Hills area consists of transverse dune ridges, with up
to 90 m (300 ft) of relief, and smaller barchan or barchan-like
sand dunes. The East Mesa is a triangular area southwest of the
Sand Hills and is a sloping surface that merges gradually with
the main valley area. The main valley area is bounded essen-
tially by the shorelines of prehistoric Lake Cahuilla and
contains the soft, silty lacustrine deposits of this lake. It
is a large area of cultivated and irrigated land. The soils
21
-------
here contain a larger proportion of clay and silt than the
sandier soils of the adjacent East and West Mesa areas. The
land surface is extremely flat, with an average gradient of 0.32
m/km (1.7 ft/mi) from the international boundary to the lowest
part of the valley in the Salton Sea. The volcanic features of
Obsidian Butte and other rhyolite obsidian buttes outcrop near
the southern shore of the Salton Sea.
The West Mesa area is topographically complex and lies
between the main valley area and the Peninsular Range to the
west. Altitudes range from more than 30 m (100 ft) below sea
level in the northwestern part of the area to over 600 m (2,000
ft) at the foot of the Peninsular Range in the southwestern
part. Spurs and inliers of the Peninsular Range consisting
mainly of basement-complex rocks appear on the West Mesa as the
Fish Creek, Coyote and Jacumba Mountains and the Superstition
Mountain. Western Imperial Valley is drained by San Felipe
Creek.
The Mexicali Valley is the part of the Colorado River Delta
which is above sea level and is largely south of the interna-
tional boundary. It is 113 km (70 mi) wide at the international
boundary and continues for 97 km (60 mi) southward to the Gulf
of California. This report will focus on the Imperial Valley
section of the Salton Trough.
2.3.2 Tectonic Evolution of the Salton Trough
Hypotheses concerning the tectonic evolution of the Salton
Trough are still being developed and improved. A simplified
outline of the most currently accepted hypothesis, proposed by
Elders, et al. (1972), is presented below. This hypothesis is
based on a crustal spreading model,and while broad features and
processes are explained, some details still remain enigmatic.
The authors note that any theory must reconcile the following
observations:
1) right lateral strike-slip motion in the trough,
2) sinking of the center of the trough relative to the
sides,
3) areas with enormously high temperature gradients,
4) volcanism suggestive of localized melting,
5) geophysical evidence of rapid lateral changes in the
crust from north to south,
6) crustal thinning from 32 km (20 mi) in the north to 22
km (14 mi) in the south, and
22
-------
7) widespread seismicity.
The development of the Salton Trough according to the
crustal spreading model will be traced from the Mesozoic era to
the present. Two main events relevant to the evolution of the
trough were occurring during the Mesozoic. The first was the
formation of the core of the Peninsular Range by intrusion of a
^Cretaceous batholith into Mesozoic metasediments and metavol-
:f:anics (Jahns, 1954; Allison, 1964) and minor Paleozoic rocks
'(McEldowney, 1968). In the second relevant Mesozoic event,
Paleozoic and Precambrian cratonic rocks of the Basin and Range
Province were undergoing Mesozoic orogeny, deformation and
metamorphism and were being invaded by Mesozoic to early Ter-
tiary granitic plutons (Burchfiel and Davis, 1972; Silver, 1971;
Suppe and Armstrong, 1971).
Since the source of the clasts in the Cretaceous and Eocene
sediments on the eastern slope of the Peninsular Range was to
the east of the present-day Gulf of California (Minch, 1972),
the Peninsular Range must have been opposite the state of
Sonora, Mexico, at least during Cretaceous to Eocene time.
Movement on the ancestral San Andreas Fault brought the Penin-
sular Range northward.
Correlation of basement terrains in the Orocopia Mountains,
San Gabriel Mountains and the Fort Tejon Pass region indicates
about 300 km (190 mi) of fault displacement since the Oligocene
epoch on the active trace of the San Andreas Fault (Crowell,
1962). Inactive faults east of Orocopia show additional slip
which would bring the total displacement to about 600 km (375
mi) since the late Cretaceous or early Tertiary (Garfunkel,
1972 a). This displacement is consistent with the Peninsular
Range sediment source,being to the east of the present Gulf of
California.
During the early or mid-Tertiary, as the Peninsular Range
was progressing northward, movement was accelerating on the San
Andreas Fault while motion between the Pacific Plate and North
American Plate was gradually decreasing. By post-Miocene time
all the motion was transferred to the numerous en-echelon right-
lateral faults of the San Andreas System,and it became the plate
boundary. The continental sliver including Baja,California, and
part of southern California to the west of the San Andreas then
became part of the Pacific Plate (Garfunkel, 1972a). Although
this general conceptual model is understood, the details of this
plate boundary migration still remain unclear (Elders, et al.,
1972).
The gaps produced by tensional forces offsetting the en-
echelon, right-stepped, right-lateral, strike-slip faults of the
San Andreas System formed the depressions of the Gulf of Cali-
fornia and the Salton Trough. These gaps are called "rhomb
23
-------
grabens" by Garfunkel (1972a). Figures 2.4A and 2.4B are sim-
plified diagrams of "rhomb graben" formation; Fig. 2.4C depicts
multiple "rhomb graben" formation.
The northern part of the gulf was formed by this mechanism
by late Miocene time, and Baja California was transferred from
the Mexican mainland within the last 4 million years (Larson, et
al.,1968).
The crustal thinning from north to south noted by Elders,
et al. (1972), and the formation of the Salton Trough structural
low and consequent sedimentary deposition, support the "rhomb
graben" formation theory.
A map of the Gulf of California and Salton Trough showing
the actual "rhomb grabens" based on geophysical evidence is
shown in Fig. 2.5. Elders, et al. (1972) also suggest that
magma generated at depth tends to rise towards the surface where
these deepening and widening rifts are formed as successive
sections of the crust are slid off along strike-slip faults.
Figure 2.6 is a schematic model, oriented parallel to
the strike-slip faults, depicting four stages of evolutionary
development of the Salton Trough. The beginning stage (Fig.
2.6A) shows two crustal layers, a lighter one over a denser one,
experiencing heating from a hot zone in the mantle. In the
second stage (Fig. 2.6B) the lower crust undergoes ductile
thinning while the upper crust is brittle and fractures under
the tensional forces caused by both the upwelling mantle and the
strike-slip motion of the faults. This process causes down-
faulting of the less dense crust and consequent accumulation of
low density sediments in the trough. The sedimentation and
rifting are contemporaneous so that older sediments are deformed
and faulted as the depression forms and the fill thickens
towards the center of the trough. In the third stage (Fig.
2.6C) basaltic magma, produced by rising upper mantle tempera-
tures, breaks through the Mohorovicic Discontinuity (Moho) and
denser crust. Considerable heat is thereby transferred towards
the surface which produces sediment metamorphism and deforma-
tion, crustal thinning and gravity downfaulting around the
tilted margins of the trough. In the final stage (Fig. 2.6D) a
new, thinner crust of basaltic magma forms closer to the sur-
face. Where the 700°C (1,300°F) isotherm rises into the crust,
granitic basement rocks begin to melt and rhyolite volcanoes
bring up bits of basalt, granite and metamorphosed sediments.
Temperatures sufficient to produce green schist metamorphism are
produced from plumes of hot brine.
The San Andreas Fault System is currently active ,and its
motion continues to produce and expand the "rhomb graben" de-
pressions. As these depressions are formed and continue to
24
-------
B
; MARKER LINES,
ORIGINALLY CONTINUOUS
:-'::'' GAPS BETWEEN BLOCKS
= CENTER LINES IN GAPS
rr: AREA OF OVERLAPPING BLOCKS
50 KILOMETERS
Picture 24
Fxgure 2.4
A and B. Simplified diagram of "rhomb graben
^ana^^ ^ Mult±ple ,,rhomb graben" formation
(Garfunkel, 1972a)
25
-------
Figure 2.5 Tectonic setting of the Gulf of California.
(Garfunkel, 1972a)
-------
Reference Points
B
UPLIFT AND
R ^EXTENSION ' -'
RISING GEOTHERMS
BASALT MAGMA RISING
RHYOLITE. MAGMATISM
-------
expand, they receive sediments from the Colorado River, local
lakes and streams or the marine environment, depending on their
location and geologic conditions at the time of deposition.
Some areas in the central part of the Salton Trough have accumu-
lated over 6,100m (20,000 ft) of sediments (Biehler, 1964).
Current Tectonic Activity—
.•i Widespread active faulting, seismicity, volcanism, sub-
sidence and anomalous geothermal gradients throughout Imperial
Valley attest to the ongoing tectonism of the area.
First, there is the fumarolic-solfataric activity in the
Obsidian Buttes area near the Salton Sea, which is a common
characteristic for most active geothermal areas in the world.
Second, rapid subsidence, on the order of 1.5 cm/yr (0.6
in /yr), of the entire Imperial Valley is indicative of ongoing
tectonism. The subsidence rates and directions are somewhat
different in different parts of the valley. Geodetic dates by
Lofgren (1974) illustrate this with indications of northward
tilting which reaches a maximum somewhere in the southern half
of the Salton Sea. Third, evidence from trilateration surveys
and Lofgren"s geodetic data show that active faulting does exist
in the Salton Sea Buttes area and can be extended backwards in
time by examination of Kelley and Soske's (1936) ground magne-
tometer survey of the area (Fig. 2.7). Unlike the aerpmagnetic
data of the area (Griscom and Muffler, 1971), which loses
some resolution due to the filtering effect of airplane height,
the ground magnetometer survey provides rich detail of the
shallow subsurface. Examination of that map (Fig. 2.7) shows
clear evidence of faulting and right-lateral displacement
through the Red Hill volcano, named as the Red Hill Fault on the
map. There is clear evidence for a displacement of about
0.5 to 0.8km(0.3 to 0.5ml) along the Red Hill Fault at conjugate
points A-A' and less certain evidence for right-lateral dis-
placement of conjugate points B-B1 of about 2.3 km (1.4 mi).
Such offsets are explained in terms of transcurrent faulting of
a geologic structure subsequent to its formation. If we'assume
a constant rate of displacement on the Red Hill Fault, then
these two offsets represent two epochs of volcanism. The
reported age of one of the volcanoes, at 16,000 to 55,000 years
(Muffler and White, 1968) provides a means for assessing the
date of movement on the Red Hill Fault. Assuming a mean age for
the Red Hill volcano of 36,000 ± 20,000 years and that the
displacement of 0.5 km (0.3 mi) occurred subsequent to the
formation of the Red Hill Fault, movement would be on the order
of 1.4 ± 0.4 cm/yr (0.55 ± 0.16 in /yr). This value is within
the same order of magnitude as the present-day movement of 0.5
cm/yr (0.2 in /yr) determined by Lofgren (1974). Lofgren (1974)
ascribes the displacement to movement on the Brawley Fault,
which was the only known fault at the time. We tend to believe
that the movement might have occurred along the Red Hill Fault.
A much tighter trilateration network is needed to resolve that
28
-------
N)
33'IS'-
3S*I2'SO"-
33°IO'
CONTOUR VALUES IN GAMMAS
(MILES)
Figure 2.7 Structural interpretation of a ground magnetometer survey
by Kelley and Soske (1936). (Meidav, et al. 1976)
-------
question. Likewise, the larger postulated displacement of 2.3
km (1.4 mi) along conjugate points B-B1 is likely to represent
an older event of plutonism in the area. Assuming an average
movement of 1.4 + 0.4 cm/yr (0.55 + 0.16 in /yr), the earlier
plutonism in the Red Hill region (possibly one that gave rise to
the entire Salton Buttes stock) took place 170,000 + 50,000
years ago. Robinson, et al. (1976) have presented mineralogical
evidence supporting the theory of more than one cycle of
•volcanism.
Randall (1974) supports the hypothesis of at least two
epochs of heat flow activity in the region, based upon analysis
of the isothermal contour maps of the Salton Sea geothermal
field. According to Randall, the shape of the isothermal pat-
terns and its evident relationship to the most recent cycle of
volcanism (about 16,000 years ago) suggest that the presently
known Salton Sea geothermal field is defined by the spatial
position and location of the intrusive mass, rather than by the
presence or absence of a cap rock or any cpnvective circulation.
Randall further theorizes that the geologic event that resulted
in the formation of the Salton Sea geothermal anomaly and the
volcanic domes happened so recently, geologically speaking, that
insufficient time has elapsed for the local lithologic and
structural variation to significantly affect the shape of the
isotherms that define the thermal anomaly. These conclusions
were based on the limited areal and depth extent of the drill
hole data available for analysis. Data from Meidav, et al.
(1976), while not in disagreement with Randall's data as regards
the shallow, very high temperature regime of the Salton Sea
volcanic domes area, suggests that broader geothermal anomalies
may extend into the area well beyond the high temperature,
elliptically shaped Salton Sea anomaly. From the analysis of
electric log data, Randall has constructed a map of depth to the
top of a metamorphic zone which has been encountered in most of
the wells drilled in the area. Shales in the sedimentary strata
change into low -grade metamorphic rocks as a result of the
application of high temperatures. The metamorphosed surface
conforms in shape to many of the isothermal surfaces, and it
probably serves as a cap rock for the higher temperature reser-
voir in the area.
The inability to correlate individual beds from well to
well Randall attributed to the presence of a large number of
faults in the area. This finding is supported by the previously
reported marine acoustic survey in the Salton Sea (Meidav, 1968)
and further corroborated by Meidav, et al. (1976). Randall's
evidence is also discussed in Section 2.3.3, "Structure of the
Imperial Valley."
30
-------
2.3.3 Structure of the Imperial Valley
The Imperial Valley is a broad structural and topographic
depression. It has steep step-faulted basement margins and
prominent mountain ranges on both the east and west. The broad,
relatively flat basement floor is 6 to 7 km (3.7 to 4.3 mi) deep
(Elders, et al.,1972), and according to Biehler (1964) it lies
Beneath more than 6,100 m (20,000 ft) of marine and nonmarine
^sediments. The areal distribution of the rocks on the mountain-
ous margins and the sediments within the valley are shown on the
geologic map (Plate 2.1). Numerous right-lateral strike-slip
faults extend through the valley; the great majority are compo-
nents of the San Andreas Fault System and most of them trend
northwest (Dibblee, 1954). Three major fault zones of the San
Andreas Fault System in Imperial Valley are, from northeast to
southwest, the San Andreas Fault Zone (Plate 2.2, No. 28 through
36a) located on the northeast side of Imperial Valley, the San
Jacinto Fault Zone (Plate 2.2, No. 2 through 11) in the south-
western portion of Imperial Valley and the Elsinore Fault Zone
(Plate 2.2, 12 through 15) in the southwestern portion of
Imperial Valley. In addition, this study refers to another
fracture zone, herein called the Salton Trough Fault Zone (Plate
2.2, No. 17 through 27), lying between the San Andreas and San
Jacinto Fault Zones. All of these faults and the sediment
structure in Imperial Valley are discussed in more detail below.
Faults—
The major structural trends in Imperial Valley are the San.
Andreas, the San Jacinto and the Elsinore Fault Zones, and a
number of newly discovered and inferred faults which occur in
the alluvial areas in the central part of the valley. This
latter area, between the mapped traces of the San Jacinto Fault
Zone and the San Andreas Fault Zone, will be referred to as the
"Salton Trough Fault Zone" in this report.
All of the faults in these four zones are components of the
San Andreas Fault System, which generally trends north-northwest
and exhibits right-lateral displacement. Numerous smaller
east-northeast trending faults have been mapped in the Penin-
sular Range to the west (Dibblee, 1954), in the mountains to the
northeast (Jennings, 1975; Sylvester and Smith, 1976) and
recently within the valley itself (Meidav, et al., 1976). Left-
lateral displacement has been noted on some of these east-
northeast trending faults.
There are different representations of the number, amount
and length of fault traces proposed in Imperial Valley (Loeltz
et al., 1975; Rogers, 1965; Strand, 1962; Jennings, 1967;
Jennings, 1975; Dutcher, et al.,1972; many proprietary reports
and other publications). Most of the published fault maps of
Imperial Valley represent a generalized picture of fault traces;
in reality the picture may be considerably more complex than
31
-------
presented on these maps. Many of the fault locations are based
on geophysical evidence, some on field mapping, and some on
remote sensing techniques. The trend to date has been that as
more detailed work is done in an area, more complex fault struc-
tures become apparent. For example, after detailed resistivity
studies were conducted just south of the Salton Sea, many more
faults were discovered than had been previously identified (Fig.
2.8) (Meidav, et al., 1976). It is felt that with sufficiently
detailed investigation similar fault occurrences may be dis-
covered throughout the Salton Trough Fault Zone and in other
parts of the valley. Dibblee (1954) considers the San Jacinto
Fault Zone more complex than the San Andreas, and the Elsinore
Fault Zone more complex than the San Jacinto. The concealed
faults of the Salton Trough Fault Zone may turn out to be as
complicated as any of these other zones, but it would have been
impossible for Dibblee to detect the myriad occurrence of con-
cealed faults in the Salton Trough Fault Zone in his field
mapping and to compare its complexity with the others.
The occurrence of faults plays an extremely important role
in geothermal development. For example, faults may provide
structural control for the location of geothermal fields, they
may provide conduits for the lateral and vertical flow of geo-
thermal fluids and fresh ground water, and they can act as
aguitards or aquicludes in the hydrologic system. Since the
occurrence of faults can play an important role in the total
geothermal and hydrologic system, it is important to clarify and
update the existing knowledge about occurrence of faults in
Imperial Valley. To do this, a comprehensive fault map was
prepared for this study (Plate 2.2). This map is a compilation
of fault traces shown in various published maps and includes the
most recent data. A table keyed to the map (Table 2.1) provides
references for fault locations, discrepant fault locations, most
recent fault movement and evidence of faulting. This map and
table provide one of the more comprehensive reviews of faults in
the Imperial Valley that has been published to date.
The San Andreas Fault Zone—
The San Andreas Fault (Plate 2.2, No. 28 and 28a) is traced
from the Durmid area (Plate 2.1), on the northeast shore of the
Salton Sea, southeastward to the international boundary. North
of the study area the San Andreas splays into two segments
called the Banning and Mission Creek Faults. Some faults termi-
nating at the Mission Creek Fault show evidence of left-lateral
displacement (Jennings, 1975). Just north of the study area,
the Banning and Mission Creek segments come together into one
Z°5eofaf the Barmin9-Mission Creek Fault (Plate 2.2, No. 36
and 36a). A complex of subparallel branches of the San Andreas
Fault occurs in a, zone 8 to 16 km (5 to 10 mi) wide extending
v*?^v p^1? ?U1iS area to the north end of the Coachella
Valley. Right-lateral separation of drainage and vertical sep-
aration (northeast side upthrown) of approximately 1,000 m (3,300
ft) are observable along the fault in this area (Babcock, 1969).
32
-------
NO. FAULT NAME
1 Unnamed - along north-
west edge of Salton Sea
la Unnamed - short segment
on eastern edge of
Santa Rosa Mountains
Ib Unnamed - short seg-
ments In various
locations
2 Clark Fault
3 San Felipe Hills
Fault
4 Unnamed - near San
Felipe Hills Fault
5 Unnamed - approx.
same trace as 3
6 Coyote Creek Fault
7 Superstition Mtn.
Fault
7a San Jaclnto Fault
TABLE 2.1 FAULT MAP REFERENCE
FAULT ZONE REFERENCE EVIDENCE
MOST RECENT
MOVEMENT
REMARKS
Indeterminate Jennings, 1975 Abrupt rise In Pre-Quaternary
topography
Indeterminate Jennings, 1975
Indeterminate, Jennings, 1975
unless obvious
alignment with
specific fault
or zone
San Jaclnto Jennings, 1975
San Jaclnto Jennings, 1975
San Jacinto Jennings, 1975
San Jaclnto Loeltz, et al.,
1975
San Jaclnto Jennings, 1975 Surface rup-
ture
San Jaclnto Jennings, 1967
Jennings, 1975
San Jaclnto Loeltz, et al.,
1975
8 Superstition Hills San Jaclnto
Fault
8a Superstition Hills San Jaclnto
Fault
9 Unnamed - approx. San Jaclnto
86 km length on map
10 San Jaclnto Fault San Jacinto
Jennings, 1967 Surface rup-
Jennings, 1975 ture
Loeltz, et al.,
1975
Jennings, 1975
Dutcher, et al.
1972
(c-ontinued)
Quaternary
Quaternary
Quaternary
Pre-Quaternary
Quaternary
1968
Quaternary
Quaternary,
1951, 1965,
1968, 1969
Pre-Quaternary,
Quaternary (?)
Quaternary
Breaks probably occurred during
Borrego Mtn. Earthquake of 1968.
Mapped along Jennings, 1975,
Superstition Mtn. Fault. Blends
with Coyote Creek Fault to north-
west.
Less southern extension than 9,
slightly more northern extension.
Agrees with 10, Dutcher, et al.,
1972, except Jennings, 1975, con-
siders trace concealed.
This reference considers trace
above international border as
approximately located though
queried.
-------
NO^ FAULT NAME
11 Unnamed - approx.
32 km length on map
12 Elsinore
13 Laguna Salada
13a Elsinore
14 Elsinore
15 Unnamed - queried
segment between
Laguna Salada (13,13a)
and Elsinore (12)
Faults
TABLE 2.1 (continued)
FAULT ZONE REFERENCE EVIDENCE
San Jaclnto
Elsinore
Elsinore
Elsinore
Elsinore
Elsinore
HOST RECENT
MOVEMENT
Pre-Qua ternary,
1969
Jennings, 1975 Short segment
had creep trig-
gered by earth-
quake with epi-
center along
Imperial Fault
69
Jennings, 1975 Surface rupture Quaternary
Strand, 1962
Jennings, 1975
Lomnitz, et al.
1970
Dutcher, et al.
1972
Jennings, 1975
Quaternary
Some microseis-
mic activity
Pre-Quaternary
REMARKS
Originally mapped by Dibblee,
1954.
Westernmost fault zone of San
Andreas System.
Extends into Elsinore (14)
Fault in northern Mexico.
Same trace ae 13, different in
name only.
Merges into Laguna Salada Fault
as trace mapped northward.
16 Imperial Fault
16a Imperial Fault
San Jacinto
or transition
between SJ &
Salton Trough
same as above
Jennings, 1975 Surface rup- 1940, 1966, 1968, Also associated earthquake swarm
tures, micro- 1971 along 15 km Just north of border
seismic activity in June 1973 (Hill, et al., 1975).
Strand, 1962
Jennings, 1967
Loeltz, et al.,
1975
1940, 1966, 1968, Approximate agreement with 16.
1971
17 Brawley Fault
segment
17a Northward extension
of 17 and two inferred
short transform segments
Salton Trough Sharp, 1976
Salton Trough
Johnson &
Hadley, 1976
Tectonic frac-
ture and dis-
placement,
strike N3°W
Epicenter de-
fined location
during earth-
quake swarm
January &
February 1975
January &
February 1975
Newly recognized segment from
rupture during earthquake swarm
in 1975 (Sharp, 1976), may be
different fault than earlier
recognized 17d.
(continued)
-------
NO. FAULT NAME
17b Probable Brawley Fault
- Salton Sea Area
17c Brawley Fault -
Salton Sea Area
TABLE 2.1 (continued)
MOST RECENT
FAULT ZONE REFERENCE EVIDENCE MOVEMENT
Salton Trough Hill, et al., 1. Microearth-
1975a quake epicenter
Meldav, et al., location
1976 2. Electrical
resistivity data
Salton Trough Randall, 1974 StratIgraphlc
correlation
between we]Is
REMARKS
OJ
Ln
17d Brawley - trace
through Imperial
Valley
18 Unnamed - between
Brawley & Calipatrla
18a Red Hill
18b Unnamed - very dost
to Red Hill
Salton Trough Jennings, 1975 Quaternary
Salton Trough Jennings, 1975 Quaternary
Salton Trough Meidav, et al., Electrical Quaternary
1976 resistivity
data, possible
surface displace-
ment at Red Hill
Volcano
Salton Trough Randall, 1974 Borehole strati-
graphic corre-
1 at ion
Approximate agreement with Red
Hill Fault of Meidav, et al.,
1976.
Also supported by structural
interpretation of ground magne-
tometer survey by Kelley & Soske,
1936.
19 Calipatria
19a Calipatria
19b Unnamed - close
to Calipatria traces
Salton Trough Meidav,
Electrical re-
et al., 1976 sistivity data,
also alignment
of thermal
springs through
Mullet Island
Salton Trough Jennings, 1975
Quaternary
Salton Trough Randall, 1974 Borehole strati-
graphic corre-
lation
Main trace runs north from Inter-
national border, secondary splay
occurs north of Calipatria, both
traces end in Salton Sea.
Four probable traces In approxi-
mate area of 18, 19, and 19a.
20 Ulster
21 Westmorland
22 Fondo
Salton Trough Meidav,
Electrical re-
et al., 1976 sistlvlty data
Salton Trough Meidav,
et al., 1976
Salton Trough Meidav,
Electrical re-
sistivity data
Electrical re-
et al., 1976 sistivlty data
(continued)
-------
NO. FAULT NAME
TABLE 2.1 (conl-inued)
FAULT ZONE REFERENCE EVIDENCE
MOST RECENT
MOVEMENT
REMARKS
23 Transform Faults,
AA through GC
24 Sal ton Sea Faults
or discontinuities
Salton Trough Meidav, Electrical re-
et al., 1976 slstlvlty data
Salton Trough Meldav, 1968 Sparker Survey
Dashed lines probable fault
or discontinuity.
OJ
25 Mesa Fault
26 Holtville and short
parallel trace to
east
27 Unnamed in East Mesa
Area, 27 km long
28 San Andreas
28a San Andreas
29 Unnamed - of 30 km
length through Dunes
KCRA
Salton Trough Combs & Geophysical
Hadley, 1977 Study
Salton Trough Babcock, 1971 Infra-red
aerial photo-
graphy, possible
surface displace-
ment
Salton Trough Rex, 1970
San Andreas
San Andreas
San Andreas
Geophysical
Strand, 1962
Jennings, 1967
Loeltz, et al.,
1975
Loeltz, et al.,
1975
Roughly parallel, but slightly
west of 19a.
30 Algodones Fault
San Andreas Jennings, 1975 Possible surface
rupture in West
Yuma Mesa area,
to southwest
30a Algodones Fault San Andreas
30b Unnamed - between
Algodones Fault
(30a) and Sand Hills
Fault (30d)
30c Algodones Fault San Andreas
Loeltz, et
al., 1975
San Andreas Jennings, 1967
Olmsted, et
al., 1973
Gravity, aero-
magnetic, elec-
trical resistivity
and seismic surveys,
also borehole stra-
tigraphic correla-
tion
Based on work done In West Yuma
area.
30d Sand Hills Fault
San Andreas
Jennings, 1975
(continued)
-------
TABLE 2.1 (continued)
SO. FAULT NAME FAULT ZONE
31 San Andreas and San Andreas
associated splays
along NE shore of
Salton Sea
32 Hidden Springs Fault San Andreas
33 Powerltne Fault San Andreas
34 Unnamed - parallel San Andreas
and northeast of
Powerllne Fault
35 Hot Springs Fault San Andreas
36 Banning-Mlsslon Creek San Andreas
Fault
REFERENCE EVIDENCE
Jennings, 1975
Hays, 1957,
Jennings, 1967
Jennings, 1975
Babcock, 1969
Jennings, 1975
Babcock, 1969 Gravity Survey
Jennings, 1975
Babcock, 1969
Jennings, 1975
Loeltz, et
al., 1975
MOST RECENT
MOVEMENT REMARKS
Quaternary, creep-
triggered by
earthquakes along
other faults
Quaternary?
Quaternary?
Quaternary?
Observed creep, Quaternary
surface dis-
placement
No surface expression except
one location of seeps.
36a Bannlng-Mlssion Creek San Andreas
and associated splays
Jennings, 1967
-------
Vertical separation on the Hidden Springs and Powerline Faults
created a horst between each of these faults and the San Andreas
Fault (Babcock, 1974).
The Hidden Springs Fault (Plate 2.2, No. 32) was mapped in
the Mecca Hills (Fig. 2.1), north of the Durmid Hills, by Hays
(1957). This fault in the Durmid Hills area is marked by a
scarp near the Coachella Canal and by alignment of springs. The
Hot Springs Fault (Plate 2.2, No. 35) location is indicated by
alignment of hot springs. The trace of the Powerline Fault
(Plate 2.2, No. 33) is marked by permeable sandy beds, uplifted
on the southwest side of the fault, and by lake silt on the
downthrown, northeast side. Springs are also found along this
trace. Two gravity profiles run by Babcock (1969) revealed a
buried fault east of the Powerline Fault and roughly parallel
with it. Ground water seeps are found in one area of this
inferred fault.
The southern segment of the San Andreas Fault has a fairly
low rate of seismic activity (Allen, et al. 1972). Brune and
Allen (1967) conducted a regional survey to measure microearth-
quake frequency and distribution in the Salton Trough. Virtu-
ally no microearthquakes occurred between Desert Hot Springs
(Fig. 2.1) and the Mexican border. However, the fault traces
along the northeastern margin of the Salton Sea are so distinct
in the field that displacement must have occurred in very recent
time (Sharp, 1972). Allen, et al. (1972) report slightly eroded
small scarplets as much as 50 cm (20 in high along this seg-
ment. The Borrego Mountain earthquake of April 9, 1968, the
epicenter of which was about 50 km (31 mi) to the west, is also
known to have triggered fault creep in this segment of the San
Andreas Fault.
Surface expression of the San Andreas Fault dies out south-
east of the Durmid area. The main fault trace itself is not
evident south of Bombay Beach and is believed to splay to the
west and south into numerous parallel and subparallel segments.
Geomorphic expression of the fault is hidden by Pleistocene
Lake Cahuilla sediments and Quaternary alluvium. It is also
possible that the San Andreas Fault has transferred its locus of
energy release to traces to the west. This possible mechanism
is discussed in more detail in the Salton Trough Fault Zone
subsection below. The existence of the San Andreas on the
northeast side of the Imperial Valley is inferred from gravity
data (Biehler, 1964),and the location of its trace south of the
Salton Sea is not precisely known (Sylvester and Smith, 1976).
Seismic refraction profiles at the northeast margin of the Sand
Hills reveal the probable trace of the Algodones Fault (part of
the San Andreas Fault Zone) (Plate 2.2, No. 30, 30a and 30c)
which extends southeast to the Yuma area (Olmsted et al 1973).
wni°UiSQ???PhySiCaKSKtUdieS ,
-------
the Sand Hills and are named the Sand Hills Fault (Plate 2 2
No. 30d). " '
San Jacinto Fault Zone—
A number of locally active discontinuous traces of the San
Jacinto Fault Zone (Plate 2.2, No. 2 through 11) enter the
valley from the northwest, paralleling the trend of the San
Andreas Fault System. The fault zone enters the trough as two
/pain strands and is about 10 km (6 mi) wide. The Clark Fault
tPlate 2.2, No. 2) is on the north and extends through Clark
Valley and along the southern tip of the Santa Rosa Mountains.
A small trace (Plate 2.2, No. 5) lies along the western part of
Clark Valley and extends southward from the Clark Fault into the
Borrego Badlands, where it disappears under alluvium or dies
out. The second strand, the Coyote Creek Fault (Plate 2.2, No.
6), is the southernmost trace. The Superstition Mountain Fault
(Plate 2.2, No. 7) and Superstition Hills Fault (Plate 2.2, No.
8) are southeastward projections of these two strands. The
Imperial Fault (Plate 2.2, No. 16 and 16a), as represented by
fracturing during the 1940 Imperial Valley earthquake (M = 7.0),
may also belong to the San Jacinto Fault Zone. This fault, if
projected northwest, aligns with the Clark Fault and the two
could join at depth (Sharp, 1967). The San Felipe Hills Fault
(Plate 2.2, No. 3) lies approximately along this trend, too.
Twenty-four kilometers (15 mi) of right-lateral separation have
been noted on the San Jacinto Fault (Plate 2.2, No- 7a) in the
Peninsular Range northwest of the Salton Trough (Sharp, 1967).
Five kilometers (3 mi) of this slip has been along the Coyote
Creek Fault. This fault has breaks with vertical components
which show separations in excess of 1 km (0.6 mi).
On April 9, 1968, a magnitude 6.4 shock occurred near
Borrego Mountain, in northwestern Imperial Valley (Allen, et al.,
1968). Right-lateral surface displacement accompanied the
earthquake along several strands within the complex San Jacinto
Fault Zone. The Coyote Creek Fault moved a maximum of 38 cm (15
in). Smaller surficial offsets occurred along the Superstition
Hills Fault and Imperial Fault. Previous to this movement,
offset gullies, displaced alluvium and fault scarps gave evi-
dence of the relatively recent activity in this zone. Minor,
vertical northeast trending cross faults occur in the Borrego
Badlands and Superstition Hills. Drag folds associated with
these cross faults suggest left-lateral displacement (Dibblee,
1954).
Elsinore Fault Zone—
The most southwesterly fault zone in Imperial Valley is the
Elsinore Fault Zone (Plate 2.2, No. 12 through 15). It extends
southeastward from the Peninsular Range into the Salton Trough
near the Tierra Blanca Mountains (Fig. 2.1) and continues into
Mexico as the Laguna Salada Fault. Continuity of the Elsinore
Fault (Plate 2.2, No. 12, 13a and 14) to the Laguna Salada Fault
(Plate 2.2, No. 13) can be established by the steep gravity
39
-------
gradient traced northwest to the Elsinore Fault along the west
side of the Cucapas Mountains in northern Mexico. It is a dis-
tinct, but discontinuous, zone of surficial fractures. Continu-
ity between these strands cannot always be demonstrated because
they may be hidden by overlying, recent alluvial deposits. The
strike-slip offset along this zone is small compared with dis-
placement estimated on the San Jacinto and San Andreas Fault
Zones (Sharp, 1967). Local vertical displacement along the
Elsinore Fault is significant. Over 900 m (2,950 ft) of dip-
slip movement has been observed on this fault northwest of the
valley (Jahns, 1954). However, Dibblee (1954) points out that
the fault movement has been twice reversed so the displacement
may be more apparent than real. Right-lateral movement is
indicated by drag folds in Cenozoic sediments (Dibblee, 1954),
but the actual amount of displacement is unknown. It could be
several times that of the dip-slip displacement.
Historic movement in the Elsinore Fault Zone has not been
documented , and within the Salton Trough only the segment south
of the international boundary has demonstrated appreciable
seismicity in recent times (Sharp, 1972).
Lateral shear or torsion between the Elsinore and San
Jacinto Faults is probably responsible for the many fault blocks
and shattered plutonic rocks in the Vallecito and Fish Creek
Mountains, on the western border of Imperial Valley. These
mountains contain many northeast trending, steeply dipping normal
faults (Plate 2.2, No. 16), most with the northwest sides up.
The Coyote Mountains consist of northward tilted, upended meta-
sediments elevated along the Elsinore Fault.
Salton Trough Fault Zone —
The Salton Trough Fault Zone includes the faults numbered
17 through 27 on Plate 2.2. The great majority of these faults
show no surficial expression and have been located by - geo-
physical methods.
A regional resistivity survey in Imperial Valley resulted
in the discovery of two major faults which run from south of
Brawley to the Salton Sea area (Meidav and Rex, 1970). These
faults first appeared in the literature on maps by Rex (1970)
and were named the Brawley and Calipatria Faults (Plate 2.2, No.lTb,
17c and 17d and 19 and 19a, respectively) . Later gravity surveys
confirmed the presence of large vertical displacements beneath
the valley alluvium. However, both surveys were inconclusive in
demonstrating the continuity of major fault zones in the
southern part of the trough.
- Four additional faults striking about N45°W are inferred
£;2S U^^l^l SUre^ of the Salton Sea geothermal field.
They are the Westmorland, Fondo, Red Hill and Wister Faults
40
-------
(Plate 2.2, No. 21, 22, 18a and 20 respectively) (Meidav, et al.,
1976) (Figure 2.8). Transverse discontinuities (Plate 2.2, No.
23) occur between the six faults, trending northeast into the
Salton Sea, but they could also have more of an east-west sense
than a northeast-southwest sense. It is felt that the discovery
of these faults is typical of the complex structure that may be
found with additional detailed resistivity surveys in other
parts of Imperial Valley. The Westmorland and Red Hill Faults
are major aquicludes in the Salton Sea geothermal field.
However, all of the faults along the southeastern shore of the
sea may behave as aquitards separating the hypersaline brines
indicative of the Salton Sea geothermal area from the less
saline water outside the volcanic field. The Red Hill Fault,
confirmed by a ground magnetometer survey (Kelley and Soske,
1936), also shows evidence of right-lateral displacement through
the Red Hill Volcano.
Five volcanic domes, extruded onto valley floor sediments
between 16,000 and 55,000 years ago (Muffler and White, I968a),
lie along a northeast trending line on the southern edge of the
Salton Sea. If the Salton Sea area is the northernmost spread-
ing center of the landward extension of the East Pacific Rise,
then the volcanism, high heat flows, symmetrical magnetic anom-
alies and transform faults are logical expressions of this
activity. The discovery of the six aforementioned faults just
south of the Salton Sea (Fig. 2.8) and the absence of seismicity
or gravitational expressions of the San Andreas Fault south of
Bombay Beach tend to support the hypothesis implied by Elders,
et al. (1972) that the Salton Sea volcanic field is the locus
of transfer of energy release and fault activity from the San
Andreas Fault southwestward to the Salton Trough Fault Zone.
The Brawley earthquake swarm of 1975 (Sharp, 1976; Johnson
and Hadley, 1976) produced displacement along a 10.5 km (6.5 mi)
fault segment (Plate 2.2, No. 17) that branches northward from
the Imperial Fault, about 8 km (5 mi) east-northeast of El
Centre. Movement at the surface was apparently vertical and
reached a maximum of more than 0.2 m (0.7 ft) at one road in the
area. En-echelon cracking implied a developing right-lateral
component, but no major structures were laterally offset by the
faulting. This trace was called the Brawley Fault, but it has a
distinctly different location than the Brawley Fault traces
(Plate 2.2, No. 17a through 17d) previously identified by geo-
physical methods. However, the original fault location by
electrical and gravity surveys had no control in the southern
portion of Imperial Valley, so this newer trace may define the
actual trace of the Brawley Fault or perhaps represents the
trace of a different fault.
The general trend of the rupture zone, as well as the trace
of the older movements along the Brawley Fault (No. 17), is
41
-------
EXPLANATION
FAULT LOCATION BASED ON ELEC-
.» TRICAL RESISTIVITY SURVEY
where cant inuot ion uncertain)
/vrv DEEP FAULT "1
Structural ftaturai
--- PROBABLE FAULT 1 In Solton S«o
TRACE } located by iporker
I survey (Meidav, 1968)
—I—I- QUESTIONABLE
FAULT TRACE J
OR SLUMP
VERTICAL ELECTRICAL DEPTH
SOUNDING LOCATION
ftX\ \ \A |X\ \ >N
^XTTTT- *••
(milet) i
2345 I
i ' i ' .' 1 I
24681
-JS'OO'
Figure 2.8 Map of possible faults and discontinuities in the
Salton Sea area. (Meidav, et al.,1976)
42
-------
about N3°W. The strike of the long axis of the swarm's epi-
center pattern was N8°W. Two short northeast trending normal
faults, showing left-lateral rotational cracking at the surface,
were inferred by epicentral location. Savage, et al. (1974)
report that fault slip has possibly occurred since 1934 on the
Brawley Fault (No. 17d), near the southeast end of the Salton
Sea, about 24 km (15 mi) north of the town of Brawley. But it
has not been conclusively demonstrated whether faulting there is
directly contiguous with the zone of movement to the south
reported by Sharp (1976).
The Holtville Fault (Plate 2.2, No. 26) (Babcock, 1971)
trends southeast and is approximately 11 km (6.8 mi) long. Its
location is inferred from low angle infrared aerial photography
and offset in man-made structures, notably 2 m (7 ft) of short-
ening of the concrete runway at the Holtville airport. Babcock
specifies that without ground evidence the infrared photos do
not conclusively prove faulting because trends in the area can
also be shorelines of ancient Lake Cahuilla. It is also pos-
sible that shortening in the Holtville airport runway may be due
to compressional buckling caused by near surface subsidence.
During a five-week period, in the summer of 1973, locations
were determined for 36 microearthquakes having epicenters within
the 155 sq km (60 sq mi) areal extent of the Mesa geothermal
anomaly (Combs and Hadley, 1977). Epicenter and focal depth
determinations defined a newly located right-lateral strike-slip
fault, the Mesa Fault (Plate 2.2, No. 25). First motion studies
indicated strike-slip faulting although there is no surface
expression of this fault. The northwest-southeast trending Mesa
Fault (Plate 2.2, No. 25) probably acts as a conduit for rising
geothermal fluids of the Mesa geothermal anomaly.
Six right-lateral strike-slip faults (Plate 2.2, No. 17c,
18b,.19d, 17b, 18a and 19) were inferred southeast of the Salton
Sea through studies of borehole cuttings and electric log data
from 16 holes (Randall, 1974). Randall (1974) made approximate
subsurface stratigraphic correlations from borehole to borehole
using a characteristic shale and sandstone marker horizon. He
states that he drew these inferred faults parallel to the San
Andreas Fault trend. Using the southwesternmost well as a pivot
point, these structures have been redrawn on the fault map
(Plate 2.2) generally parallel to the Jennings (1975) trend of
the San Andreas along the northeast shore of the Salton Sea.
These replotted traces of Randall's inferred faults correspond
fairly well to the Brawley, Red Hill, and Calipatria traces of
Meidav, et al. (1976).
Sediment Structure—
Sediment structure in Imperial Valley is relatively compli-
cated. The basement complex is composed of both the plutonic
43
-------
rocks of early and late Mesozoic age and the Precambrian to
Mesozoic metamorphic rocks which they intrude (Bushee, et al.,
1963). Overlying this pre-Tertiary basement complex is a thick
sequence of dominantly nonmarine sedimentary rocks which range
in age from Eocene to Holocene. The depth-to-bedrpck map (Fig.
2.9) shows the areal distribution of sediment thickness. The
contours show the greatest thickness of over 6,100 m (20,000 ft)
in the central part of the valley south of the Salton Sea. The
bedrock surface generally defines a roughly ellipsoid-shaped
surface with a northwest-southeast trending major axis. Sharp
discontinuities of the bedrock surface occur where it is offset
by major faults. Generally the sediments lower in the section
show more deformation since they have been exposed to the con-
tinuing tectonic movements of the Salton Trough for a longer
period of time.
The development of the Salton Trough in the late Cenozoic
has involved folding and warping in addition to faulting. Most
of the folding is related to major fault activity and indicates
right-lateral drag. Some folding is unrelated or indirectly
related to the faulting / and these folds are not as tight as
those near faults (Loeltz, et al.,1975). Dibblee (1954) noted
much tight right-lateral drag folding near and related to fault-
ing and that the folds become broader further from the fault.
Folding of sediments in Imperial Valley is more intense
than the mild deformation, mainly warping, seen in upper Ter-
tiary and Quaternary nonmarine deposits along the Colorado River
immediately to the east (Metzger, et al., 1974). The sediments
throughout the trough display a number of intermediate and small-
scale folds, as well as homoclinal dips over large areas.
The pattern of modern sedimentary accumulation and the
beginning of anticlinal hills on the southwest side of the
valley reflect continuing diastrophism in the trough. The
basement floor probably once showed much relief, but progressive
diastrophism and erosion have allowed youngest to oldest sedi-
ments to lie directly upon the basement floor. Localized intra-
formational unconformities are also fairly common. There is
little lateral continuity, especially as evidenced along the
margins of the trough within the coarser detritus and lacustrine
beds. However, in the axial parts of the trough, sediments are
almost uniformly fine grained. Flanks of the trough show wide-
spread instability, marked by erosional truncation of thick
sections of sediment that probably accumulated since Pleistocene
time (Sharp, 1972). This detritus has perhaps been redeposited
beneath the Salton Sea, or elsewhere in the axial part of the
basin, suggesting continuous subsidence within the axial part of
the trough. *
The only completely exposed Cenozoic sequence is a south-
west dipping homocline in the southwestern portion of Imperial
44
-------
Ul
EXPLANATION
OUTCROP
CONTOUR INTERVAL = 5000 ft
0 5 10 15 20 25
kilometers)
Figure 2.9 Depth to basement complex, Imperial Valley, California. (Rex, 1970)
-------
Valley on the north side of Carrizo Valley. The Tertiary sedi-
ments on the south side of the Elsinore Fault are upended and
show intense folding (Dibblee, 1954). Further details of anti-
clinal and synclinal structures, faults and folds associated
with specific physiographic features in the mountains to the
west of and on the west side of the valley are detailed by
Dibblee (1954). In the northwest part of the valley these
features can be observed in Cenozoic exposures in the Supersti-
tion Hills and Santa Rosa Mountains. Prominant folding, includ-
ing overturning and isoclinal folding, occurs in linear belts
adjacent to fault zones, as seen in the Mecca Hills and Ocotillo
Badlands (Sharp and Clark, 1972).
Historic seismicity within the valley would suggest con-
tinuing deformations within the trough sediments. Meidav (1969)
reported that the upper water-bearing deposits in the valley dip
slightly southward. Furthermore, warping is suggested on the
west side of the trough by the Lake Cahuilla shorelines which
are tilted southeast, and by one strand on the east side which
is tilted northwest.
2.3.4 Stratigraphy and Lithology of Salton Trough Rocks
The Salton Trough has been filled with late Tertiary del-
taic and lacustrine sands, silts and gravels overlain by Qua-
ternary alluvium and lake sediments. These deposits have a
maximum measured depth of 6,100 m (20,000 ft) (Biehler, et al.,
1964; Babcock, 1969) to the pre-Tertiary granite and metamorphic
basement complex (Fig. 2.9).
Rocks of the Salton Trough range in age from Precambrian
basement complex to Recent alluvium and dune sands, and corre-
spondingly from dense, competent, hard rocks to totally uncon-
solidated sedimentary deposits. Most of the central Imperial
Valley fill is Pliocene and younger; none is older than mid-
Miocene, and rocks as old as Eocene only occur in the bordering
mountains (Durham, 1954, p. 27). One deep well, near Brawley,
was drilled through more than 4,000 km (13,000 ft) of interbed-
ded, fine-grained sandstone and siltstone (Muffler and Doe,
1968). The most complete stratigraphic section, consisting of
more than 5,500 m (18,000 ft) of sediments, is exposed from
Split Mountain Gorge to Carrizo Wash (Garfunkel, 1972b). Hydro-
logically, the younger and nearer-surface sedimentary units play
a much more important role in the ground water flow system and
will therefore be emphasized.
The Cenozoic sedimentary rocks in Imperial Valley have been
divided into three major categories by the California Department
of Water Resources (1970). The lower (oldest) unit consists of
early to mid-Tertiary, mainly nonmarine sedimentary rocks with
some volcanic and marine sediments. The middle unit is the late
Tertiary Imperial Formation claystone and sandstone of marine
46
-------
origin. The upper (youngest) unit is the Pliocene or Quaternary
nonmarine clastic, deltaic and lacustrine deposits derived from
Colorado River detritus. The heterogenous deposits of this
upper unit are thousands of meters thick.
The main source of the thick section of Eocene to Holocene
nonmarine sediments in Imperial Valley has been Colorado Plateau
debris transported and deposited by the Colorado River. Some of
these sediments are also from local sources deposited in allu-
vial fans, barrier beaches, lacustrine beds and braided beaches
(Coplen, 1976).
An illustration of the interfingering and lensing nature of
the alternating sand, silt and shale layers is shown on cross
section D-D1 (Fig. 2.10) of average percent volume of sand
bodies in the sedimentary section (Fig. 2.11).
Source areas for each type of sediment can be clearly
identified by their distinctive mineralogies (Van De Kamp, 1973;
Muffler and Doe, 1968). Both types of sediment contain small
amounts of clay and heavy minerals but those from the Colorado
Plateau source area contain 60% to 70% quartz, 20% feldspar, 2%
chert and calcite; while those from local tributary valleys and
basin margins contain 40% to 50% quartz, 30% feldspar, 1% chert
and no calcite. The local deposits exhibit sharp lateral facies
changes (Van De Kamp, 1973) which are attributed to the meander-
ing course of the Colorado River and its tributaries (Coplen,
1976).
Undifferentiated Tertiary volcanic and intrusive rocks of
various ages consisting of local andesite, rhyolite and basaltic
lava flows and tuffs occur within the sedimentary section.
Recent volcanic activity has deposited the Niland Obsidian
(Dibblee, 1954). They are among the youngest rocks in the
valley. Changes in lithology occur at depths greater than 900 m
(3,000 ft), and greenschist facies minerals form at temperatures
above 300°C (597°F) (Muffler and White, 1968b).
Stratigraphic and Lithologic Description of Units—
A brief lithologic description of individual units is pre-
sented below in chronological order, from oldest to youngest.
The areal distribution of these units is shown on the geologic
map of Imperial Valley (Plate 2.1). Fioure 2.12 presents a com-
posite column of the Salton Trough showing inferred time-strati-
graphic relations, estimated maximum thickness and lithology.
In the Mecca Hills area (Fig. 2.1) correlative age relations and
Stratigraphic thicknesses across faults and along strike are
uncertain due to sharp facies changes, absence of marker beds or
fossils and numerous diastems (Sylvester and Smith, 1976).
This cautionary note should be extended to our study area in
Imperial Valley.
47
-------
oo
RIVERSIDE CO
R. II E. R. 12 E. R. 13 E. R. 14 E. R. 15 E. R.I_6E.
" ~ ~
. 17 E. R. 18 E. R.I 9_ E_. R. 20 E. R. 21 E.
~T~ ^EXPLANATIONH
TMJ .18 Ij
IpUMPING-TEST SITE IE ^ S
JNumber refers to LCRP wtll.j g "W^ a
•Initials Identify owners of J | ^^*"
'other wells. See Table 2.2 . | > XVv
•
IPOROSITY PROFILE SITE |
WELL LOCATION
(WELL NUMBER FROM FIGS. I
-T, "217 TO 2 19 (Dutcher.etal., '
°^ (1972)
-------
LOCATION OF SECTION SHOWN ON FIG. 2.10
£>•
VD
• 12,000
HORIZONTAL SCALE
( IN THOUSANDS OF FEET)
0 10 20 30 40
I "-i—'—H r1
0 « « 12
(KILOMETERS)
Figure 2.II Cross section of average percent volume of sand bodies in sedimentary
section. (Randall, 1971)
-------
en
o
I'pi.ermi i^l J.i'iistrine silt.
•,.onl ,uul c I ay in I he cent ra 1
p.ii-l .1) i he \ ul ley WJ thin t t>e
shore 1 Hies ol the lake
c< >r i a and pumi re
3OO FEET MAXIMUM
THICKNESS ABOVE
UNCONFORMITY .
Pnur 1 y conso I i da ( ed hcu 1 der
conn rome rate , Rrad i OK has i n-
wn rd i n 1 < ' sands ( one and c • ] ay-
s t une ( d 1st r i bu r t>d genera I 1 y
in forehay a reas a lonK loot hi I 1 s
fl ay stone, s i 1 t stone , sandstone
JUKI pebbl y grave 1 depos i t s
ft aysione and some sandstone
oI 1 urusr r i nr origin font ains
.1 1 aens t r i ne t anna of minute
mol1usks, ostracods and rare
foritmi n i Tera
The ent i rp series <>( marine'
depos i t s border* ng Carri /.o
Mounta i n , i ne 1 ud i n« c:on(i lomeratt
sandstone, coral Ii ferous 1ime-
stonc some basali f1ows and
(low breccias, siltslonc with
some hard , f ossi 1 i ferou.s J imy
sandstone
Hidpe-rappiHK sequenco ol
lias;i it II ows and f I ow brr-er i as
NI m-rim r i ne sed inw*n I a ry ro<-ks
and i ni ere a I at <•(! urHlesi t i <•
I lows and s il Is
Pyrorlastit: rocks and minor
f I ows o I" a ndes i t i c to rhyo I i t i c
cun I a i UK , Id.ss i 1 -
i I e roiis mj* r i ne clastic rocks ,
ea r I y I o middle Korene ranti-
i up from CM m rse eori^lomeratc
nnd bre<-<- ia in the lower part
to s i 11 s tone and sandst one in
t he upper par I
(Iran i I i c rocks , Pre fret aceous
seh i s i . f-ni • i ss . and 1 imesi one
rjinii i r\K in a^e ( rom MOHO/.D i c
to I're -Cambr i an
• • •
(6000)—-x. . . (7000)^-
N"
' " ' X>-^0*' • ' • -— • „- ° * o
nperial . Q "T^T" . * • T^~ * s. Canebrake
A1 Conalomerate
1 -si >r tetl 1 i m
Ti - • •
- , (40OO) '
^--— * I / C" QTc
^Hl^ . ' ' / . t <9OOO )
•''•-•• 'lj. o
„ Split Mountain Formation / Fish Cn
"-I'-TgTOO^-r- ~* ~-\Tl (1C
Fish Creek Gypsum
(100) ^^
Chocoljlc MoiinUina
Alvefson Andesite Lava
Older volcanic rocks
of Chocolate Mountains
TV if IT
"Unnamed OligoceneO"
•
T»
. (-5000)
O -° -O 'o' . Maniobra Formalio'n • P- f - O ^
o ." o ' -° ' no* on'mop ' '(•*-48OO)" O ' ° c
f 1 uv i a 1 and dc1 I a I c
( o:irse-pr;i i ned H 1 1 uv i al - fan
-------
Pre-Tertiary granitic and metamorphic rocks of the basement
complex lie below an unconformity and are divided into the
following three main units:
1) Pre-Cenozoic granitic and metamorphic rocks consisting
of gneiss, limestone, schist and granite, ranging in
age from Precambrian to Mesozoic.
2) Orocopia Schist, a Precambrian dark grey micaschist,
named by Miller (1944), exposed for many thousands of
meters in the Orocopia Mountains and extending west.
3) Undifferentiated Mesozoic granitic rocks.
The remaining rocks in the section are Cenozoic, with the
greatest thickness being of Pliocene age and younger.
The lower and mid-Eocene Maniobra Formation of Crowell and
Suzuki (1959) consists of about 1,500 m (4,900 ft) of fossilif-
erous marine clastic rocks, ranging from coarse conglomerate and
breccia in the lower section to siltstone and sandstone in the
upper part. It is exposed northwest of the Salton Sea in the
Orocopia Mountains (Fig. 2.1).
The Maniobra Formation is unconformably overlain by about
1,500 m (5,000 ft) of unnamed Oligocene nonmarine sedimentary
rocks (Crowell, 1962, p. 28) in the Orocopia Mountains. These
rocks are part of the "Unnamed Oligocene" of Crowell and Suzuki
(1959) and Durham and Allison (1961) which consists of nonmarine
conglomerate, sandstone, breccia, mudstone and evaporite depos-
its. Rocks of similar composition, which are probably correla-
tive, are also exposed in the Chocolate Mountains northeast of
the valley and in parts of the Peninsular Range, just west of
the valley (Durham and Allison, 1961).
The following three igneous formations have been placed
stratigraphically within the "Unnamed Oligocene" (Loeltz, et al.,
1975) (Fig. 2.12): the older volcanic rocks of the Chocolate
Mountains consisting of pyroclastics and flows of andesitic to
rhyolitic composition; the basaltic andesite or basalt of the
Chocolate Mountains which forms a "ridge capping sequence of
dark grey to dark brown flows and flow breccias" (Loeltz, et al.,
1975); and the Alverson Andesite consisting of upper Miocene
basic andesite lava, breccia and tuff, up to 210 m (700 ft)
thick (Dibblee, 1954). The Alverson Andesite lies above the
lower part of the Split Mountain Formation as defined by Tarbet
and Holman (1944) but below the Split Mountain Formation as
redefined by Woodard (1961) (Loeltz, et al.,1975, p. 9). Nearby
contemporaneous rocks in the Yuma area, and their associated
nonmarine sedimentary formations, are mid-Tertiary in age while
their intruding volcanics are late mid-Tertiary and have been
dated at 23 to 26 million years (Olmsted, et al.,1973).
51
-------
Uppermost lacustrine at 11,
sand, and clay in the central
pan oT the valley within the
shorelines of the lake
Ul
o
Obsidian.
• rI a and pumice
300 FtET MAXIMUM
THICKNESS ABOVE
UNCONFORMITY —
Poorly consolidated boulder
conglomerate, grading basin-
ward into sandstone and clay-
M.>ne, distributed f*en«-rnlly
in forebay areas a long foothi 11
CI aystone, si 11stone. sandstone
and prbbly grave! deposiIs
Claystone and some- sandstone
ol lacustrine origin contains
A I a rust r i tie fauna of mi nut r-
mo! disks, ostrarods and rare
foramini fera
The entire series of marine
deposits bordering Carrizo
Mount a i n, i ncIudi ng conglomera t r
sandstone, cora)1i ferous 1ime-
st«me, some basalt flows and
flow breccias, siltstone with
some hard, fossi1Iferous limy
sandstone
Rldge-capptng sequence of
hnsalt flows and flow breccias
Non-mar i ne sedimentary rr>cks
and i nl «T» a 1 :>t ed andesi ti r-
(lows and sills
Pyroclastic rocks and minor
flows of andesltic to rhyolitic
romposi t ion
Orncopia Mountains, fossil-
i fcrotis marine clastic rock.s,
early to middle f-locene, ranR-
inR from coarse conglomerate
and breccia in the lower part
to siltstone and sandstone in
(he upper part
Gran i t ic rocks, Pre Cretaceous
schist, KHH!ss, and 1tmestnne
r;t UK i HK In HIM* f r<>m Mesov.n i c
to Pre-Camhrian
(6000) -—•> . (7000)^-
O - . • O • o . MintotHt Formitnn • - . • O .
.o.'O' -° ' »o» on'oiqp ' '(-4800)' O
fell-sorted fine to medium sand
Youngest fluvial and deltaic
de/pos I ts
Coarse-grained alluvial-fan
oKi ts. and Inc lude.s the
Oeotillo Confflomerate in
wt-stern Imper i a 1 Va 11 ey
Thin blankets of gravel and
sand overlying pediments cut
on the I'alm Spring and Imperial
Format ions In western Imperial
ValIcy
Fluvial and deltaic interbedded
arkosic sand, Kilt, and clay
depitsi ted by thi- ancest ra 1
Colorado R i ver
Coarse pebble and cobble
conRlomerate, pre-Terti ary
granitic and metamorphic
(ie. t r i t.us of 1 oca I der i vat i on
Two nonmarlne members of very
coarse grained sedimentary
breccia separated by a middle
member of marine arenite
Evaporite facies
Andesite lava, breccia, and
tuff overlies the lower part
o) Spli t Mounta In Format ion
EXPLANATION
CONTACT
liiiuii «MADATIONAL CONTACT
UNCONFORMITY
MAXIMUM THICKNESS (tott)
UNIT SYMiOt O.
aEOLOSIC MAI
Figure 2.12
Composite column of Salton Trough showing inferred time-stratigraphic
relations f estimated maximum thickness and lithology. (adapted from
Loeltz, et al.,1975)
-------
to be Plio-Pleistocene in age (Loeltz, et al., 1975). It con-
sists of interbedded light gray arkosic sandstones and reddish
clays of terrestrial origin and grades westward into the Cane-
brake Conglomerate. It contains Pliocene and/ or Pleistocene
vertebrate fossils west of the Salton Sea (California Department
of Water Resources, 1970).
The Canebrake Conglomerate of Dibblee (1954) is an unsorted
and poorly consolidated gray, coarse pebble and cobble conglom-
erate and fanglomerate containing pre-Tertiary granitic and
metamorphic debris of local origin. It is up to 2,700 m (9,000
ft) thick and of continental origin. It occurs in western
Imperial Valley and grades basinward into the Palm Springs and
Imperial Formations.
Dibblee's (1954) Ocotillo Conglomerate, probably of upper
Pliocene or lower Pleistocene age, has unconformable contacts
both in the northeast and northwest Imperial Valley. In the
northeast it overlies the Borrego Formation with a local uncon-
formity. In the northwest the San Andreas Fault lies between it
and the underlying Palm Springs Formation (Dibblee, 1954). It
is up to 760 m (2,500 ft) thick, consisting of gray, poorly
consolidated boulder conglomerate, composed mainly of granitic
and Orocopia Schist detritus, grading basinward into pink sand-
stone and claystone. It is generally distributed in forebay
areas along the Indio and Mecca Hills; to the east it grades
into the Brawley Formation.
The upper Pliocene Brawley Formation of Dibblee (1954) is
about 600 m (2,000 ft) thick. It is composed of light gray
lacustrine claystone, siltstones, minor buff sandstones, and
pebbly gravel deposits (Dibblee, 1954; California Department of
Water Resources, 1970). The Brawley Formation is lithologically
very similar to the underlying Borrego Formation ,and they cannot
be distinguished from each other where they are not in uncon-
formable contact (Loeltz, et al.,1975).
All of the remaining units lie unconformably over the older
formations previously described. They all are Quaternary to
Recent deposits and have a total thickness up to 90 m (300 ft)
(California Department of Water Resources, 1970). These units
are terrace deposits, older alluvium, lake deposits, windblown
sand and the Niland Obsidian. The first two are contempora-
neous and apparently predate the following four (Loeltz, et al.,
1975). The terrace deposits occur to the southwest of the
Salton Sea and are a "thin pediment gravel and sand, formed
mostly on the Palm Springs Formation. It may grade into fans of
older alluvium" (Loeltz, et al., 1975).
The older alluvium has major outcrops on the piedmont
slopes of the Chocolate Mountains, although it may be only a
53
-------
The Split Mountain Formation, approximately 800 m (2,700
ft) thick, has been defined by Tarbet and Holman (1944) and
redefined by Woodard (1961). It is composed of two very
coarse-grained nonmarine sedimentary breccia members separated
by a middle marine arenite member (Loeltz, et al., 1975). The
middle member includes the bedded white playa deposit of gypsum
and anhydrite up to 30 m (100 ft) thick (Dibblee, 1954). In
contrast, the California Department of Water Resources (1970)
identifies the upper member as marine and the lower and middle
members as nonmarine. However, they do not cite descriptive or
stratigraphic references in their bibliography.
The Imperial Formation is estimated to be early Miocene to
early Pleistocene, although the exact age still remains contro-
versial (Loeltz, et al. ,1975). It is up to 1,200 m (4,000 ft)
thick, of shallow marine origin, and represents the last marine
invasion of Imperial Valley. It is a light grey claystone and
lesser interbedded arkosic sandstone with calcareous oyster
"shell reefs." For a more detailed description, see Christensen
(1957), who describes a complete section in the Coyote Mountains
type area.
The Mecca Formation, up to 300 m (1,000 ft) thick, (located
off the geologic map) is exposed in the Mecca Hills in north-
eastern Coachella Valley. It is a reddish arkosic claystone
conglomerate with the basal strata containing chiefly metamor-
phic debris (Sylvester and Smith, 1976). It is of continental
origin , lies upon the basement complex and is overlain by the
Palm Springs Formation (Dibblee, 1954). It would be difficult
to accurately depict this formation in its proper place on Fig.
2.12, "Composite Column of the Salton Trough," so it has, there-
fore, been omitted.
The Borrego Formation has been defined by Tarbet and Holman
(1944) and Babcock (1974). It is up to 1,800 m (6,000 ft) thick
and grades laterally into the Palm Springs Formation. Arnal
(1961, p. 473) reported a late Pliocene to early Pleistocene age,
while Babcock (1974, p. 323) reports a Pleistocene age for this
formation. It is a light gray claystone with minor amounts of
buff lacustrine sandstone containing lacustrine fauna of minute
mollusks, ostracods and rare foraminifera. Mineralogical ana-
lyses of the Borrego Formation in the Durmid area indicate much
detritus of local origin (Muffler and Doe, 1968) while the
Borrego Formation occurring in the rest of the Salton Trough is
of Colorado River origin (Merriam and Bandy, 1965). Subsidence
of the Salton Trough at approximately the same rate as deposi-
tion of the Borrego Formation is suggested by the presence along
strike for more than 1,800 m (6,000 ft) of uniformly thin evap-
orate layers interbedded with clay and silt (Babcock, 1974).
The Palm Springs Formation of Woodring (1932) attains a
maximum thickness of about 2,100 m (7,000 ft) and is considered
52
-------
M6°W
340N
33°N -
EXPLANATION
Solton Seo Drainage-basin boundary
• uNlTEDJT
CALIFORNIA -^—MEXIC
A'CAUFORNIA \
Figure 2.13 Salton Sea drainage basin,
1976)
(McDonald and Loeltz,
55
-------
thin veneer here, and minor outcrops in Borrego Valley and
western Imperial Valley. It consists largely of coarse-grained
alluvial fan deposits and includes the Ocotillo conglomerate, in
western Imperial Valley, as defined by Loeltz, et al (1975). It
grades into the Brawley Formation towards the center of the
valley.
The lake deposits consist of sand and clay and include the
deposits of Lake Cahuilla, exposed in the middle of the trough,
and the deposits of the Brawley Formation, from which they
cannot be differentiated in the subsurface (Loeltz, et al.,
1975).
The unit designated "alluvium" occurs largely on East Mesa,
between the Sand Hills and Chocolate Mountains piedmont slope
and northward, and on West Mesa, Lower Borrego Valley, and the
southwestern Imperial Valley. It consists of the youngest
fluvial and deltaic sand, gravel and silt and some dune sand,
where the sand is less than 3 m (10 ft) thick (Loeltz, et al.,
1975).
The windblown sand unit is restricted to the Sand Hills,
although well-sorted fine to medium windblown sand is extensive
on the sides of the valley (Loeltz, et al.,1975).
The Niland Obsidian occurs near the southeast shore of the
Salton Sea, as small dome-shaped outcrops of obsidian, scoria
and pumice, and is associated with hot springs.
2 - 4 HYDROLOGY
The hydrology of Imperial Valley is described in this
section, with particular emphasis on ground water. An overview
of surface water flow and quality in the internally drained
Salton Sea drainage basin (Fig. 2.13) is presented. Water-
bearing units and their physical properties, recoverable water
in storage, ground water flow, recharge and discharge, origin of
ground water and a ground water model of a geothermal system are
discussed. The section concludes with a brief discussion of the
hydrologic budget of Imperial Valley, including inflow and
outflow of the Salton Sea drainage basin.
2.4.1 Surface Water
The Imperial Valley lies within the Salton Sea drainage
basin (Fig. 2.13). All streams in the basin flow from the
surrounding mountains, internally, towards the Salton Sea, and
all water leaving the basin is discharged through evaporation or
evapotranspiration. The Salton Sea drainage basin includes
21,640 sq km (8,360 sq mi) of drainage area (Fig. 2.13) with
about 3,600 m (11,700 ft) of relief. In the San Bernardino
54
-------
increases. However, when flow reaches permeable alluvium in the
valley, more runoff is absorbed than in the impermeable moun-
tainous areas. This results in either a change in the rate of
increase of flow, or conversely, a decrease in average flow as
the drainage area increases. Therefore, the residual flow in
channels, below the point where absorption of flow begins, does
not represent the total runoff.
Under natural conditions the soils in irrigated areas
should contribute some runoff. However, the preparation of
fields for irrigation by flooding prevents any local runoff and
therefore the contribution to runoff from irrigated areas is
negligible.
Inflow and outflow in the Salton Sea drainage basin is
discussed in Section 2.4.3,"Hydrologic Budget."
Surface Water Quality—
Salinity of surface water in the Salton Sea drainage basin
has ranged from less than 500 ppm TDS in the Colorado River at
Yuma to over 213,000 ppm TDS in the Salton Sea in 1936. Cur-
rently, Colorado River water contains 700 to 800 ppm TDS around
Yuma and 30,000 to 35,000 ppm TDS in the Salton Sea. The chemi-
cal characteristics of surface water in the Salton Sea, in its
major inflow sources and tributaries and in the lower Colorado
River are discussed below.
Salton Sea—The Salton Sea contains over 740,000 ha-m (6
million acre-ft) of sodium chloride water. In June 1967 it
contained an average TDS of about 36,000 ppm, which is slightly
more saline than ocean water.
The composition of the water varies with time and with
location in the sea. Changes with time are due to variations in
sea volume, mineral content of inflowing waters and precipi-
tation of ions from the water when concentrations reach solubil-
ity limits. This temporal variation is shown on Table 2.2.
Changes of composition with location and depth are due to slight
circulation of Salton Sea water, to locations of inflow channels
and to surface evaporation.
The first chemical analysis of the Salton Sea, in June
1907, reported the mineral content of the sea as approximately
85 million metric tons (77 million tons) and 3,600 ppm TDS. The
salinity of the sea rose from 3,600 ppm in 1907 to 40,000 ppm in
1925, mainly due to the continued solution of minerals from the
sea bed and the rapid decline in sea volume by evaporation. As
the quantity of soluble minerals on the sea floor decreased, the
rate of increase in mineral content gradually slowed. The
highest salinity was measured in 1936, as 213,000 ppm, after a
shortage of irrigation water in 1931-35.
57
-------
Mountains, along the west and northeast rims of the basin,
elevations range from less than 900 m (3,000 ft) to more than
3,500 m (11,500 ft). About one fifth of the area of the basin
is below or just slightly above mean sea level (msl). The
surface drainage pattern is indicated by the flow direction
arrows on Figure 2.13.
Historically, the Colorado River has discharged water and
sediment via the many distributaries in its delta, and in the
past, some of these distributaries have flowed northward into
the Salton Sea basin. Currently, the Colorado River flows
southward to the Gulf of California; thus,the natural drainage
area of the Salton Sea is now topographically distinct from the
delta region of the Colorado River. This separation was aug-
mented early in this century by construction of levees on the
delta to prevent overflow to the north. Permanent separation of
the two drainage basins was ensured by later construction of
numerous flood-control reservoirs in the Colorado River basin.
The Salton Sink, the lowest area in the Salton Trough, is
currently occupied by the Salton Sea. The sink also contained
water during at least eight years of the nineteenth century
(MacDougal, 1914), and in the past few centuries it has occa-
sionally contained water as a result of unusual runoff from the
bordering mountains or overflow from the Colorado River.
Irrigation began in Imperial Valley in 1901. Additional
diversion channels for irrigation and flood protection were
constructed after 1901, but before they could be properly pro-
tected a series of floods eroded them. This flooding diverted
nearly the entire flow of the Colorado River into the Salton Sea
basin. Flood water began to collect in the sea in November
1904 and continued until February 1907. The depth of the
Salton Sea was more than 25 m (80 ft) and it covered over 1,300
sq km (500 sq mi) by 1907. The water level receded 17 m (55 ft)
in the next 12 years. However, increasing drainage from irri-
gation reversed this trend around 1925. in 1970 the elevation
of the Salton Sea shore was -71 m (-234 ft) and the maximum
depth was about 12 m (40 ft).
Runoff—
The Imperial Valley depends mostly on irrigation canals and
deep wells for its water, although runoff from the surrounding
mountains contributes some water to perennial streams. Runoff
in arid regions is dependent on drainage by ephemeral streams
which flow only briefly during and after some storms. The water
table is far below most of the local stream channels, which
often traverse deposits of alluvium. These deposits absorb a
part or all of the flow that originates in relatively imperme-
able areas in the mountains surrounding Imperial Valley, where
there are no extensive alluvial deposits. The average flow in a
channel of this type tends to increase as the drainage area
56
-------
TABLE 2.2
CHEMICAL ANALYSES OF WATER FROM THE SALTON SEA
(Hely, et al., 1966)
[Concentrations in parts per million]
Apency '-
Ciilcium
l.Ca)
Sodium Ulcarlxm-
and pot.is- | ale
slum I (IICUj)
(Na+K) |
SuUule
(SO.)
Chloride
(CI)
Salinity
(culculatc'ijj-
Volunio fjf
W.ltIT
(millii,: s of
cicre-fl;
June 3, 1907 CI
Nov. 12,1907 ! csus
Fel>. 28, 1908 ; I'SGS
MaviS, IRIS j CI
Julie!-, 1909 : CI-
May:;, Kun ci
JuiieS, 1911 CI.
June 10, I'Jl.' CI
Junel>. 1013 | CI
June 12. Kit ! CI
Junes. 1915 ' 01..
June 10. I'Jl''.-- ' CI -
Ju:ie 10, 1923 CI..
M:ir 21. I9-*! C il .
Dec. 2-2. 1945 | III)
1
Dee.20, 194fl i III)
Dec. 17, l'.)47 Ill)
Sept. 20. IMS III).
Dre. 15. 1946 1II>_
Sept. 1'J. 1949 1 III)
Dec. IS. 1949 IID
Sept. 20. 19511.--- i III)
Dec. 20, 1950 ! Ill) i
May 19. 19f.| ' III).---, i
Sept. 25, 1951 IID .j
June 4. 1952 IID
Nov. 19, 19,'.2 ..- Ill) j
May IS. 1953 Ill) |
Nov. 23. 1953 ! III)
Mjy 24, 19.54 i IIU j
Nov. IS. 1954 IID
June 13, 1955 IID - -, '
Nov. 21. 1955 - IID |
May 21. 195i> IID
Dec. 10, 1950 IID '
May 27.1957 IID
Nov. 25, 19"i7 IID
May 12. 1958 III) .
Nov. 10. 1958 IID
May 25, 1959 IID _|
Nov. 9, 1959 IID
May27,l%0 IID _. . _,
Nov. 11, 19liO Ill)
Apr. 4, 19B1 I'SGS I
May 22, 191)1 IID |
Sept. 22. ]9B1.___ TSGS '
Nov. 20. 19fil I IID |
Jan.2!>. 19i52 ... I USf.S
Mar. 19. 1902 ! USGS j
; i
May 21. 19(52 IID I
S"pt. 10, 1902.... I USGS
Nov. 12. 1902 III)
May 8, 1903 USGS -
Oct. 10, 19M rsc.s
Nov. 4, 19(13 ... Ill)
M:iy 18, 1904 IID
May 28. 1904 VSGS
100
107
142
ll'i !
173 i
190
253
1*4
7(i'5
780
8119 !
918
782 •
850 I
830 i
SIS
SI2
808 i
9(14 i
912 i
872
742
721
70S
756
738
774
759
840 |
807 ,
813 i
821
813 '
I
850
811 I
831 '
79(5
801
R02
702
K20
90.5
98
117
13i5 !
1(12 I
190
800 •
921 i
942 j
1.050 j
9915 i
1.0 JO i
953 j
1,1211 ;
9i,3
990
985
909
93'J
899
891
878
930
889
889
905
910
94il
939
951
9.50 !
9 '9 :
1, 020
9H1
905
937
9x5
1.010
928
904
908
1.010
928
1.140
1.2C.O
1,200
1.370
1,1120
4. 430
,'i. 331)
12,5UU
"ll.lOO |
11,000
11.100 '
12,100 •
11.300 i
11. MB
11,200 !
11,71111
11.21111 -
in,800 '
12.100 j
10.400 I
10. (500 !
10.200 !
10. oiw '
9,830 ;
9.940
9.1520
10.000 '•
9.980 ;
10,200
9.9*0
10.200
10.100
10.300
10.100
10.800
10,400
10. 4CO
9,830
10. 100 !
10. 100 |
10.100 I
10.000 |
9.910 j
10.100
10.100
10.100
9,590
9,740
9.3-0
9.700
9.540
134 i
1(55 :
12U I
117 I
I1
242
232
Hj'J '
207
210
HIS
213
217 '
202
221 I
204 •
209 ,
|
213 '
192
212
212
215
208
204
204
200
200 i
200 j
109 I
179
208
204
191
199 !
182 j
197
174
183
174
19(1
177
192
107
17S
198
175
180
917
1,070
1.250
1,4011
1,740
2, IIM!
.". 3M1
0.900
(i. 990
7.490
7. 150 ]
7. 580
7,1(50 '
7. 350 j
7. 1211 I
II. 950 j
7,210
(i. 520 .
0.810
(1.830
7, I'lO
I
7. 050 i
7,300 I
7. 170 '
7.330 I
7.100 i
7 3'50 I
7.130 1
7.290 i
7.0150 ;
7.230
7.260 ;
7. 21.0
7.250
7.140
7.250
7.320 '•
7,2i>o;
6,900
7.210!
6.900 '
7. 110 :
7.010 :
1.700
1,8311
l.V'JH
2. (140
2.41U '
I
2. am !
15.9HO !
17! 41*1 !
HI. vii) i
17.201)
IS. 4(10 •
17.100 ;
1(1.200 i
1 i. BOO
17,000
14.900
1 ">, 200
14. UK)
14.7DII
14,400 j
14.300 !
13,900
14. .'00 i
14.100 !
14 300 I
14.100 '
14.300
14.300
14. 500
14.300
15.200
14.1,00 I
14.SOO
14.000
14.400 |
14.000
14.400
14.200
14, 100
14.300
14. 400
14.400
13. (500 i
13.SOO :
14.400 ,
13.900
13. 500
3.550
3.9111
4.II7II
4. 251)
4.'.'Ml
35. 700
35.9110
38.91111 '
3'5. »W
3V2IK1
3li. 41*1
35.5110
38.800 |
34,000
34, 000
33,400 .
33, 400
32. liuo
32. ran
31.800
32. 700
32, (.015
33,400
I
32.900 j
33.1,00
33.400
33.900 i
33.300 |
35.200
3:i. COO
34. 400
32. 700
3.1. iiOO
31.000
3:>. 70')
33. 300
33.000
33. r,00 !
33. 700 !
33,700 !
32.001!
32.1500 '
31.HOO ]
33.000 I
31.800
15
I.I
14
13
4 05
4 01
3. '.(4
3.97
4 IJJ
4.0-
4 11
4. 20
4 4"
4.31 ,
4. 72
4. '17
4.94
4.92
5.21
5.23
5.40
5.40 '
- 110 '
77
80
83
01
2i)4
214
JH
221
224
223
232
22S
229
240
239
241
239
247
241
245
2151
•5K
259
J5S
1 Agencies responsible for publication or flic data: CI, Carm-pie Institution of Washington; Cul, state of California; III1, I
t'.S. Geolopica] Survey. Data were obtained from the following publications or files:
! Irrigation Dijtrict; I Si',-:
Years
1907-111 CI .
1907-OS VSGS.
1923 CI
1929 Cal.
Symbol
Source
Svkes (19371.
Van Winkle and Eaton (1910).
Carneeie Institution or Washington (1924).
Cnh'inaii (19291.
1945-(54 .- IID Files of the Imperial Irrigation District.
]9(il-04 USGS Filesof the U.S. Geological Survey.
2 Calculated as the sum of constituent? shown using half Ihe bicarbonate concentration, except that for 1929, which was dcterminc'l by evaporation.
59
-------
The Salton Sink, as a topographic low, has been subjected
to inundation, sedimentation and subsequent evaporative cycles
over many thousands of years. When the waters evaporated, large
salt deposits formed which were then covered during the next
inundation-sedimentation cycle; thus many wells in Imperial
Valley show increasing salinity with depth.
A 1927-28 study of the Colorado River at Yuma, Arizona,
reported the weighted-average concentration of dissolved solids
in the river as less than 513 ppm (Howard, 1955). Based on this
figure, the amount of minerals contributed to the Salton Sea by
the Colorado River between November 1904 and June 1907 was less
than one-seventh of the mineral content measured on June 3,
1907. Therefore the sea bed itself must have supplied the
remaining mineral content.
Sodium and chloride have been the major dissolved constitu-
ents in the Salton Sea and will remain so because of their high
solubility. Sulfate has been the next most abundant ion. The
ratio of sulfate to chloride in the sea has increased and is
still increasing (Table 2.2). Some other constituents in the
sea are calcium, magnesium and bicarbonate.
Comparison of the Salton Sea inflow with Colorado River
water indicates a large increase in the concentration of all
ions except bicarbonate (Table 2.2). Carbonate was apparently
deposited in the soils or removed by biological activity. This
increase in sodium plus potassium and in chloride (Table 2.2) is
partly accounted for by concentration due to evapotranspiration,
but a greater amount of these constitutents has probably been
leached from soils irrigated with Colorado River water.
Concentrations of calcium and sulfate are apparently at or
near levels which will form a gypsum (CaS04 2HLO) precipitate.
As the salinity of the sea increases, calcrum Snd sulfate con-
centrations will be partly controlled by the precipitation of
gypsum. When the sea becomes saturated with gypsum,a nearly
constant sulfate concentration may result.
Major Inflow Sources and Tributaries—The natural saline-
mineral content of soils in most of the Imperial and Coachella
Valleys was high before irrigation began. Some soils that were
initially too saline for agricultural production had to be
leached. The first irrigation attempts in Imperial Valley were
carried out on level farmland without provision for drainage
except through natural channels. Water logging and salt accumu-
lation soon occurred. To alleviate this problem and create a
favorable salt balance—that is, to have the quantity of dis-
solved mineral salts delivered in irrigation water be less than
the quantity removed from the area by drainage—an extensive
tile drainage network was installed throughout the irrigated
areas of Imperial Valley. Imperial Irrigation District (IID)
58
-------
TABLE 2.3 SELECTED CHEMICAL ANALYSES OF SURFACE
WATER IN THE SALTON SEA BASIN (IreIan, 1971)
[Results in milligrams per liter unless otherwise indicated]
No.
1.
2.
3.
4.
S.
6.
7
R
9
10.
Source
Alamo River at international boundary
Alamo River at international boundary . . _
Alamo River near Niland
Alamo River near Niland.
New River at international boundary .
New River at international boundary
New River near Westmoreland
New River near Westmoreland
Whitewater River near Mecca
Whitewater River near Mecca
Date
1
Feb. 5, 19fi2
May 2, 1902
Dec. 30. 1904...
Mar. 20, 1905 ..
Jan. 12, 1905 ...
June 15, 1905...
Dec. 30, 1IM1-I
Mar. 20, 19(15
Nov 17 1904
June 7, 1905
^
M
n
2.0
42
039
780
124
122
380
5 13
82
139
oo?
to
13
14
13
10
25
22
20
11
18
18
.E «?
O
199
172
250
230
284
200
238
1110
170
aenesium
(Mg)
S
108
70
100
108
<»3
1 20
123
108
It
S
.. 2
II lg
S £
on
380
72(1
550
1 , 330
1 , 1 20
827
1100
530
carbonate
(HC03)
«
311
288
251
221
200
210
208
250
330
330
«'?
1,000
075
975
8'V>
07.5
7.)0
850
750
950
825
|^
U
090
455
1,100
833
2,500
2.190
1 , 750
1,310
472
435
K o n
o
2,490
1,910
3,410
2 . 070
5.350
4,800
4 , 250
3 , 380
2,420
2,190
aecifio
conductance
(micromhos
at 25°C)
to
4,150
3,200
5,530
4,180
9,000
7,940
7,010
5,430
3 , 070
3,410
-------
sample analyses indicate that mineral salts accumulated in the
valley through 1948, but since then the quantities of dissolved
mineral salts leaving the valley in drain water are greater than
the quantities entering canal waters.
Selected chemical analyses of surface water in the Salton
Sea basin are presented in Table 2.3 and are discussed below.
The salinity of the Alamo and New Rivers (Fig. 2.13) flow-
ing into the Salton Sea varies according to the proportions of
canal water and drainage water in each. Usually the New River
is considerably more saline than the Alamo River. A small flow
source to the Alamo River and a much larger source to the New
River is drain water from the Mexicali Valley. Irelan (1971)
reports that more frequent drain samples are necessary before a
mineral budget for Imperial Valley can be established.
The Alamo River, sampled near Calipatria in 1967, has an
annual flow of 62,000 ha-m (500,000 acre-ft). TDS content is
about 2,500 ppm. The water has a sodium chloride sulfate char-
acter and a fluoride concentration of about 1 ppm.
The New River near Westmorland has a sodium chloride char-
acter with almost 1 ppm fluoride concentration and a TDS of
around 3,500 ppm. Its annual flow is less than 62,000 ha-m
(500,000 acre-ft).
The Coachella Valley, unlike Imperial Valley, is underlain
by productive aquifers of fairly low salinity. Colorado River
water has replaced much of the ground water previously pumped
for irrigation. Based on rough computations for 1962-65, it
appears that more chloride left the valley than entered it
through canal water and that sulfate concentrations entering and
leaving were nearly equal.
At Mecca (Fig. 2.13), the Whitewater River, flowing an-
nually at less than 12,300 ha-m (100,000 acre-ft), has a TDS of
about 2,000 to 2,500 ppm. The water shows a fairly high fluo-
ride concentration of 3.5 ppm and has a sodium sulfate chloride
nature.
San Felipe Creek (Fig. 2.13) runoff is mostly flood water
and varies from 12 to 1,100 ha-m (100 to 8,700 acre-ft) per
year. Chemical analysis from 1955 to 1957 showed a range of
7,000 to 9,000 ppm TDS, a sodium chloride character and notable
sulfate concentrations.
Salt Creek (Fig. 2.13), measured in 1967, was sodium chlo-
ride in character, showed a high fluoride concentration and
contained about 4,500 ppm TDS. It has a constant flow derived
mostly from Coachella Canal seepage of approximately 490 ha-m
(4,000 acre-ft) per year.
60
-------
so that sediments of the southern and eastern Imperial Valley
are much coarser than northern and central valley deposits
This relationship generally holds to a depth of at least 2,000 m
(6,600 ft) (Randall, 1971) and holds best for central and east-
ern valley deposits. West valley deposits are less affected by
contributions from the Colorado River than by deposition from
local sources. Other processes tend to concentrate coarse
deposits (sands) on the flanks and fine deposits (clays) in the
central valley. The action of northwest prevailing winds con-
centrates sands in southern and easterly dune belts; deposition
in the several post-Miocene lakes has concentrated clays and
evaporites in the central Imperial Valley. The net effects of
these sedimentary processes are: 1) they tend to form natural
stratigraphic cap rocks for central valley geothermal systems,
2) they separate shallow and deep ground water systems, and 3)
they make central valley waters saltier and more stagnant than
eastern or western waters.
All of the deposits of hydrologic interest are deltaic,
lacustrine, fluvial or alluvial sediments of nonmarine origin.
The most recent nonmarine unit is the Imperial Formation which
lies deeper than 4,097 m (13,443 ft) in the central Imperial
Valley (Muffler and Doe, 1968). The sedimentary sequence thick-
ens towards the center of the valley, and individual beds and
layers are difficult to trace or delineate due to the nonuni-
form, lensing nature of the deposits. The valley is crossed by
numerous known, inferred and yet to be located faults, most
trending northwest-southeast (Plate 2.2). These faults act as
ground water barriers and conduits introducing local alterations
in water table levels and flow patterns. Meidav and Furgerson
(1972) have shown that many faults of the San Andreas System act
as aquitards for valley waters. They postulate that high salin-
ity gradients existing across northwest trending faults further
increase salinities of central valley ground water by forming
barriers to fluid mixing. It was noted, for instance, that
artesian waters exist only east of the Alamo River, suggesting
that this river marks one of the proposed aquitards. Meidav and
Furgerson (1972) have also observed salinity increasing from the
southeast to the northwest. This could be accounted for by
assuming a single recharge source at the Colorado River. Waters
northward and westward would be further along the flow path from
the Colorado River towards the Salton Sea, implying that these
waters could become more saline due to longer contact with
reservoir rocks.
The regional water flow pattern is complicated, but in
general ground water flows northward and westward towards the
Salton Sea as underflow from the Colorado River. This regional
flow is generally separated into a shallower and a deeper hydro-
logic unit. Ground water in both units flows in the same direc-
tion, but faults and lithologic discontinuities complicate the
basic pattern. These geologic features may channel or obstruct
63
-------
Lower Colorado River—Approximately 740,000 ha-m (6 million
acre-ft) of Colorado River water flows annually to Imperial Dam.
The major portion is allocated to the Ail-American Canal, a
lesser amount to the Gila Gravity Main Canal, and the remainder
is released down the river channel.
All the irrigation water for Imperial Valley is derived
from the All-American Canal. The Colorado River water entering
the canal at Imperial Dam has contained from 637 to 912 mg/1 IDS
during the 25-year period from 1941 through 1965 (Irelan, 1971,
p. E-12). There have been fluctuations in the general trendxbut
the mineral content of this water has generally increased from
less than 800 mg/1 through 1954 to a 800 to 900 mg/1 range
during 1955-65. This increase in salinity is due to increased
irrigation and water diversion above the dam.
In Cibola Valley, above Imperial Dam (Fig. 2.13), much
irrigated acreage has been added in the last two decades but no
surface drains have been constructed. Leaching of soluble salts
from this land has added substantially to the Colorado River's
mineral burden at Imperial Dam. Irelan (1971) reports that Palo
Verde and Parker Valleys (Fig. 2.13) exchange some sodium in the
soils for calcium. Common salt (sodium chloride) is also leached
from these valley soils. The combined water budgets for the
Colorado River between Parker and Imperial Dams (1961-65 data)
indicated deposition of calcite and gypsum, some base-exchange
replacement of calcium by sodium and removal of sodium
chloride.
The ever-increasing diversion of water to the Colorado
River Aqueduct has resulted in an increase in ionic concentra-
tion at Imperial Dam. The amount of water available for dilut-
ing the more concentrated inflows is reduced by the quantity of
water diverted from the river.
2.4.2 Groundwater
Local geology plays an important role in determining ground-
water quality and distribution in Imperial Valley. The hydro-
logic and chemical characteristics of Imperial Valley waters are
highly dependent on sedimentary stratigraphy and the waters'
location with respect to prominent faults. Hydrothermal pro-
cesses may also play an important role in altering water quality
and flow characteristics.
Sedimentary deposits are heterogenous and range from imper-
meable clays to very permeable coarse sands and gravels. The
areal and vertical distribution of sediments in the valley are
strongly related to contributions from the Colorado River, which
has been the dominant source of valley sediments since the
Miocene (Muffler and Doe, 1968). In general, the grain size of
valley sediments is inversely proportional to the distance from
the present-day Colorado River Delta (Merriam and Bandy, 1965)/
62
-------
Dutcher, et al., (1972) present a general conceptual hydro-
logic model on which they based estimates of ground water in
storage. They divide the ground water regime into four depth
zones from the surface to the basement complex and further
subdivide the nearest surface zone into four ground water stor-
age units. They then estimate the quantity of recoverable water
in each unit based on estimates of porosity, specific yield,
thickness and areal extent of each unit.
The data presented in Dutcher, et al. (1972) is based on an
insufficient amount of control data and an unproven conceptual
model. Estimates are based on huge extrapolations of meager
data and even though they may be the best estimates attainable
with available data, they may be subject to extreme modifica-
tions. Therefore these limitations should be recognized in the
following discussions which refer to the work of Dutcher, et al.,(1972)
Loeltz, et al.,(1975) address only the upper few hundred
meters of heterpgenous nonmarine deposits. They include trans-
missivities derived from pump tests, specific yield derived frpm
soil moisture studies, ground water movement, discussions of
recharge and discharge and ground water quality. Although this
was published in 1975, the study and report was completed by
1966 (Olmsted, pers. comm., 1977) and therefore does not include
any information collected since 1966.
Hardt and French (1976) is strictly a data compilation of
over 430 wells in Imperial Valley. It includes complete water
quality and sample depth interval data for 74 wells. These data
were used extensively in the water quality section in prepara-
tion of modified Stiff and Langelier-Ludwig diagrams and in
contouring of water parameters. Reed (1975) and Cosner (1977)
provided additional water quality data for the artesian aquifer
and geothermal wells, respectively.
Limitations of Data—
We have made no attempt at original data generation in this
phase of the study and have utilized data available from pre-
vious studies, assuming it to be correct unless discrepancies
became apparent. This is particularly relevant with respect to
the water quality data. It was beyond the scope of this report
to reconcile differing sample procedures and analytic techniques
used by different workers. The available data were compiled,
interpreted and described using standard hydrologic and geo-
chemical techniques. If the results seemed reasonable, the raw
data was considered sufficient.
It is important to note again the great extrapolations used
by Dutcher, et al., (1972). Their conclusions are based on
conceptual modeling of the mechanism and elements of the hydro-
thermal system. The accuracy of their estimates is only propor-
tional to the reliability of their conceptual model and their
raw data, collected up to June 1971.
65
-------
water flow, and local convection patterns from hydrothermal
systems may cause regional waters to flow towards geothermal
anomalies. Separation of deep and shallow aquifers also tends
to complicate flow patterns, especially when shallow and deep
waters can communicate by fault-induced permeability. In some
cases careful analyses have allowed local flow patterns to be
deduced (Bird, 1975).
The major ground water flow, in addition to underflow from
the Colorado River, comes from canal leakage and irrigation
discharge. The original source of all of this water is the
Colorado River. These Colorado River waters flow towards the
central and northern portions of the valley and finally into the
Salton Sea. Minor contributions to the ground water system come
from northward underflow from the Mexicali Valley and local
runoff flowing towards the center of the valley from the moun-
tains on the eastern and western margins. Ground water flow in
aquifers deeper than 900 m (3,000 ft) is probably downward from
the shallower aquifers and then radially towards heat anomaly
convection cells (Butcher, et al.,1972). Once in the convection
cells, the water recirculates as convection currents.
The flow rate of Imperial Valley wells is variable and
depends on the location and depth of the well. Many shallow
wells at eastern and western valley margins have flows greater
than 3,800 1pm (1,000 gpm), whereas central valley shallow wells
have produced only a fraction of this. This is partly why the
extensive irrigation system was needed in Imperial Valley. Deep
wells in the central valley, however, flow as well or better
than deep wells at the valley margins. Adequate sampling of
these wells is not yet available to establish a clear pattern.
The total volume of water in storage has been estimated
between 2.0 and 5.9 x 108 ha-m (1.6 and 4.8 billion acre-ft)
depending on the porosity depth function used (Rex, 1970, p.
14). Combs (1971, p. 11) estimated a total of 2.6 x 108 ha-m
(2.1 billion acre-ft) total water in storage between 900 and
3,000 m (3,000 and 10,000 ft) depth. Dutcher, et al., (1972)
estimated 2.0 x 108 ha-m (1.6 billion acre-ft) of water with
less than 35,000 mg/1 TDS in Imperial Valley.
Previous Investigations—
Three major sources for hydrology and ground water quality
data in Imperial Valley are "Preliminary Appraisal of Ground
water in Storage with Reference to Geothermal Resources in the
Imperial Valley Area, California" (Dutcher, et al., 1972);
"Geohydrologic Reconnaissance of the Imperial Valley, Cali-
fornia (Loeltz, et al.,1975); and "Selected Data on Water
Wells, Geothermal Wells and Oil Tests in the Imperial Valley,
California (Hardt and French, 1976). These references were
used extensively and many other site-specific sources were
utilized for additional detail.
64
-------
EXPLANATION
Ground-water basin boundary
Fault'
Dashed where approximately located;
dotted where concealed; queried
where doubtful.
_ — 6 — ——
Line of equal thickness of deposits
with water containing less than
35,000 mg/| IDS. in the basin,
in thousands of feet.
Interval 1,000 feet.
10
20 (Ml)
10 20 SO (*«)
Figure 2.14 Total thickness of deposits with water containing less than
35,000 mg/1 dissolved solids. (Dutcher, et al.,1972)
-------
Water-Bearing Units—
Hydrologic investigations of Imperial Valley have generally
referred to about a thousand meters of upper water-bearing strata
and a confined aquifer below separated by a relatively imperme-
able clay layer (e.g., Loeltz, et al., 1975; Geonomics, 1976).
To date, no one has attempted to correlate aquifers with indivi-
dual geologic formations (described above in Section 2.3.4,
"Stratigraphy and Lithology of Salton Trough Rocks"). Due to
"intermittent and interfingering alluvial fan, flood-plain and
lacustrine" sedimentation (Sylvester and Smith, 1976) and active
tectonics of Imperial Valley, it is impossible to project the
spatial distribution of these units over any considerable area.
Sylvester and Smith (1976) further note "stratigraphic thickness,
age relations, and correlation of various lithologic units along
strike and across faults are tenuous because of numerous diastems,
abrupt facies changes, the lack of fossils, and distinctive
marker beds."
Dutcher, et al.,(1972) have taken the upper-lower classifi-
cation further by dividing the lower and deeper water-bearing
strata into three essentially horizontal units, one on top of
another, and by dividing the upper water-bearing strata into
four areal hydrologic units. Their objective in establishing
this classification was to enable estimation of the total quan-
tity of usable and recoverable water in storage in Imperial
Valley. These classifications are based on each unit having
similar estimated porosity and/or specific yield. They define
the thickness and areal extent of each unit in Figures 2.14, 2.15,
2.16, 2.17 and 2.18. All of the units have "their thickest
sections in the center of the valley parallel to the north-
northwest axis of the valley. The total thickness of deposits
with usable water attains a maximum of 4,600 m (15,000 ft) in
the south central valley (Fig. 2.14). These units can be con-
sidered aquifers, originally defined by Meinzer (1923) as any
water-bearing formation; however, they should be considered only
in a general classification sense, not as continuous units with
distinct confining boundary layers.
Hydrologic section A-A1 (Fig. 2.19) crosses the valley
along its axis,and hydrologic sections B-B' and C-C' (Figs. 2.20
and 2.21) cross the valley perpendicular to the valley axis.
These show schematic cross sections of the hydrologic units,
including their respective specific yields, isothermal contours,
areas of ground water with more than 35,000 mg/1 TDS, a sketch
of the configuration of the basement-complex surface, locations
of selected data wells and fault locations. The four depth
zones depicted in these hydrologic sections, and mentioned
previously, are described below as defined by Dutcher, et al.
(1972).
Zone 4 is the deepest zone and is defined as containing all
reservoir rocks with recoverable water containing less than
66
-------
ZONE-3 Temperature more than IOO°C
Depth less than 8,000 feet .
Formation porosity 20 percent
Recoverable water 16 percent
(<35,000 mg/J IDS)
EXPLANATION
Ground- water basin boundary
Fault
Dashed where approximately located;
dotted where concealed ; queried
where doubtful
Line of equal thickness of deposits
with water containing less than
35,000 mq/f JDS in zone 3
in thousands of feet. Queried
where doubtful. Interval 1,000ft.
10
10
20 (ml)
20 30 (km)
Figure 2.16 Total thickness of deposits with water containing less than
35,000 mg/1 dissolved solids in zone 3. (Dutcher, et al., 1972)
-------
ZONE-4 Temperoture more than 100°C
Depth more than 8,000 feet
Formation porosity 5 percent
Recoverable wate' 5 percent
(< 35,000 mq/i TDS)
EXPLANATION
00
Ground-water basin boundary
Fault
Dashed where approximately located;
dotted where concealed; queried
where doubtful.
Line of equal thickness of deposits
with water containing less than
35,000 mg/j? TDS in zone 4.
i n thousands of feet .
Interval 1,000 feet.
10
10
20 (ml)
20 30 (km)
Figure 2.15 Total thickness of deposits with water containing less than
35,000 mg/1 dissolved solids in zone 4. (Butcher, et al.,1972)
-------
ZONE-I Temperature. lets than IOO°C
Depth 0-3,000 feet .
Formation porosity 25 and 30 percent.
Recoverable water, 0,15 and 20 percent.
_, (< 35,000 mg/< IDS)
*P
EXPLANATION
Ground-water basin boundary
Area of ground-water storage units
Numbers are specific yield of
deposits, In percent
Line of equal thickness of deposits
with water containing less than
35,000 mg/f TDS in zone I.
in thousands of feet.
Interval 1,000 feet.
o
r-
0
10
20 (ml)
10 20 30 (km)
Figure 2.18 . Total thickness of deposits with water containing less than
35,000 mg/1 dissolved solids in zone 1. (Dutcher, et al.,1972)
-------
ZONE-2 Temperature less than IOO°C
Depth more than 3,000 feet, less than 8,000ft
Formation porosity 20 percent
Recoverable water 13 percent
(<35,000 mg/J,! TDS)
EXPLANATION
Ground-water basin boundary
. 9
Fault '
Dashed where approximately located,
dotted where concealed; queried
where doubtful.
)am'
4
Line of equal thickness of deposits
with water containing less than
35,000 mg/I TDS in zone 2.
in thousands of feet.
Interval 1,000 feet.
10
zo (mi)
I
B»i* 1 re" _ .
Cllilolnii iiinlh h»l I ) 1.500 000 I9TO
10
20 30 (km)
Figure 2.17 Total thickness of deposits with water containing less than
35,000 mg/1 dissolved solids in zone 2. (Dutcher, et al., 1972)
-------
B
u>
2000'
SEA LEVEL-
2000'
4000
ZOftOO
u
s
_J
3
I
<
s
B'
EXPLANATION
2000'
fc
?
'#«r x
w&es*' .,*v:
WJ ^^^
v^rr*-"
ESff^aJTT ,h
F%thHf
i.
-h SEA LEVEL
5^- 1\ -^-2000'
f'60^V'J \D 28MT
-3 \ >« .^--4000'
VERTICAL EXAGGERATION ZQ.633 =
- \ 8,000
eqpoo'
FAULT
QUERIED WHERE DOUBTFUL
1
TD 4729
OS 260,000
SELECTED WELL FOR SECTION.
TD TOTAL WELL DEPTH IN FEET.
DS DISSOLVED SOLIDS IN WATER,
IN MILLIGRAMS PER LITER.
50° — ? —
LINE OF EQUAL TEMPERATURE
QUERIED WHERE UNKNOWN.
INTERVAL 50° CELSIUS
LINE SHOWING BASE OF WATER
CONTAINING LESS THAN 35,000 MILLI-
GRAMS PER LITER DISSOLVED SOLIDS
VERTICAL DEPTH -ZONES
NUMBERS ARE SPECIFIC YIELD OF
DEPOSITS , IN PERCENT
In, I I
1)
n
WATER WITH MORE THAN 35,000 MILLI-
GRAMS PER LITER DISOLVED SOLIDS
Figure 2.20 Hydrologic section B-B'. (Dutcher,
BASEMENT COMPLEX
et al.,1972)
-------
EXPLANATION
(Well 85
Colipatrla Fault
Well 82
FAULT
QUERIED WHERE DOUBTFUL
1
TO 8
OS 13,000
SELECTED WELL FOR SECTION.
TD TOTAL WELL DEPTH IN FEET.
DS DISSOLVED SOLIDS IN WATER,
IN MILLIGRAMS PER LITER.
50°
LINE OF EQUAL TEMPERATURE
INTERVAL 50° CELSIUS
LINE SHOWING BASE OF WATER
CONTAINING LESS THAN 35,000 MILLI-
GRAMS PER LITER DISSOLVED SOLIDS
VERTICAL DEPTH-ZONES
NUMBERS ARE SPECIFIC YIELD OF
DEPOSITS, IN PERCENT
Son Andreas Fault Zone
a
WATER WITH MORE THAN 35,000 MILLI-
GRAMS PER LITER DISOLVED SOLIDS
Figure 2.21 Hydrologic section C-C'.
BASEMENT COMPLEX
QUERIED WHERE DOUBTFUL
(Dutcher, et al.,1972)
-------
35,000 mg/1 TDS at depths greater than 2,438 m (8,000 ft). The
2,438 m (8,000 ft) boundary was chosen somewhat arbitrarily due
to decreasing porosity and permeability and increasing tempera-
ture and metamorphism below such depths. In general the rocks
below 2,438 m (8,000 ft) are fractured, have very low inter-
granular permeability and have an average estimated porosity of
about 5%. The areal extent and thickness of zone 4 deposits—
that is, the thickness of deposits between the basement-complex
contours (Rex, et al., 1971) and the 2,400 m depth plane--is
shown in Figure 2.15. The maximum thickness is about 2,100 m
(7,000 feet) south of Holtville and occurs between mapped
traces of the Imperial and Brawley Faults.
Zone 3 is areally much larger and not as thick as under-
lying zone 4. Zone 3 is defined as that volume of sediments
between the 100°C (212°F) isothermal surface and the 2,438 m
(8,000 ft) boundary of zone 4- The thickness and areal extent
of this zone are shown in Figure 2.16. It reaches a maximum
thickness of approximately 2,100 m (7,000 ft) about 32 km (20
mi) east of Holtville. It thickens to over 1,800 m (6,000 ft)
in two other areas, one centered about 11 km (7 mi) southeast of
Holtville and another centered about 10 km (6 mi) northeast of
Westmorland. Both of these areas are essentially between the
mapped traces of the Calipatria and Brawley Faults.
Zone 2 includes all deposits below 914 m (3,000 ft) to the
top of the 100°C (212°F) isothermal surface (top of zone 3);
hence all the water contained in zone 2 will have temperatures
less than 100°C (212°F). The thickness and areal extent of zone
2 is shown in Figure 2.17. it attains a maximum thickness of
about 1,200 m (4,000 ft) in three large areas. The area east of
the Calipatria Fault is over 40 km (25 mi) long and 5 to 11 km
(3 to 7 mi) wide; another area centered about 6 km (4 mi) south-
southeast of Holtville is about 13 km (8 mi) in diameter; and
the third area of zone 2 maximum thickness is irregularly
shaped, from 18 to 27 km (11 to 17 mi) wide in the southwest
portion of the valley. The porosity for this zone is estimated
to be about 20%.
Zone 1 is defined as deposits below the water table to
either 914 m (3,000 ft) depth, the bedrock surface or the 100°C
(212°F) isotherm, whichever is shallowest. It attains its
maximum thickness of 914 m (3,000 ft) over most of the central
part of the valley (Fig. 2.18). This zone is further divided
areally into four sections, called the Sand Hills area, the East
Mesa area, the Main Valley area and the West Mesa area (Fig.
2.18). These areas have specific yields assigned for the water
storage computations, of 20%, 15%, 0% and 15% respectively. The
Main Valley specific yield is considered 0% because any water
derived from the ground in this highly irrigated area would be
imported from the Colorado River through the irrigation system
and not from a naturally recharged ground water reservoir.
75
-------
Depth Classifications Used in This Study—The extent and
depth continuity of the nearer-surface ground water units are
not well-defined in the Imperial Valley area. A division of the
shallower water -bearing strata into a general framework of
geometric distribution of water flow and occurrence is necessary
to enable correlation of water quality parameters and water
chemistry changes. Correlation of geologic units is extremely
difficult in Imperial Valley,so an empirical approach was tried
as a first attempt to define aquifer depth zones. This was
accomplished by plotting perforated depth intervals for 143
wells throughout the valley (Fig. 2.22). The hypothesis was
that the drillers would drill to the first good water-bearing
strata and perforate the well casing there. We could then
deduce "preferred" perforated intervals and assume the best
aquifers occur at those depths. Admittedly, this is a simplis-
tic approach, and others interpreting these data may choose
different intervals than were chosen here. Many important
factors were not considered, for example, areal location of well
with respect to depth interval perforated, altitude of the
perforated interval, aquifers occurring below the first good
aquifer intercepted by the driller, etc. However, this is
considered to be a first attempt, within the scope of this
report, and is expected to be modified with further investiga-
tion and analysis.
Shallow, intermediate and deep depth intervals were chosen
from the well perforation interval plot. The shallow water
bearing strata is defined as the depth interval between 24 to 91
m (80 to 300 ft). This corresponds to elevations from 82 m (270
ft) above sea level to 114 m (374 ft) below sea level for the
perforated interval of the wells in our shallow water-bearing
strata category. The intermediate water-bearing strata is
defined as the depth interval between 91 to 457 m (300 to 1,500
ft). This corresponds to a perforated interval elevation range
from 59 m (195 ft) above sea level to about 457 m (1,500 ft)
below sea level for the wells in our sample. The deep water
bearing strata is defined as the depth interval below 457 m
(1,500 ft). This represents strata from about 520 to 4,300 m
(1,700 to 14,000 ft) below sea level for the wells in our
sample. All wells with perforated intervals that overlapped the
interval boundaries were deleted from our sample.
The upper limit of 24 m (80 ft) for the shallow water
bearing strata was chosen to minimize effects of irrigation
water that has passed the tile drain and has become quite saline
by downward percolation through the nearer surface sediments,
which are rich in soluble salts derived in part from fertilizer
and pesticide residues.
There appears to be some justification for these depth
intervals. In plotting the chemical quality data (Section 2.5)
76
-------
WELL NUMBER
- ~* t*- O 00 T -' ~ M „,
~ ~ —
f ^t >a
"T^
>
£
T)
r~
m .5-
^v
TJ
m
3, 30-
~n
O
X
H
m
o
152-
Z
m 305-
•x
>
r-
_
3
~ 1524 -
3048-
..
_•
.
l
^- rrt
- •-• •' '
1
rrt
;
rrt f
1
% n
-
T 10 i*> r"
.
1
•
l»i r^
'
* "
mioroiOioKiiOr«(\j(\jJ
B
oj P
f m
j w oj (\i (\i -
•
•
•
L '"
1 1
i
i
----- - (
* * *
•
•
'.
•
•
, , , 7 1 7 ,7 1 7 i
i
1
1
* "
_. * •
'
•
.'I
i
i
i
i
ij
1
, ,
1
1
|l
i
il'i
•
_
1 1 .
1
i
i >
I
1
1
-
-
10
V)
>
s
T)
r-
m
50 ^
T)
m
100 a)
-n
o
70
j>
H
m
0
500
Z
1,000 m
X
<
>
i—
2
5,000 ~"
0,000
EXPLANATION
EACH HORIZONTAL LINE OR POINT REPRESENTS THE SAMPLE/PERFORATED INTERVAL FOR ONE WELL. ( DATA
FROM HAROT AND FRENCH, 1972)
DEPTH INTERVAL BOUNDARY
24-91 m (80-300ft) —SHALLOW INTERVAL
91 -467m (300-l500ft)— INTERMEDIATE INTERVAL
DEEPER THAN 467m (1500 ft)— DEEP INTERVAL
Figure 2.22 Perforated intervals for wells in Imperial Valley, California,
-------
definite groupings appear to distinguish the shallow and inter-
mediate depth zones. This is particularly evident in the
Langelier-Ludwig diagram (Fig. 2.36), where most of the inter-
mediate waters are grouped along Section AD and the shallow
waters are grouped along Section AB.
Ground Water Flow—
Discussion of ground water flow in Imperial Valley will be
divided into two sections--one on the shallow water-bearing
strata and one on the deeper water-bearing strata. Although we
do refer to shallow (upper) and deep (lower) water-bearing
strata, it is important to note that these classifications must
be used in a very general sense. Their thickness, upper and
lower boundaries and areal extent are not well-defined. Al-
though Dutcher, et al., (1972) suggested four vertical depth
zones for Imperial Valley (section 2.4.2, "Water Bearing Units,"
above), insufficient data is available to discuss flow patterns
in these four depth zones or even to determine how and whether
these zones are confined.
The general direction of flow in the upper and lower water
bearing strata is from the Colorado River, near the southeast
corner of Imperial Valley, northwestward towards the center of
the valley and the Salton Sea. Minor amounts of locally derived
water flow from the mountains on the western and eastern sides
of the valley towards the center of the valley and the Salton
Sea. The limits of water derived from local sources for the
shallow and deep water-bearing units are shown in Figures 2.23 and
2.24, respectively. In the deeper water-bearing strata inter-
ruptions in the general pattern are implied with radial flow
towards geothermal areas since geothermal recharge is assumed
from the deeper aquifer (Fig. 2.24) (Dutcher, et al./ 1972) and
from percolation down fault zones.
Water entering the valley's ground water system eventually
flows into the Salton Sea, is transpired or evaporated on its
way there, or percolates downward to deeper strata.
Direction of Flow in Upper Water-Bearing Strata—Ground-
water flow patterns in the upper aquifer are described by the
water level contours in Figure 2.23 and on Plate 2.1. The ground
water level contours for 1962 and 1964 shown in Figure 2.23 and
those for 1965 shown in Plate 2.1 generally agree very well
with each other, but Figure 2.23 covers a somewhat larger area and
shows slightly more detail and will therefore be referred to in
the following discussion.
Flow occurs in a direction perpendicular to the ground
water level contours at a rate proportional to the steepness of
the hydraulic gradient and permeability; assuming homogenous
isotropic media and in conjunction with topographic relief, the
78
-------
VD
33*1)0'
EXPLANATION
Ground-natei Das in
Dashed where appionuiateiy located;
Dotted where concealed, queried
wheie douDtful
+10--? —
Hater-level contours
Snours altilude ol water level in
shallow aquifer system for 1962
and 1964, Dashed where aapioiimately
located queued Nheie douDtlul
Contour inteival, in feet, is
variable. Datum is mean sea level
Line dividing source ol watei derived
from local mountains and walei
flenved from Colorado Rivei area.
piiof to jrnpoiiation of watei
Figure 2 23 Ground water level contours of shallow aquifer system, 1962 and 1964,
in Imperial and Mexicali Valleys (Dutcher, et al.,1972)
-------
00
o
--0-;
T.
EXPLANATION
O
\ °«,
I KNOWN GEOTHERMAL ANOMALIES
• v
" •""' =)
- .. Ji?i
*4-i—i!—K
?.' (DIAMETER PROPORTIONAL TO APPROXIMATE SIZE OF
KNOWN ANOMALY )
INFERRED DIRECTION OF GROUND- WATER MOVEMENT
IN DEEP AQUIFER SYSTEM
CONJECTURAL LOCATION Of LINE DIVIDING SOURCE
OF WATER DERIVED FROM LOCAL MOUNTAINS AND
WATER DERIVED FROM COLORADO RIVER AREA
20 30 (km)
Figure 2.24 Inferred direction of movement in the deep water-bearing strata
to generalized areas of known geothermal, anomalies in Imperial
and Mexicali Valleys. (Dutcher, et al.,1972)
-------
hydraulic gradient can give an indication of aquifer properties.
In areas of low relief, steep hydraulic gradients may indicate a
low permeability aquifer (or higher velocity flow rate), while a
low hydraulic gradient may indicate a more permeable aquifer (or
a lower velocity flow rate). This trend can be generally seen
by referring to the ground water level contours in the southeast
corner of Imperial Valley and comparing them to the contours in
the north - central part of the valley. The contours in the
southeast are spaced further apart than those in the north
central part, indicating that the sediments in the north-central
part may be less permeable than those in the southeastern part.
Lithologic evidence shows that the sediments of Imperial Valley
are, in fact, coarsest near the crest of the Colorado River
Delta in the southeastern part of the valley and finer towards
the center of the valley (Merriam and Bandy, 1965). Since
coarse sediments are generally more permeable than finer sedi-
ments, this lithologic evidence corroborates the water level
contour implication. The water level contour implication is
further supported by pump tests resulting in the highest meas-
ured permeabilities in the southeastern part of the valley and
low yields in the central valley (Loeltz, et al., 1975, p. 15).
From the Yuma area, ground water flows westward. Before
irrigation began, the ground water divide between waters flowing
to the Salton Sea and waters flowing to the Gulf of California
was apparently around the axis of the Colorado River Delta.
This axis runs from the Yuma-Pilot Knob area southwest, about
midway between the international boundary and the present course
of the Colorado River. Ground water south of the axis flowed
towards the Gulf of California and that to the north of the axis
flowed towards the Salton Sea. After the influence of irriga-
tion the ground water divide appears to have migrated northward
to the Ail-American Canal. This is apparent from the ground
water level contours on Figure 2.23, which indicates most of the
ground water in the shallow aquifer south of the Ail-American
Canal will flow towards the Gulf of California, and water north
of the canal will flow towards the Salton Sea. Some of the
shallow aquifer water will also flow southwest and then north-
west west of the mapped trace of the Imperial Fault.
It can also be seen that the hydraulic gradient increases
towards the center of the valley from essentially zero near the
apex of the Colorado River Delta between Yuma and Pilot Knob to
about 3.4 m per km (18 ft per mi) in the east central portion of
the valley, then down to about l.lm per km (6 ft per mi) just
south of the Salton Sea.
In the southwestern part of the valley all the ground water
is derived from local sources and flows towards the northeast
(Fig. 2.23). The highest water elevation in the southwestern
part of the valley is 85 m (280 ft) above sea level near the
base of the Peninsular Range.
81
-------
The highest groundwater elevation contour on the map
appears in the Santa Rosa Mountains in the northwestern portion
of the valley and is 91 m (300 ft) above sea level. From this
high, water flows east or south and then east. This part of the
map also shows the steepest hydraulic gradients of 11 to 4.5 m
per km (60 to 24 ft per mi).
Evidence of groundwater barrier effects in the shallow
water-bearing strata are apparent only on the Algodones and
perhaps Elsinore Faults (Fig. 2.23). The section of the Elsi-
nore Fault in the southwestern portion of the valley shows about
a 12 m (40 ft) elevation difference across the fault. On the
west side of the fault the groundwater level elevation is about
70 m (240 ft) and there are locally derived very low salinity
waters, while east of the fault the groundwater level elevation
is about 60 m (200 ft) and the water is markedly more saline.
The Algodones Fault section in the southwest of Yuma shows
groundwater level elevation differences of about 6 m (20 ft)
across the fault.
Direction of Flow in the Deeper Water-Bearing Strata—
Insufficient data isavailableto construct a piezometric sur-
face map for the deeper water-bearing strata. Therefore, the
direction of flow is inferred from a conceptual model of the
groundwater system and its relation to the geothermal convec-
tion cells (Fig. 2.31) (see "Groundwater Model of Imperial
Valley Geothermal Systems" below).
The trend of the flow direction in the deeper water-bearing
strata is similar to that in the shallower strata. That is,
north of the international boundary, groundwater generally
flows towards the Salton Sea from the Colorado River and from
the mountains on the eastern and western margins of the valley
(Fig. 2.24). In the Mexicali Valley, south of the international
boundary, deeper groundwater flows towards the Cerro Prieto
geothermal field. The difference in flow patterns between the
shallow and deep strata appears in the larger area recharged
from local meteoric water and in the suggested flow patterns.
around the geothermal anomalies in the deep strata (Fig. 2.24).
Ground water flow in deeper water-bearing strata is thought to
be radial inward toward each of the geothermal fields. The
larger the field, the more area this radial flow pattern will
affect. Some groundwater in the deeper strata is also thought
to flow upwards to shallower depths.
Recharge—
The Colorado River is the most important source of recharge
in Imperial Valley (Dutcher, et al., 1972) with minor contribu-
tions from local precipitation, runoff and tributary underflow.
Only a small part of this recharge reaches the Salton Sea as
continuous flow through aquifers, with a large part flowing
downward to the deep geothermal convection cells and the re-
mainder evaporated or transpired from the surface.
82
-------
Colorado River water enters the groundwater system as
underflow, canal leakage and irrigation water. In the past, the
Colorado River has flowed into the Salton Trough. In these
times the river provided water to the Imperial Valley, as it did
during the canal breaks from 1904 to 1907, when the present-day
Salton Sea was formed by filling of the Salton Trough. When the
Colorado River is flowing into the Gulf of California, the two
main areas where groundwater enters the valley as underflow are
beneath the alluvial section between the Cargo Muchacho
Mountains and Pilot Knob, and beneath the Mexicali Valley.
Irrigation recharge to the shallow aquifer started in 1901.
More than 174 x 103 ha (430,000 acres) are irrigated in Imperial
Valley/ and leakage from the irrigation canals as well as water
applied in excess of crop requirements contributes to the natu-
ral recharge. However, much of the excess water applied to
crops is intercepted and removed from the groundwater system by
the tile drain network underlying the irrigated areas.
Use of the Ail-American and Coachella Canals significantly
increased groundwater recharge. The All-American Canal became
the sole conveyance for Colorado River water to the valley in
1942, and in 1948 the Coachella Canal was added to service the
lower Coachella Valley. These canals, as well as their many
tributary canals throughout the irrigated areas of the valley,
supply much recharge. These canals are unlined and flow across
much permeable, sandy ground, especially in the eastern part of
the valley (see "Recharge by Imported Water," below). The exact
rate of canal leakage cannot be determined. Loeltz, et al.
(1975) estimated the recharge to East Mesa at about 8.6 x
105 ha-m (7 million acre-ft) through 1967. They also estimated
that the Coachella Canal contributed about 3.3 x 10s ha-m
(2.7 million acre-ft) from 1950 through 1967 and the All-
American Canal contributed about 5.5 x 105 ha-m (4.5 million
acre-ft) through 1967. The water imported in this manner is
eventually discharged to the tile drains and through natural
discharge areas.
Tributary underflow plays a very minor role compared to
recharge by imported water. Tributary recharge receives its
greatest contribution from the Mexicali Valley and Carrizo and
San Felipe Creeks, with much less from Pinto and Coyote Washes.
This all totals to less than 2.5 x 103 ha-m/yr (20,000
acre-ft/yr).
Precipitation and runoff provide a very minor source of
recharge in Imperial Valley. Direct infiltration occurs only on
the higher alluvial slopes of the mountains bordering the south-
western part of the valley. Some infiltration along washes and
stream beds discharges to the central valley or Salton Sea. The
total contribution of recharge due to precipitation and runoff
is less than 1.2 x 103 ha-m/yr (10,000 acre-ft/yr).
83
-------
Recharge by Imported Water—The groundwater level contours
in Imperial Valley as represented in 1962 and 1964 (Fig. 2.23)
or 1965 (Plate 2.1) do not represent a natural groundwater
system but rather one showing marked effects of artificial
recharge due to irrigation. The recharge due to irrigation
originates from the Colorado River and flows throughout the
valley in many miles of unlined irrigation canals. Some of the
canals are up to 60 m (200 ft) wide, and the groundwater levels
beneath them show great rises due to infiltration of water from
the canals. The network of canals is dense enough in Imperial
Valley to raise the regional water table significantly, as well
as the water level just beneath and around the canals. Figure
2.25 shows the change in water levels in East Mesa during the
period 1939-60. This figure illustrates the marked water
level increases of over 21 m (70 ft) along the Coachella Canal
and over 12 m (40 ft) along the All-American Canal since they
started operating in 1948 and 1942, respectively. The change in
groundwater level elevation has been small along the East
Highline Canal (Loeltz, et al.,1975), which runs north-south
along the boundary of the lakebed deposits of the main valley
area. This contrast in groundwater level change between the
East Highline, All-American and Coachella Canals may be due to
the tile drain system of the irrigated main valley area directly
conducting the leaked, imported water to outlet channels.
The highest groundwater level elevations to the east of
Imperial Valley are shown in the groundwater mound under the
Yuma Mesa area, south of Yuma. The elevation of this mound was
over 49 m (160 ft) in 1962-64. It is interesting to note the
contrast between this mound and the groundwater level contours
for 1939 in this area (Fig. 2.26) which shows a southerly slop-
ing surface going from 38 m (125 ft) at the Colorado River to
about 27 m (90 ft) south of Upper Mesa and east of the Algodones
Fault. This mound is a result of a combination of two factors.
First, irrigation of citrus groves in this area causes extensive
recharge, and second, the recharge area happens to coincide with
a subsurface silty aguitard layer that keeps the groundwater
table elevated in the form of a mound (Olmsted, pers. comm.,.
1977).
Evidence of the groundwater barrier effect of the Algo-
dones Fault is apparent from the groundwater level contours of
both periods; however, the elevation difference before irriga-
tion commenced was only 1.5 to 3 m (5 to 10 ft), while it rose
to about 6 m (20 ft) by 1964.
The rising groundwater levels in Imperial Valley have
lowered the hydraulic gradient westward from the Colorado River
(Olmsted, et al., 1973, p. H84). This effect can be seen by
comparing average water level contours in 1939 for the Colorado
River Delta region (Fig. 2.26) with the 1962 and 1964 water
level contours for Imperial Valley (Fig. 2.23). For example,
84
-------
Lines of equal change in water level
Dashed where approximately located,
Interval ID feet
Hydrology by 0. J. Loeltz
Figure 2.25 Change in groundwater levels in East Mesa,
1939-60. (Loeltz, et al.,1975)
85
-------
00
CARGO
MUCHACHO
MTS <
LAGUNA J
\ I MTS I [
SOUTH GIL A VALLEY'V ' \ V
EXPLANATION
Water-level contour
S/lii/i--' nllililil,- ,il if.ili-l- I: I'll
, . . ,
l),i-„!, I ,;,! : „:,,/
111 ii'i-i iliiinm /.i nii-iin xr-fi /.!•<•/ Alluvial rsrariimi'tit
. r I ii ill
rea of shallow heorock
/(,,//,,/ „•/!, IV ,;,,,,;;,l,,l
10 15 (Kilometers)
Mountains and lulls
Data for Mexirali Valley provided by the Mexican Section. International Boundary and Water Commission.
Figure 2.26 Average groundwater level contours in 1939 in the Colorado River Delta
region. "(Olmsted, et al.,1973)
-------
the hydraulic gradient in 1939 from the Colorado River near Yuma
westward to the north facing apex of the 130° bend in the All-
American Canal, between Pilot Knob and the Coachella Canal, was
about 0-59 m per km (3.1 ft per mi). The hydraulic gradient for
the same area using the 1962 and 1964 data is essentially zero.
The gradient in an area midway between the Ail-American and
Coachella Canals, an area that would be somewhat less influenced
by the rising water table directly under a canal, was about 0.51
m per km (2.7 ft per mile) for 1939 and about 0.28 m per km (1.5
ft per mile) for 1962 and 1964.
Lowering of the hydraulic gradient in this manner reduces
the velocity and amount of underflow from the Colorado River
into Imperial Valley. At the same time the groundwater supply
and water table elevations are being increased through addition
of irrigation waters at the surface. So in essence the natural
system of groundwater recharge for the shallow aquifer is being
drastically altered by the man-induced effects of the irrigation
system. It is transferring the recharge paths from Colorado
River underflow to infiltration from the surface downward and
then north and westward. Suggestions of this change in recharge
source areas can also be seen by comparing the groundwater
level contours for 1939 (Fig. 2.26) with those for 1962 and 1964
(Fig. 2.23). In 1939 the v- shaped contours around the Colo-
rado River are much more pronounced than those on the later map.
These downstream pointing V's represent a high elevation
groundwater front. In the later map the V- shape contours
have formed around the Ail-American Canal, and to some extent
the Coachella Canal, indicating that the high fronts have mi-
grated from the Colorado River to the irrigation canals.
Groundwater Discharge—
Although much Imperial Valley groundwater discharges into
the Salton Sea, all water that actually leaves the Salton Sea
Drainage Basin must leave through evaporation or evapotran-
spiration. (These processes are discussed in Section 2.1.3 and
the subsection "Outflow" in Section 2.4.3 below).
Groundwater discharge to the Salton Sea occurs mainly
through an extensive tile drain system which lies several feet
below the surface of the irrigated areas. This network dis-
charges about 1.2 x 105 ha-m/yr (1 million acre-ft/yr) of ground-
water and surface waste-water into the Salton Sea. Some of the
discharge from the drains has moved upward from deeper aquifers,
especially near the east edge of the irrigated area.
A similar mechanism occurs under the New and Alamo Rivers
near the Salton Sea. The groundwater level contours approach-
ing the elevation of the topographic contours on Plate 2.1
indicate an upward flow of groundwater here. This upward
leakage from the shallow aquifer averages a few thousand ha-m/yr
(few tens of thousands of acre-ft/yr).
87
-------
Minor discharge is provided from springs, seeps and wells.
Many springs and seeps are found to the northeast of the Salton
Sea, paralleling the San Andreas Fault Zone. A few, with smal-
ler flows, are found southwest of the Salton Sea. Some are
found downstream from the Coachella Canal and are fed by water
from the canal. The total discharge from springs and seeps, not
counting that due to seepage from the Coachella Canal, is esti-
mated to be only a few hundred ha-m/yr (few thousand acre-ft/yr).
Origin of Groundwater—The quantity of groundwater de-
rived from the Colorado River is much greater than the quantity
derived from local sources for all areas and depth zones in
Imperial Valley except West Mesa (Butcher, et al.,1972). Lines
dividing the source of water derived from local mountains and
those derived from the Colorado River are shown in Figures 2.23
and 2.24 for the shallow and deeper water-bearing strata, re-
spectively. Comparison of these lines shows a larger area of
local recharge for the deeper aquifer. However, the quantity of
recharge from local sources into the deep water-bearing strata
under the Sand Hills, East Mesa and main valley areas is still
much less than the quantity derived from the Colorado River.
Dutcher, et al. (1972) have estimated the percentage of
recharge by local precipitation and Colorado River water for
their four depth zones and four areal subunits (Table 2.4).
They estimate 38% of total groundwater in Imperial Valley is
from local sources and 62% is from the Colorado River. Nineteen
percent of the total groundwater in storage in Imperial Valley
underlies West Mesa. All of this water is derived from local
meteoric sources. The Sand Hills area contains 17% of the total
groundwater in storage in the valley and 13% of this is locally
derived. For the East Mesa area, which contains 25% of the
total groundwater in storage, only 6% is of local origin. In
the main valley area, with 38% of the total water in storage,
39% is from local sources.
In the Sand Hills area, the percentage of locally derived
groundwater varies with depth, between 11% and 15% down to
about 2,400 m (8,000 ft). Essentially no recoverable ground-
water occurs below 2,400 m (8,000 ft) in the Sand Hills area.
For the East Mesa area, 5% to 7% of groundwater is from local
sources to depths of about 2,400 m (8,000 ft). But, below
2,400 m (8,000 ft) there is no contribution from local sources.
In the main valley area the percentage of locally derived ground-
water goes from 41% to 31% from depth zone 2 down to the basement
complex.
Geothermal fluid in most hot water and vapor-dominated
systems is derived from meteoric water (Craig, et al./ 1956;
Craig, 1963; Craig, 1966). Isotopic evidence shows that this is
probably the case for Salton Sea geothermal fluid (Craig, 1966).
However, south central Imperial Valley and central Mexicali
Valley geothermal fluids are derived from Colorado River water
88
-------
00
vo
TABLE 2.4 SUMMARY OF "USABLE" AND RECOVERABLE WATER IN STORAGE DERIVED
FROM THE COLORADO RIVER AND LOCAL SOURCES
I Estimates in millions of acre-fuftl
Vertical
Stornpre in arenl suliuntts
depth zone Snnil Hills
Zone 1 :
Local
Colorado River
Zone 2:
Local __
Colorado River
Zone 3:
Local
Colorado River
Zone 4 :
Local
Colorado River
Totals :
Local
Colorado River
Percentage of total.:
Local _ _
Colorado River
16
110
2.6
25
5.3
32
0
.1
191
24
Ki7
13
<87
Kast Mesa
6
97
4.7
84
4.8
63
0
19
279
16
263
6
94
Main valley
0
0
75
100
68
102
24
53
428
1(17
201
39
61
Wtst Mesa
119
.9
63
0
29
0
2.4
0
214
213
0.9
100
0
Total
141
208
145
215
107
197
2G
72
1,112
420
692
38
62
Pvrcentatft*
in OH oh
depth zone
31
32
28
9
38
62
Note:
1. Usable water defined as having less than 35,000 mg/1 TDS.
2. Basis for estimating local sources not explained in
original reference.
-------
(Coplen, 1972). Specifically, the geothermal fluids of the
Dunes and East Mesa anomalies (Coplen, et al., 1973) as well as
the Heber anomaly (Coplen, 1976) have been shown to originate
from the Colorado River.
Major studies of groundwater origin in Imperial Valley
have utilized isotope analyses. In order to determine the
origin of the subsurface water by isotope analysis,it is neces-
sary to isotopically characterize all of the possible sources
and then compare these with spring water, well water and geo-
thermal fluid samples. For Imperial Valley five possible
sources are recognized (Coplen, 1972). They are local meteoric
water, ancient or recent Colorado River water, ancestral sea
water from the Gulf of California, water derived from snow melt
in the mountains to the west and north of Imperial Valley and
juvenile water. Juvenile water does not appear to be necessary
to satisfy observed chemical and isotopic relations in geo-
thermal waters (White, 1968 and 1970; Craig, 1966) and is not
considered further as a source for Imperial Valley geothermal
waters. There is also no evidence of ocean water in the ground-
water or geothermal systems in Imperial Valley (Coplen, 1972).
Comparison of well waters and geothermal waters with the remain-
ing sample source waters shows different origins for ground-
water in different parts of Imperial Valley. Coplen (1972)
concluded that local precipitation plays an insignificant part
in central southern Imperial Valley groundwater system, but
much water from the hot springs to the south and east of the
Salton Sea is derived from local precipitation. Coplen (1972)
further states that the observed decrease in 6 O18 ratios with
depth may indicate downward seepage of partially evaporated
Colorado River water from a large lake in recent times; that
groundwater in the south-central part of the valley, the major
groundwater reservoir, is derived from the Colorado River; and
the salt in the Salton Sea water is also derived from the Colo-
rado River. This last conclusion can be reconciled with the
Hely, et al. (1966) statement that the salinity of Salton Sea
water is a result of solution of evaporite deposits on the floor
of the Salton Sink, if we consider the evaporite deposits formed
by evaporation of Colorado River water.
Permeability—
A number of pump tests were conducted,and permeability data
is available for the upper 300 m (1,000 ft) of sediments in
Imperial Valley. Pump test sites are shown in Fig. 2.10, and
pump test data is presented in Table 2.5.
The results of these pump tests show a moderate to high
yield in the eastern and western parts of the valley in loca-
tions where wells penetrate from less than one hundred to a few
hundred meters of Colorado River or marginal alluvial deposits.
These wells commonly have transmissivities of several million
liters per day per meter with specific capacity of up to 620
90
-------
TABLE 2.5
RESULTS OF USGS PUMPING TESTS IN
IMPERIAL VALLEY, CALIFORNIA (Loeltz, et al., 1975)
Data Type Interval
Well Owner or name of of tested (ft Yield
(fig. 2.20) test test below land (gpml
surface)
"•v Western
i2S/ 9E-22A2 __ T.M.Jacobs 7-29-63 R 286- 867 1,460
12S/1 1E-18J1 __ LCRP 19 520-64 R 310- 650 160
f 18J2 LCRP19A 5-20-64 R 35-55 45
'MS/11E-32R LCRP8 5-11-62 R 135- 165 250
218- 258
310- 354
390- 416
430- 560
Central
16S/14B-18C Imperial Irrigation 5-9-58 R 140-440 160
District.
17S/15E-10N do _ 5-16-58 R 110- 450 90
Eastern
12S/16E-9A Southern Pacific 7-9-63 R 150-1.000 975
Co. 7 9-63 D 150-1 000 675
15S/18E-15M. LCRP11 5-10-63 R 309- 894 1,000
5-10-63 D 309- 894 1,000
16S/18E-32R LCRP 18 6-29-64 R 140- 630 900
16S/19E-1ID LCRP 12 5-14-63 R 300- 610 990
I6S/20E-31K LCRP6 5-2-62 R 340- 410 1,035
510- 520
5-2-62 D 340- 410 1,035
510- 520
16S/21E-16B R. G. Winder 12-4-62 R 598- 806 1,550
12-4-62 D 698- 806 1,550
1. Type of test; D: drawdown, R: recovery
All wells completed in Quaternary
alluvium. LCRP, Lower Colorado
Specific 2
Draw- capacity Transmissivity
down in gpm computed from
(ft) per foot of testa
drawdown (gpd per ft 1
Imperial Valley
14 100
4 38
8.5 5
13 19
Imperial Valley
86 2
68 1.3
Imperial Valley
43 23
27 25
20 50
20 50
21 43
24 41
12 85
12 85
36 43
36 43
3.
Re
River Project of the USGS
2. Most values significant to only one figure
J*. Indicated average field hydraulic
290,000
100,000
.17,000
130.000
2.200
1,700
62,000
47,000
220,000
220,000
140,000
240,000
850,000
880,000
5630,000
3590,000
1 iabi 1
good
fa i r
poor
•)
Conformant 3 Indicated average •
of test data Reliability field hydraulic
to theoretical of computed conductivity
values transmiasivity (gpd per sq ft)
Excellent Good
Pair Fair
do do
Good Good
Good Good
Excellent Good
Good do
Excellent do
Good do
Good do
Poor Poor
760
300
1,800
480
7
5
73
55
380
380
240
770
10,000
10,000
3,000
2,800
i
Difference between com-
puted transmi ss i vi ty and
considered true
i ty transmi ss i vi ty
<25%
25% to 50%
>50%
conductivity=Test Interval
5. May be too high by a factor of 2
-------
Ipm/m (50 gpm/ft) of drawdown in favorable areas.
The central part of the valley has low yields and trans-
missivity. These range from about 12,000 to 120,000 Ipd/m
(1,000 to 10,000 gpd/ft) down to depths of 150 m (500 ft). Lower
transmissivities at lower depths are suggested by the geology
and generally decreasing porosity with depth (see following
subsection,"Porosity").
The very permeable Colorado River deposits in the southeast
corner of the valley have extremely high yields and transmis-
sivities. Well LCRP 6 (Fig. 2.10) has a yield of over 3,800 1pm
(1,000 gpm) and a transmissivity well over 10,000,000 Ipd/m
(800,000 gpd/ft). Yields in this area are comparable to those
of wells in the Yuma and Mexicali Valleys. It is not known how
far eastward this zone of high transmissivity extends, but
traces of former Colorado River channels indicate it may go for
several miles. From this area the transmissivity decreases to
the northwest, although the yields still remain high. For
example, wells LCRP 11, 12 and 18 (Fig. 2.10) have yields up to
3,800 1pm (1,000 gpm) and their transmissivities range from 1.7
to 3.5 million Ipd/m (140,000 to 240,000 gpd/ft).
One well in the West Mesa area, LCRP 8 (Fig. 2.10), has a
yield of 950 1pm (250 gpm) and a transmissivity of 1,600,000
Ipd/m (130,000 gpd/ft). Two wells in the central part of the
valley have yields of 340 to 600 1pm (90 and 160 gpm) with
transmissivities of 21,000 and 28,000 Ipd/m (1,700 and 2,200
gpd/ft).
Imperial Valley geothermal reservoirs show mostly inter-
granular type permeability, except the Salton Sea field, where
fracture permeability is also present. However, fracture perme-
ability may also be encountered at as yet undrilled deeper
levels of the other geothermal fields in the valley. Pressure
buildup and drawdown analyses from the geothermal wells in the
valley give effective permeability values of the order of up to
a few liters per day per square meter (a few millidarcies to a
few hundred millidarcies).Figure 2.27 shows the correlation
between horizontal and vertical permeabilities measured on core
samples from the East Mesa geothermal field. This plot shows a
variable relation between the horizontal and vertical perme-
abilities, ranging from 5:1 at low permeabilities to less than
1:1 at higher permeabilities. Correlations such as this, and
that shown in Figure 2.30 between porosity and permeability, are
not accurate because of the difficulty in obtaining reliable
core samples for such measurement; however, these correlations
do reflect general trends.
92
-------
1000 r-
U)
UJ
O 100
00
<
UJ
I0
O
h-
cc
UJ
Ky= 1.3832 Kh- 20.4557
I
10
100 1000
HORIZONTAL PERMEABILITY (MILLIDARCtES)
Figure 2.27 Correlation between horizontal and vertical
permeabilities, East Mesa KGRA, Imperial Valley,
California.
93
-------
Porosity—
Plots of porosity versus depth determined from well logs
from the Imperial Valley are shown in Figures 2.28 and 2.29. The
locations of these wells are shown in Figure 2.10. All of these
plots reflect the alternating shale and sandstone layers of the
valley through the step-like increase and decrease of porosity
with depth. Superimposed on these small scale step-like in-
creases and decreases, three of the plots show a distinct trend
of decrease in porosity with depth. This trend is especially
well illustrated by Wilson No. I well plot (Fig. 2.29). The
well is located in the central part of the valley,and the poros-
ity decreases from about 60% at 600 m (2,000 ft) depth to less
than 20% at 2,100 m (7,000 ft) depth. The trend is somewhat
more gradual for American Petrofina well 27-1 (Fig. 2.28), in
the East Mesa area, which generally goes from about 50% porosity
at 600 m (2,000 ft) to about 15% at 3,000 m (10,000- ft). The
composite log from the Salton Sea geothermal area shows large,
somewhat inconsistent variations of porosity with depth (Fig.
2.29). A marked sudden decrease of porosity in these wells
around the 900 and 1,200 m (3,000 and 4,000 ft) depth may indi-
cate the location of the geothermal reservoir capping layer.
The porosity shown on the plot for the Grupe-Engebretson No. 1
well in the south-central part of the valley is more generalized
than the others. The porosity goes from about 35% at 600 m
(2,000 ft)to 10% to 20% around 3,700 m (12,000 ft). In general,
the porosity present in Imperial Valley reservoirs is of inter-
granular type. However, in the Salton Sea geothermal reservoir,
fracture porosity is present. Fracture porosity may also be
present in deeper parts of the other geothermal fields in the
valley. Figure 2.30 shows the correlation between the porosity
and permeability measured from cores from the East Mesa field.
Recoverable Water in Storage—
Rex (1970, p. 14) estimated 2.0 to 5.9 x 108 ha-m (1.6 to
4.8 billion acre-ft) of total water in storage in Imperial
Valley. , Combs (1971, p. 11) revised this estimate to include
only economically exploitable reserves, those between 900 m
(3,000 ft) and 3,000 m (10,000 ft) depth. He used a porosity
depth function from the American Petrofina Salton Trough Pros-
pect No. 27-1 well to calculate total water in storage in this
depth interval at 2.6 x 108 ha-m (2.1 billion acre-ft).
A more detailed, although still extremely rough, estimate
of 1.4 x 108 ha-m (1.1 billion acre-ft) total "usable" and
recoverable water in storage was made by Butcher, et al. (1972).
They defined "usable11 water as that containing less than 35,000
mg/1 TDS regardless of any specific ion concentration. Table
2.4 summarizes the Dutcher, et al. (1972) estimate of "usable"
and recoverable water in Imperial Valley. They divided Imperial
Valley into four vertical depth zones and four areal units which
are defined in the subsection on "Water-Bearing Units"above. As
can be seen from Table 2.4, almost 40% of the total water in
94
-------
u
1
2
3
0
m
TJ
H 4
I
H
m
HOUSA
z
-n 6
m
m
H
7
8
9
10
i i i i i i
AMERICAN PETROFINA
SALTON TROUGH
~ PROSPECT NO. 27-1
SOUTHERN PART OF IMPERIAL COUNTY. CALIF.
* .....j
j=F
: f :
; ^_
tV4*""' 1 1 1 1 1
D 10 20 30 40 50 60 7
2
3
4
i 5
0
m
T3
H
I
O 7
C '
Z
0
"n
m
m
H
~ 9
10
II
0 l2
1 1 1 1 1 1
. ... \
1
1
1
I
1
1
r
N
N
\
1
"""--,
1
1
M. ""
;
(
y
/ THE TEXAS COMPANY
1 GRUPE-ENGEBRETSON NO. 1
--" SOUTHERN PART OF
\ IMPERIAL COUNTY, CALIF.
\
i . ... ."i i i i i i
D 10 20 30 40 50 60 7(
POROSITY (PERCENT)
POROSITY (PERCENT)
Figure 2.28 Porosity versus depth for two wells in southeast Imperial Valley,
(Combs, 1971)
-------
o
1
2
3
o
TJ
H 4
— 1
X
o «-
c 5
CO .
z
Tl 6
m
m
H
^* '
' 7
B
9
°r
(j
1 1 1 1 1 1
STANDARD OIL CO. OF CALIFORNIA
WILSON et.ol NO. 1.
" CENTRAL PART OF IMPERIAL COUNTY. CALIF.
^^ ,
•T1
r5.
i — ,
_
-
^
-
i f\ <"»/"* -y n A r\ c r\ fn ~9
IU C.\J J\J *HJ 3U DU f
POROSITY (PERCENT)
0
l
2
"^
0
m
^0 *T
H
I
—
-H
I 5
O
C
CO
§6
-n
rn
m
— 7
8
9
n IO
\j ' v
(
1 1 1 1 1 1
r-T^ — J
f.-*
~
j
\
"~ "-"——-. ^
— J
tr —
-~ -,
"^* **** '*** •*-.
„ i _
_ _
COMPOS ITE OF DATA FROM
WELLS IN THE
SALTON SEA GEOTHERMAL AREA _
NORTHERN PART OF
IMPERIAL COUNTY, CALIF.
11 i i i i
D 10 20 30 40 50 60 7(
POROSITY (PERCENT)
Figure 2.29 Porosity versus depth for two wells in central and northern
Imperial Valley. (Combs, 1971)
-------
1000
900
BOO
700
600
500
400
300
200
100
90
80
70
60
50
40
30
n
ti
2
ro
a
eg
o
a.
20
10
9
8
7
6
5
4
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
• log K = 14.3520-2.1372
( 0 in fraction)
10
15
20
25
30
35
Core Porositv - %
Figure 2.30 Correlation between core permeability and core
porosity, East Mesa KGRA, Imperial Valley, California,
97
-------
storage is contained in the thicker sediments of the main valley
area, 25% under the East Mesa area, and less than 20% each in
the thinner sedimentary accumulations of the east and west
margin areas. Butcher, et al. (1972) estimate that about 2.5 x
107 ha-m (200 million acre-ft) of the total, or about 18%,is at
temperatures greater than 150°C (302°F). Of these hot waters
65% of the total is in storage beneath the main valley area.
This may be due to the thicker sedimentary accumulations of the
main valley area providing better hydraulic communication with
deeper waters which have possibly been heated at depths closer
to the heat sources. Details of the assumptions, methods and
estimates used by Butcher, et al. (1972) are outlined below.
Butcher's Water Storage Estimates—Butcher, et al. (1972)
made water in storage estimates for water that would be "usable"
and recoverable. The term "usable" water, as defined in the
previous paragraph, was based upon the consideration that it is
presently uneconomic to utilize water with more than 35,000 mg/1
TBS. Also, the lower the TBS the greater proportion of water
that can be blended with desalted water. The criteria of recov-
erability were based on the assumptions that it is possible,
using sound engineering practice, to withdraw water from the
ground over a long period of time; that the physical state of
the fluid and the physical character of the rock are principal
factors in recovery; that no water would be available from
shallow aquifers in the main valley area due to the tile drain
system and that whatever was recovered would only be imported
irrigation water. However, no consideration was given to the
economic feasibility of recovery.
An estimate of the amount of "usable," recoverable water in
storage is computed by multiplying the area of the storage unit
by the thickness of the deposit by the specific yield or total
porosity of the deposit. All of these values are estimates and
approximations based on representative or extrapolated data;
hence the product is even less reliable than the individual
components.
The total thickness of these water-bearing rocks and de-
posits was estimated by Rex (1970) who utilized gravity data
collected by Biehler (1964) and additional seismic data (Fig.
2.8). Well logs confirm Rex's (1970) interpretation. The
distribution of rocks containing more than 35,000 mg/1 TBS was
plotted and contoured areally and superimposed onto the depth to
basement-complex contours resulting in a contoured plot of total
thickness of deposits with usable water (Fig. 2.14). Naturally,
the thickest deposits are in the center of the valley/and they
thin to zero thickness along the east, west and northern margins
of the Imperial Valley sedimentary basin. The contours were not
evaluated southward into Mexicali Valley. One section south
98
-------
of Holtyille has more than 4,600 m (15,000 ft) of sediments
containing "usable" and recoverable water in storage, and another
section north of Brawley has more than 4,000 m (13,000 ft).
Parameters relevant to the amount and properties of recov-
erable water in storage in each depth zone are discussed below.
Water in Storage in Each Depth Zone—(Classification and
characteristics of the four depth zones are described in the
subsection on'Water-Bearing Units," above).
The contour of zero thickness for the deepest zone, zone 4,
encloses an area of about 2,600 sq km (1,000 sq mi) (Fig. 2.15)
and is up to 2,100 m (7,000 ft) thick. It is estimated to
contain 2.3 x 108 ha-m (1.9 billion acre-ft) of rock with 5%
porosity. It was felt by Dutcher, et al. (1972) that most of
the water in this rock would be recoverable since it is hotter
than 149 °C (300°F). This amounts to about 1.2 x 107 ha-m (100
million acre-ft) of recoverable water in zone 4. However, this
specific yield estimate may be somewhat high.
Zone 3, above zone 4, has much more water in storage than
zone 4 since it is much larger and has higher porosity. The
porosity of the rock is about 20%, but due to low permeability
only about 16% of the water in storage is estimated 'to be re-
coverable. About 2.3 x 108 ha-m (1.9 billion acre-ft) of rock
are included in the 4,400 sq km (1,700 sq mi) area of this zone
(Fig. 2.16). Hence, there should be about 3.7 x 107 ha-m (300
million acre-ft) of recoverable water, all at temperatures
greater than 100°C (212°F), in zone 3.
The deposits of zone 2 enclose an area of 4,270 sq km
(1,650 sq mi) (Figure 2.17), and the estimated volume of rock
contained in the zone is 3.5 x 108 ha-m (2.8 billion acre-ft).
It was estimated that the amount of recoverable water or spe-
cific yield of this zone would be about two-thirds of the poros-
ity or 13%. This multiplied by the rock volume gives 4.4 x
107 ha-m (360 million acre-ft) of recoverable water in zone 2.
For the shallowest zone, zone 1, water in storage is esti-
mated from the area, depth and specific yield of each of the
four areal units. The Sand Hills area has an estimated specific
yield of 20% and area of about 1,170 sq km (450 sq mi). The
East and West Mesa areas have an estimated specific yield of 15%
each and areas of 910 and 1,200 sq km (350 and 465 sq mi),
respectively. No water will be recovered from the main valley
area since essentially all the ground water in that area is from
irrigation input. Dutcher, et al. (1972) compute a total of
about 4.3 x 107 ha-m (350 million acre-ft) of "usable" and
recoverable water in storage in zone 1. This total is comprised
of 1.67 x 107 ha-m (126 million acre-ft) in the Sand Hills area,
99
-------
1.28 x 107 ha-m (103 million acre-ft) in the East Mesa area and 1.5
x 107 ha-m (120 million acre-ft) in the West Mesa area.
Again, it is important to emphasize that these estimates
are based on a conceptual model with very limited estimates and
extrapolations. Although the computations and logic may be
sound, the approximations used will certainly be altered in the
future when more detailed data becomes available. These esti-
mates will only serve as a "best guess" until more reliable
computations can be made.
Groundwater Model of Imperial Valley Geothermal Systems—
The relationship between shallow ground water, deep ground
water and geothermal water must be known in order to assess
environmental effects of geothermal development. This includes
knowledge of the mechanisms of recharge and discharge, heat
transfer, fluid flow direction and rate, water chemistry, geom-
etry of ground water reservoirs and aquifers, field boundaries
and the rate and location of fluid extraction and injection.
This knowledge is still being developed,, and presently insuffi-
cient data is available for detailed definition of the deep and
geothermal ground water systems in Imperial Valley. Therefore,
it is necessary to utilize a representative model of the geo-
thermal system that is consistent with the data we have ob-
served. Development of this model is traced below from basic
characteristics to specific Imperial Valley geothermal fields.
In the future, as more data is collected and analyzed, these
models will be altered and improved.
A basic model of geothermal systems contains four basic
features. They are: a natural heat source, a water supply, a
ground water reservoir and a cap rock (Facca, 1973, p. 62). The
heat source in most cases would be of magmatic origin, the water
supply would have to be sufficient to saturate and replenish the
permeable rock or aquifer of the ground water reservoir, and the
cap rock would seal the system to continue convective currents
in the aquifer or at least trap the water long enough for it to
be heated (Fig. 2.31). In this general geothermal convection
system model, ground water in the permeable aquifer is heated by
conductive heat flow through the bedrock from the magmatic heat
source. Since heated water rises, it starts convective currents
within the aquifer beneath the capping and confining formation
above. This heated water may escape through fractures in the
cap rock or through a well piercing the cap rock. Replacement
of water in the aquifer may occur through downward percolation,
from deeper aquifers through fractures or from more distant
parts of the aquifer.
Specific models for Imperial Valley must also consider the
fault systems in the valley, the great variation in salt concen-
tration in geothermal brines, two different meteoric water
sources, up to 6,000 m (20,000 ft) of sands, silts and clays
100
-------
0- C 100" C 200* C 300- C 400" C WO' C
Temperaiyre
Figure 2.31 A. Basic model of a geothermal system. (Facca, 1973)
.:: T:
»- C
CD c
Surface
Channel greatly
exaggerated
A little orir.e escapes upward;
ratios of metals to S, COj,
and H20 decrease in = hale,\
men! sjlfides prec
Circulating
water high in
SOIS relative to
S0l6and enri_
ched inSD by
• Vapor escapes upward; most
HjO and H«S condenses
CDs is enriched by release in
carbonate-silicate reactions X
Hlowir.g water low irSCie
relative toSO16, lowinSD ;
moderately high in CoSC4|
dissolved solids about
35,000 mg/1.
(HjO.COj.HjS)
C^nvecting brine
is high ir. metals;
low in dissolved
IDS about
260,000 mg/1
Zone of CaCO,
Reservoir rocks high in c.w
relative to SO16 and low in SO
FLOW
Co S04preel pi tat ion , \
Causing reduced per_ .
meability.
Zone of SiOz solution
causing increased per-
meability
Zone of heat flow
by conduction and
inflowing water,
>, temperature
\ increases toward
\ convection cell
V
and
\
HEAT
Figure 2.31 B.
Modified model for Salton Sea geothermal system,
showing source of recharge and water quality
changes. (Dutcher, et al.,1972)
101
-------
overlying an igneous and metamorphic basement complex and an
apparently random distribution of geothermal anomalies (Rex,
1970). Conceptual models for genesis of Salton Sea geothermal
fluids have been proposed by Craig (1966), Berry (1966),
Helgeson (1968), White (1968) and Dutcher, et al., (1972). Craig
(1968) proposed that the Salton Sea geothermal brine is formed
by local precipitation leaching down through sediments and
concentrating in the geothermal convection cell. Berry's (1966)
model attributes the concentration of the brines to filtration
of Colorado River source water. Helgeson (1968) believes that
the Colorado River water had been concentrated by evaporation
before the last few hundred meters of sediments were deposited.
White (1968) suggests that rock-water interaction between evap-
orites and ground water produces the hypersaline brines. Re-
charge to the deep geothermal aquifer is from downward percola-
tion of shallow ground water, and this water circulates in con-
vective heat cells below a shale dominant cap rock. Further
concentration is permitted by fluids and gases escaping through
fractures to the surface. Dutcher, et al. (1972) basically
accept White's (1968) model with slight modifications. They do
not require the evaporite deposits for hypersaline brine pro-
duction (Fig. 2.31B).
The Dutcher, et al. (1972) model (Fig. 2.3IB) shows a shale
dominant upper layer overlying a sands tone-dominant fractured
brine reservoir. The interface between these two layers in
Imperial Valley generally appears to be between 600 and 900 m
(2,000 and 3,000 ft) (Dutcher, et al., 1972, p. 31; Meidav and
Sanyal, 1976; Coplen, 1976, p. 25), although it might be only
about 300 m (1,000 ft) at Heber (Meidav, et al., 1975). Recharge
is through downward percolation from shallower aquifers above
the brine reservoir. This inflowing water has low 6018 and 6D
isotope ratios suggesting that the water has not yet been
heated. This model suggests high calcium sulfate and TDS of
about 35,000 mg/1 for the recharge water of the Salton Sea
geothermal field. The downward percolating water is heated, and
its temperature increases as it flows towards the convection
cell. The reservoir rock this recharge fluid enters is high in
6018 and low in 6D. This fluid-rock interaction reduces the
6018 ratio of the rock, and evaporation increases the 6D ratio of
the water in the convection cell. The convecting brine becomes
concentrated by escape of water, carbon dioxide, hydrogen sul-
fide and other vapors through fractures in the dominantly sand-
stone brine reservoir. Most of the water and hydrogen sulfide
vapor condenses in the upward escaping-yapor^ and carbon dioxide
is enriched by release in carbonate-silicate reactions with the
surrounding rock. This sublimination enriches the water in 6D,
and the convecting brine becomes high in metals and low in dis-
solved sulfide and may attain a maximum TDS content up to
385,000 mg/1. Within and around the convection cell hydro-
thermal fluids are precipitating calcium carbonate and calcium
sulfate, which causes reduced permeability in the reservoir
102
-------
while the same fluid is dissolving silica, causing increased
permeability.
Brine that escapes upward reacts with the shale, resulting
in lower ratios of metals to sulphur, carbon dioxide and water.
Metal sulfides are also precipitated. It is a dynamic system,
and all these processes and chemical reactions occur contin-'
uously and simultaneously.
Meidav, et al., (1975) proposed a conceptual model of the
East Mesa geothermal anomaly which explains the occurrence of
high residual gravity anomalies over this field. Similar grav-
ity anomalies have been noted over other geothermal fields in
the valley (Fig. 2.32). According to Meidav, et al. (1975) this
gravity high may be explained by densification of porous rocks
due to precipitation of minerals in the cooler parts of a con-
yecting geothermal system. The top of such a convection system
is shown by the sharp decrease in the temperature gradient in
wells (Fig. 2.33). In the convection cell, the vertical tempera-
ture gradient is very small. In this figure, the static temper-
ature profiles in wells from Salton Sea, Heber, East Mesa and
Cerro Prieto geothermal fields are compared. It is interesting
to note that the top of the convection zone at Heber appears to
be much shallower than that at East Mesa. Also, the Salton Sea
and Cerro Prieto wells dp not show any sign of the onset of
convection within the limits of Figure 2.33. Figure 2.2 shows the
temperature gradient anomalies observed over the geothermal
fields in Imperial Valley. Geothermal fields in the valley are
characterized by gravity, electrical resistivity and temperature
gradient anomalies.
Butcher, et al., (1972) suggest that the difference in brine
concentration between the Salton Sea geothermal field and other
geothermal fields to the south is due to a lower concentration
of salts in the recharge water. That is, the recharge water for
the Heber area, for example, may contain 1,500 to 2,000 mg/1
TDS. If this is concentrated about ten times by the convection
cell, it would result in a brine with about 20,000 mg/1 concen-
tration. A similar mechanism for the Salton Sea geothermal
field, assuming a recharge with 25,000 to 35,000 mg/1 TDS, will
result in a brine concentrated to hundreds of thousands of
milligrams per liter TDS.
2.4.3 Hydrologic Budget
The hydrologic budget of an area relates the total amount
of water entering a drainage basin to water use and the total
amount of water leaving the drainage basin. A general hydro-
logic budget for Imperial Valley is presented below, followed by
more detailed discussions of Salton Sea drainage basin inflow
and outflow.
103
-------
o
it*.
CONTOUR INTERVAL I MGAL.
1000 MGALS ADDED TO ALL GRAVITY READINGS
Figure 2.32 Complete Bouguer anomaly map of the Imperial Valley. (Biehler, 1971)
-------
100
9000
150
200
Temperature (°F)
250 300
350
400
450
DUNES (DWR No.I)
HEBER (J.D.JACKSON Jr. No. I)
SALTON SEA (ELMORE No. I)
HEBER (G.T.W. No.3)
E. MESA (6-I)
E. MESA (8-I)
CERRO PRIETO
50
IOO
200
Temperature (°C)
• 500
-1000
-1500
CL
UJ
Q
-2000
-2500
Figure 2.33 Static temperature profiles in geothermal wells
from the Salton Trough.
105
-------
The Imperial Valley Irrigation and Coachella Valley Consol-
idated Water Districts usually import about 370,000 ha-m (3
million acre-ft) of Colorado River water per year for their
domestic and agricultural needs. During 1961-1963 the gross
annual diversion to nearly 200,000 ha (500,000 acres) in the
Imperial and Coachella Valleys was 444,000 ha-m (3,603,000
acre-ft), or 2.19 ha-m per ha (7.2 acre-ft per acre) irrigated.
This rate of use, however, is affected by conveyance losses
averaging 36,000 ha-m (290,000 acre-ft) annually below Pilot
Knob and by discharge of all unconsumed water to the Salton Sea.
These large losses are not included in the following water
budget for irrigated land in Imperial Valley:
Measured inflow 377,000 ha-m (3,056,000 acre-ft)
Measured outflow 157,000 ha-m (1,270,000 acre-ft)
Residual 220,000 ha-m (1,786,000 acre-ft)
The residual represents an average consumptive use on 174,000 ha
(432,000 acres) of 1.25 ha-m per ha (4.1 acre-ft per acre),
including uses in unplanted areas within the irrigated tract. A
similar computation for the Coachella Valley indicates consump-
tive use of 1.16 ha-m per ha (3.8 acre-ft per acre).
Inflow—
Most surface water is derived from the Colorado River
through irrigation runoff. It amounts to 123,000 to 154,000
ha-m (1 to 1% million acre-ft) annually.
Inflow to the Salton Sea consists of discharge from surface
channels, ground water seepage directly to the Salton Sea and
precipitation on the water surface. This water flows perenni-
ally to the Salton Sea via the Alamo, New and Whitewater Rivers
and many drains and ditches. Ninety percent of the inflow comes
from the Imperial Valley, primarily via the Alamo and New
Rivers, and 10% comes from the Whitewater River and minor chan-
nels in the Coachella Valley. Average annual inflow for 1961-63
from the Alamo and New Rivers and 30 other channels was 156,700
ha-m (1,270,000 acre-ft). Average annual inflow for the same
period was 13,600 ha-m (110,000 acre-ft) from the Whitewater
River and 18 drains in the Coachella Valley.
Salt Creek, on the eastern side of the Salton Sea, has a
small perennial base flow into the Salton Sea. The Coachella
Canal crosses the lower part of the Salt Creek Basin and several
other small drainage basins southeast of Salt Creek. Only a few
percent of the flow in Salt Creek comes from runoff; the major-
ity is from canal seepage.
San Felipe Creek, which flows to the southwest shore of the
Salton Sea, drains an area of more than 2,600 sq km (1,000 sq mi)
106
-------
including much mountainous area and some small tracts irrigated
with local water supplies. A small base flow persists only
during the winter months and storm runoff usually accounts for
90% of this flow.
Surface inflow to the Salton Sea from areas not irrigated
is quite small during most years but will increase during
periods of heavy storm intensity. The Alamo and New Rivers have
average annual flows of over and less than 62,000 ha-m (500,000
acre-ft), respectively. The Whitewater River annually contrib-
utes less than 12,300 ha-m (100,000 acre-ft) of water to the
Salton Sea.
Outflow—
Evaporation, at a rate of approximately 1.8 m (5.8 ft) per
year, is the only outflow from the Salton Sea. This figure is
from a detailed study of the hydrology of the Salton Sea drain-
age basin in 1961-62 by USGS in conjunction with other agencies
(Hely, et al. 1966). In this study water budget, energy budget,
mass transfer and evaporation pan methods were used to determine
evaporation rates from the Salton Sea. The water budget method
utilizes a relationship- between evaporation, precipitation,
runoff and change in water storage for a hydrologic unit. The
equation is:
AV = I + I + P
t> y
- E
where
AV
I
= change in volume
= inflow in surface channels
a
I = inflow as ground water seepage
P = precipitation on the water surface
E = evaporation
The energy budget method accounts for all heat energy
reaching, stored in and leaving a water body. The objective is
to determine the amount of energy utilized in the evaporation
process and the quantity of water evaporated. The energy budget
for a body of water is expressed as a function of incident and
reflected solar radiation, incident, reflected and emitted long
wave radiation, energy in the water body, energy used and ad-
vected by evaporation and conducted energy.
The mass transfer method relates evaporation from a water
surface to the product of windspeed multiplied by the humidity
gradient of the air; the equation is:
107
-------
E = NM
-------
The development of geothermal wells near the Salton Sea
could result in brine disposal problems. Establishment of
evaporation basins for geothermal brine disposal, at altitudes
above the Salton Sea surface, might result in saline residue
contaminating usable ground water. Geothermal brines could not
be pumped into the Salton Sea since this would raise the salin-
ity of Salton Sea water. Therefore, geothermal power utiliza-
tion must include a satisfactory waste disposal system.
Use of Colorado River water in the Salton Sea Basin in-
volves substantial losses during transport. Seepage from the
Coachella and All-American Canals averages 40,000 ha-m (330,000
acre-ft) annually. Canal lining or sealants may be necessary to
prevent these losses in the future. However, part of the seep-
age recharges aquifers, and irrigation tract runoff maintains
the water level in the Salton Sea. Considerable excess dis-
charge is also necessary to maintain low soil salinity and
thereby high agricultural productivity. A decrease in inflow to
the Salton Sea would gradually increase salinity and recede the
shoreline thus reducing the recreational value of the area.
Given present irrigation and drainage arrangements, no
harmful salt quantities are accumulating in parts of Imperial
and Coachella Valleys irrigated by the imported Colorado River
water (Irelan, 1971). However, the imported water's mineral
load must be carefully monitored so the current salt balance can
be maintained.
2.5 CHEMICAL CHARACTERISTICS OF GROUND WATER
Knowledge of currently existing chemical characteristics of
ground water is essential to define a baseline for future com-
parison. An integral part of any monitoring methodology devel-
oped will be an accurate definition of the starting, or base-
line, conditions. The following results of the ground water
quality investigation describe the occurrence and distribution
of ground water types in Imperial Valley. The methods explored
in this study will greatly assist in evaluating their applica-
bility in establishing a baseline condition in any geothermal
area.
Water quality data for 145 wells in Imperial Valley were
compiled and plotted in three depth intervals using modified
Stiff diagrams, Langelier-Ludwig diagrams and three-dimensional
surface plots of the single-chemical parameter contours. The
depth intervals, chosen from a plot of well perforation inter-
vals (Fig. 2.22), are shallow, from 24 to 91 m (80 to 300 ft),
intermediate, from 91 to 457 m (300 to 1,500 ft) and deep,
depths greater than 457 m (1,500 ft).
109
-------
The modified Stiff diagrams show the areal distribution of
five distinct water types: a sodium chloride water, a high
sulfate water, a sodium chloride with high sulfate and/or magne-
sium water, a sodium chloride with high calcium water, and a
sodium bicarbonate water. The Langlier-Ludwig plot shows two
distinct chemical groups of water. One group, essentially along
the Na+K axis, contains a high proportion of shallow depth
interval points, and the other group, essentially along the
SO..+C1 axis, contains a high proportion of intermediate depth
interval points. Several structural features, such as the
Elsinore Fault trace, the trend of the Calipatria Fault and
several geothermal anomalies, can be deciphered from the single
parameter contour plots.
Objectives and Limitations—
The objective of these representations of water quality is
twofold. First, it is intended to represent baseline chemical
characteristics of Imperial Valley waters, and second, it is
anticipated that some insight into aquifer geometry and distri-
bution of ground water might be derived from the graphic
displays.
This phase of the study is largely descriptive and data
presented in this report provides a useful vehicle for synthe-
sis, analysis and interpretation of baseline ground water con-
ditions and some aquifer relations in Imperial Valley.
Within the scope of the project the limitations of this
approach appear in two main areas: first, data availability
limitations, and second, limitations of the interpretive tech-
niques. These limitations are detailed below.
Data acquisition was terminated when a point of diminishing
return was reached. That is, the water quality data search was
extensive, but not exhaustive. The sources used include:
"Selected Data on Water wells, Geothermal Wells and Oil
Tests in Imperial Valley, California," by W. F. Hardt and
J. J. French (1976), a compilation of ground water quality
data for 436 wells; this source contains analyses that have
previously appeared in many separate publications. The
data published in this report was also available in digi-
tized format on magnetic tape which was used for the three-
dimensional surface plots of single -chemical parameter
contours.
"Chemistry of Thermal Water in Selected Geothermal Areas of
California," by M. J. Reed (1975), a report that includes
chemical analysis of ground water from 48 wells, mostly
from the artesian aquifer in Imperial Valley.
110
-------
"Lawrence Berkeley Laboratory Brine Data File," by s. Cosner
and J. Apps, (1977), a compilation including 27 chemical
analyses of geothermal well waters in Imperial Valley.
"Geotechnical Aspects of The Environmental Iitpact of Geothermal Power
Generation at Heber, Imperial Valley, California," by
Geonomics (1976), which includes analyses of a number of
geothermal wells in the Heber and Cerro Prieto geothermal
areas.
The chemical analyses used in this report are not reproduced
here since they are available in the above-mentioned publica-
tions. The sample numbering system employed in this report
allows easy reference to original sources and is shown on Plates
2.3 and 2.8.
The criteria used to select the ground water quality data
for inclusion in this study were:
1) sample depth interval must be specified, and
2) sample depth interval must fall completely within one
of the preliminary water — bearing strata depth
intervals.
Wells with no specified sample depth interval were excluded
because it would make correlations of chemical quality with
water bearing strata more difficult, if not impossible. Analy-
ses of ground water samples which overlapped water—bearing
strata depth intervals were excluded for the same reason.
As a result of these limiting criteria the total number of
analyses included in this survey is 145. This consists of 55
wells in the shallow water—bearing strata, 64 wells in the
intermediate water—bearing strata, and 26 wells in the deep
water-bearing strata.
The quality of the chemical analyses was not evaluated.
This would have proven to be an extremely difficult, time-con-
suming and often arbitrary task. The work was conducted on the
assumption that the chemical analyses were reliable, unless
discrepancies became apparent. It is felt that this was the
best way to approach this task, within the scope of the project.
The Stiff and Langelier-Ludwig graphical techniques are
commonly used in ground water quality studies. Each of these
methods has limitations with respect to interpretation and
aquifer correlations. Stiff diagrams permit representation of
the areal distribution of waters, but it is difficult to deline-
ate chemical groupings and mixing relationships from them. .They
would be most useful when comparing only a few characteristic
water types within a limited concentration range. Because the
111
-------
waters in Imperial Valley have such a wide range of concentra-
tions, from a few hundred to over a quarter of a million milli-
grams per liter TDS, it was necessary to modify the Stiff dia-
grams to represent percent reactance instead of milliequivalents
per liter. This limited the usefulness of the diagrams since
relative concentrations would not be seen, but the salinity
circle overlay plots somewhat overcome this deficiency.
The Langelier-Ludwig plots depict chemical groupings of
waters and can represent, with their salinity cross sections,
mixing and rock-water interactions, as well as concentration and
dilution.
The approach taken in this report is an assessment of base-
line data which is largely descriptive in nature. The methods
used provide strong suggestions of aquifer-water correlations
and a useful basis for comparison with future water chemistry
surveys to determine changes from a baseline condition. From
this point intensive study of the data by sophisticated statis-
tical, computer and critical analytic techniques will be neces-
sary to further define the relationships of different waters and
aquifers.
Description of Methods—
Three basic graphical display techniques were utilized to
establish baseline water quality conditions in Imperial Valley
and to define the areal and vertical distribution of distinctive
ground water types and aquifers. These techniques are modified
Stiff diagrams, Langelier-Ludwig plots and single -chemical
parameter plots. Details of these methods are described below.
Modified Stiff Diagrams—Stiff diagrams (Stiff, 1951) are
closed polygons which show relative concentrations of major
ionic constituents of water (Fig. 2.34; Plates 2.4, 2.6 and
2.8). Water with similar chemical characteristics will have
Stiff diagrams with similar shapes. The modified Stiff diagrams
used for this study are plotted with ionic concentrations in
percent reactance in order to accommodate the great range in
salt concentrations, from about 700 mg/1 to over 360,000 mg/1.
For each diagram the well number, sample depth interval and TDS
in ppm are shown by adjacent numbers. The Stiff patterns them-
selves are plotted on a base map to show the areal distribution
of different types of waters.
For this study the Stiff diagram is constructed with a
vertical line bisecting three horizontal axes (Fig. 2.34; Plates
2.4, 2.6 and 2.8). The axes to the left of the vertical line
represent the major cations—from top to bottom, calcium, magne-
sium and sodium plus potassium—in percent reactance from zero
to one hundred. Similarly, the major anions—bicarbonate plus
carbonate, sulfate and chloride-- are represented from top to
bottom on the right side of the diagram. The percent reactance
112
-------
A. Typical Simple
Sodium Chloride Water
B. Typical Sodium Chloride
Water with High Sulfate
and/or Magnesium
9540
15200
C. Typical Sodium Chloride
Water with High Calcium
D, Typical High Sulfate
Water
503
15,430
E. Typical Sodium Bicarbonate
Water
790-f
950
1760
850
EXPLANATION
MODIFIED STIFF DIAGRAMS
IN PERCENT REACTANCE
,WELL NUMBER
SAMPLE
DEPTH
INTERVAL
No +
DOT
SIGNIFIES
NO K-VALUE , TATA. -,0-,-..,™
GIVEN TOTAL DISSOLVED
GIVEN ' SOLIDS (mg/i)
SAMPLE DEPTH CODE:
D SHALLOW INTERVAL(80-300ft)
A INTERMEDIATE INTERVAL(300-l500ft)
ODEEP INTERVAL (isooft)
Figure 2.34 Modified Stiff diagrams for characteristic
Imperial Valley groundwaters.
113
-------
values are calculated separately for cations and anions as the
individual ion concentration expressed in milliequivalents per
liter divided by the respective total anion or cation concentra-
tion expressed in milliequivalents per liter.
These diagrams differ from those originated by Stiff (1951)
in that he used milliequivalents per liter for the scale and had
the ions represented in a different order. To accommodate for
the loss of expression of concentration, salinity circles were
plotted as an overlay to the modified Stiff diagrams (Plates
2.5, 2.7 and 2.9). These circles are drawn to represent the TDS
concentration, with the salinity circle's diameter proportional
to the logarithm of the TDS concentration. That is, a circle
that has twice the diameter of another will have a TDS concen-
tration ten times as great. The logarithmic scale was neces-
sary to include the great range of TDS values in the Imperial
Valley ground water. Average sample interval elevations are
plotted with the salinity circles for added information.
Langelier-Ludwig Diagrams—The Langelier-Ludwig (L-L) dia-
gram ~TLang^ITeTan^LudwTgT~ 1942) (Figs. 2.35 and 2.36) is
similar to the rhombohedral section of the Piper diagram (Piper,
1944). It is a square plot of percent reactance of alkalic
cations (Na+K) ascending from 0 to 100 on the left-hand vertical
axis and hardness cations (Ca+Mg) descending from 100 to 0 on
the right—hand vertical axis (Fig. 2.36). The horizontal axes
plot percent reactance of carbonate anions (HC03+C03) and non-
carbonate anions (S04+Cl), with each axis reciprocating the
scale of the opposite axis. This diagram provides a method for
"segregating analytic data for critical study with respect to
sources of the dissolved constituents in waters, modifications
in the character of a water as it passes through an area and
related geochemical problems" (Piper, 1944). It allows for
investigation of compositional relations among samples and
statistical populations of samples in the form of clusters of
points.
Salinity sections (Figs. 2.37 and 2.38) can be drawn at any
orientation on the Langelier-Ludwig diagram to depict changes in
concentration. These sections are constructed by projecting all
the data points desired to be included in the section onto a
straight line extending from one L-L diagram axis to an opposite
axis. A triangle is formed by extending two lines from above at
an angle of about 90° to intersect the ends of the L-L diagram
section line. This section can be visualized as one side of a
four-sided pyramid with the L-L diagram as the base (Fig. 2.35).
The apex of the pyramid would represent zero salinity. Lines of
constant chemical constituent ratio and decreasing salinity
would connect points on the L-L diagram, at the pyramid base, to
the pyramid's apex. Then an appropriate milliequivalents per
liter scale is chosen as planes parallel to the base of the
pyramid. The data point is plotted on the salinity section
114
-------
100
PERCENT" REACTANCE
S04+ Cl
MID-LINES
OF SECTIONS
SURFACE OF '
LANGELIER-
LUDWIG
DIAGRAM
\ SURFACES OF
SALINITY
SECTIONS
PERCENT REACTANCE
Figure 2.35 Three-dimensional perspective of a Langelier-Ludwig
diagram showing surfaces of salinity sections.
115
-------
S04 + CI (Percent Reactance)
1C
)0
£%
] 291
Kftfl
afo
e.o
iol
ei i
*"""•
O
a
"o
s
a:
_j —
c
0)
o
a3
Q_
^
_i_
T^
o
^~
n
)0 50 <
OsS A 'B JSjlO Tf 2^l» 7 404,227
• »5 3Sf B38E B248
' ^206 B380
»' BI77
^1^60 ^384
^59 B 36
73 79
• • .367
a38i
• 604IDI
B96 133 134 376
n a •
• • •
I8I2IS)
^^COLOftADO RIVER WATER
BI44
"
^
1> ^
S
-------
100
SECTION A-B
0 SURFACE WATERS
•E GEOTHERMAL FLUID - KGRA CODE
& INTERMEDIATE SAMPLE
a SHALLOW SAMPLE
Na + K ( Percent Reactance )
Na + K (Percent Reactance)
Figure 2.37 Salinity section A-B from Langelier-Ludwig diagram
for groundwater data in Imperial Valley, California,
117
-------
'100
SECTION A-C
0 COLORADO RIVER WATER
if OEOTHERMAL FLUID -KGRA CODE
a INTERMEDIATE SAMPLE
0 SHALLOW SAMPLE
D CLUSTER OF TEN
SHALLOW SAMPLE
No+ K [Percent Reactance)
20
HC03+ C03 (Percent Reactance)
35
100
SECTION A-D
if GEOTHERMAL FLUID - KGRA CODE
c. INTERMEDIATE SAMPLE
A CLUSTER OF TEN
INTERMEDIATE SAMPLES
a SHALLOW SAMPLE
50
SO« + CI (Percent Reactance)
Figure 2.38 Salinity sections A-C and A-D from Langelier-Ludwig
diagram for groundwater data in Imperial Valley,
California.
118
-------
where the salinity value plane intersects the chemical constitu-
ent ratio line. Similar to the L-L diagram, the salinity sec-
tions also allow for investigation of compositional relations
and statistical populations of samples.
Single Chemical Parameter Plots—Three-dimensional surface
plots of single chemical parameter contours (Figs. 2.40 to 2.44)
were used as an additional technique for possible correlation of
ground water chemistry with aquifers, geologic structure or
geothermal anomalies. Since a good portion of the ground water
quality data was already digitized, and computer contouring and
surface drawing routines were available, the capability to do
computer contouring and plotting of specific chemical parameters
existed. This technique could eventually allow generation of
many vertical and horizontal cross sections and surfaces, as
well as trials with different depth interval categories, with
minimal effort and cost. The essence of the idea is to define
the extremely complicated, contorted subsurface structure and
lithology of Imperial Valley, as well as changes in chemical
parameters in the ground water system, that would be shown in
the appropriate combination of contoured cross sections and
three-dimensional surface plots of these contoured cross
sections.
Contoured surfaces for some chemical parameters are illus-
trated in this report and one can delineate specific structural
trends and anomalies on them. It is anticipated that further
interpretation and data manipulation will be possible in later
phases of this study.
Guide to Changes in Water Characteristics—
To aid in tracing the possible genesis of a ground water in
Imperial Valley, chemical reactions that could alter Colorado
River source water were defined and considered (Olmsted, et al.,
1973). In this approach recent Colorado River water is assumed
to undergo certain common geochemical reactions in combination
with various degrees of evaporative concentration. The results
of these reactions are computed, providing a set of known chemi-
cal causes and effects on Colorado River water. By comparing
these known changes with analyses of actual waters, it is pos-
sible to get a suggestion of the processes the water has under-
gone in the ground. A sample of some of these changes, as shown
by modified Stiff patterns, is presented in Figure 2.39. Since
many people may be accustomed to seeing Stiff patterns plotted
in mi Hi equivalents per liter, this figure also compares modi-
fied Stiff patterns plotted in percent reactance with those in
plotted milliequiyalents per liter to illustrate the character-
istics of these different representations.
The first chemical change shown, that of simple evapora-
tion, shows the percent reactance modified Stiff pattern remain-
ing the same size and shape with increasing concentrations due
119
-------
EXPLANATION
IX 2X 3X
CONCENTRATION BY EVAPORATION
730
COLORADO
RIVER
IX
4X
1460 2920
EVAPORATED a SOFTENED
io^iy
1450
MODIFIED STIFF DIAGRAMS PLOTTED IN MILLI EQUIVALENT PER
LITER AND PERCENT REACTANCE FOR COMPARISON OF
CORRESPONDING PATTERN CHANGES
MILLIEQUIVALENTS
PER LITER
."jrfS.
PERCENT REACTANCE
Co HCOj
\
Cl
20IO
/
SUM OF DISSOLVED SOLIDS. IN MILLIGRAMS PER LITER
1260
1140
1130
1110
2X
2920
EVAPORATED 8 PRECIPITATED
5X
8X
IOX
2060 3230
EVAPORATED, PRECIPITATED, 25% SULFATE REDUCTION
1910 3040
EVAPORATED, PRECIPITATED, 40 % SULFATE REDUCTION
3570
,570
Z900
1570 2350
SAME AS ABOVE, PLUS HARDENING EQUAL TO NET INCREASE IN SULFATE
2900
^\
2320
I556"1 2320
SAME AS ABOVE, EXCEPT HARDENING UNTIL CI=Na IN MILLIEQUIVALENTS PER LITER
1520
4X
2250
8X
2690
A
2600
IOX
Figure 2.39 Modified Stiff diagrams representing hypothetical analyses
of groundwater resulting from specified chemical changes
in Colorado River water. (modified from Olmsted, et al., 1973)
-------
to evaporation (Fig. 2.39). The modified Stiff pattern plotted
in milliequivalents per liter maintains a similar shape but
elongates markedly with increasing concentration due to
evaporation.
Other chemical changes that may be expected in groundwater
in this area are softening, carbonate precipitation, sulfate
reduction, hardening, re-solution of precipitated salts, oxida-
tion of dissolved organic substances and mixing of waters of
different chemical composition (Olmsted, et al., 1973). The last
three processes would be difficult to represent and calculate
meaningfully/so they are not presented in Figure 2.39, as are the
other five.
Softening is the replacement of calcium or magnesium, the
hardness-causing constituents, by sodium. This generally occurs
by cation exchange with clay minerals. This change is illus-
trated in the second line of diagrams in Figure 2.39.
Carbonate precipitation occurs when water with high bicar-
bonate and calcium or magnesium content is sufficiently evapo-
rated, resulting in concentration and precipitation of calcium
or magnesium bicarbonate. To distinguish between loss of cal-
cium and magnesium from softening and loss from carbonate pre-
cipitation, one can look for a reduction in bicarbonate, which
occurs with carbonate precipitation but not with softening.
This process is labeled "evaporated and precipitated" on the
third line of diagrams in Figure 2.39.
Sulfate reduction is believed to be a major process occur-
ring in Yuma area groundwater (Olmsted, et al./ 1973), an area
very similar to Imperial Valley. Exactly how sulfate reduction
occurs is poorly understood but it is known to be an organic
process. The last four lines of diagrams in Figure 2.39 involve
sulfate reduction.
Hardening, the reverse of softening, is a base-exchange
process where sodium is replaced by calcium or magnesium. Like
softening, however, hardening is the result of reactions with
clay minerals. The last two lines of diagrams in Figure 2.39
involve hardening.
One conclusion that may be drawn by comparing the different
chemical reactions shown in Figure 2.39 is that the TDS content is
a poor measure of the amount of evaporative concentration of the
sample. The chemical reactions the sample has undergone also
significantly influence the TDS. This can be seen in Fig. 2.39
by comparing the 2,920 mg/1 TDS content of the 4X "concentration
by evaporation" example with the 2,900 mg/1 TDS content of the
10X concentration by "evaporated, precipitated, 40% sulfate
reduction" example.
121
-------
2.5.1 Types and Distribution of Groundwater
The classification, analysis and discussion presented is
mainly descriptive, and it is felt that the charts prepared for
this report will serve as a vehicle for future analysis and
interpretation. Investigators with different backgrounds,
hypotheses and knowledge of Imperial Valley may see different
relations and correlations from the same basic representation of
data. For example, detailed statistical or computer plots of
^additional parameters and sections may prove extremely revealing
and useful. At the very least, the data presented here will
serve as an adequate reference for baseline geochemical rela-
tionships, which will be elaborated in subsequent reports.
One limitation of the data used in this report regards the
areal and vertical distribution of samples (Plate 2.3). Since
the great majority of wells in the valley were drilled for
water, their objective was to find the best producing layer at
the shallowest depth. This objective leads to a very biased
sample. That is, we will have samples from the shallowest, best
producing aquifers. This means that there will be no wells in
areas that are less populated, or less useful, or where usable
water is too deep to be economically extracted. Samples in
areas that are drilled will mostly have representation in the
first good producing aquifer they penetrate, with all aquifers
below not being represented. This situation is illustrated by
comparing the areal distribution of wells in the shallow and
intermediate depth zones (Plate 2.3). The intermediate depth
zone has samples mainly from the artesian aquifer beneath the
area between the East Highline Canal and the Alamo River, while
many samples from the shallow depth zone occur around this area.
Any well drilled between the East Highline Canal and the Alamo
River will most likely penetrate the artesian aquifer while any
well outside of this area will be perforated above the depth of
the intermediate zone, and we get no information about the water
below the shallow depth zone in these areas.
Our sample was additionally limited by the lack of per-
forated interval data for the majority of wells for which we had
chemical data. This resulted in a great concentration of well
samples in an area east of the Alamo River to the southeastern
Imperial Valley and a lower sample density in the western and
southwestern portions of the valley. Northwestern Imperial
Valley, the West Mesa area, the area east of the Coachella Canal
(except for the southeastern part of the valley) and the area
east of the Salton Sea are essentially unrepresented in our
sample.
The following discussion on the types and distribution of
groundwater in Imperial Valley is largely based on the repre-
sentations of groundwater characteristics shown in the modified
Stiff diagrams for the shallow, intermediate and deep depth
zones (Plates 2.4, 2.6 and 2.8). Frequent reference to these
122
-------
plates and to Figure 2.34, showing modified Stiff diagrams for
typical waters, will aid in the following discussion.
Identification and Classification of Characteristic Waters--
"ModifiedStiffdiagramsplotted for the shallow,inter-
mediate and deep depth intervals show the distribution of five
distinct water types in Imperial Valley: a sodium chloride
water, a sodium chloride with high sulfate and/or magnesium
water, a sodium chloride with high calcium water, a high sulfate
water and a sodium bicarbonate water (Fig. 2.34). Definition of
these categories was largely based on distinguishable changes in
the shape of the modified Stiff diagrams. since the modified
Stiff diagrams are plotted in percent reactance, this means that
this classification is based solely on the proportion of ionic
constituents to each other and not at all on the concentration
of the solution. This is a very important factor to keep in
mind for the following discussion.
Points are plotted for all the sample wells on one
Langelier-Ludwig diagram (Fig. 2.36) and three accompanying
salinity cross sections (Figs. 2.37 and 2.38). Points from the
three different depth zones are plotted with three different
symbols to enable possible correlation of composition with
depth. Classifications derived from these plots would be dif-
ferent from those derived from the modified Stiff diagrams
because of the way the anions and cations are grouped in the
plot. It was anticipated that distinctive clusters of points
would represent distinctive groups of origin waters or mixing
paths on the L-L diagram and salinity cross sections; and, in
fact, there is a marked correlation between depth interval and
sample composition. Although there is some scatter, a definite
concentration of shallow interval samples occurs in a zone with
greater than 90 percent reactance (SO^+Cl) and between approxi-
mately 55 and 85 percent reactance (Na+K) (Fig. 2.36). A dis-
tinct concentration of intermediate depth samples occurs in a
zone with greater than 90 percent reactance (Na+K) and between
approximately 25 to 95 percent reactance (S04+C1). Distinct
clusters in this zone occur between 25 and 30 ami between 40 and
52 percent reactance (SCL+C1).
Most of the geothermal waters plot above 98 percent react-
ance (SO.+C1) or (Na+K) (Fig. 2.36). The Salton Sea wells occur
at 100 percent reactance (SO..+C1) and between 64 and 69 percent
reactance (Na+K). Three or the East Mesa wells plot at 98
percent reactance (Na+K) and between 57 and 87 percent reactance
(S04+C1).
Salinity section A-D (Fig. 2.38) shows a very dense cluster
of points in a triangular pattern. This is suggestive of com-
plete mixing of the three waters having compositions represented
by the apexes of the triangular patterns. The composition of
these waters appears to be a fairly pure water of low salinity,
123
-------
a sodium bicarbonate water having a salinity of approximately 60
meq/1, and a sodium chloride water having a salinity of approxi-
mately 110 meq/1. A line of points for the Salton Sea geo-
thermal wells in section A-B of Figure 2.37 shows a relatively
constant ratio of chemical constituents becoming more and more
concentrated by evaporation.
Sodium Chloride Waters—The three sodium chloride waters
mentioned in the previous section will be described below. The
first water is the simple sodium chloride water which contains a
very high proportion of sodium and chloride and a small percent
reactance of other anions and cations (Fig. 2.34). This water
is typified by sample number 297, 320 or 145 in the shallow
aquifer (Plate 2-4). It will be referred to as the simple
sodium chloride water in the following discussion.
The sodium chloride with high sulfate or magnesium is a
water with a high proportion of sodium and chloride, but this
water also contains appreciable amounts of sulfate or magnesium,
generally about 20 to 30 percent reactance, and significantly
lesser amounts of calcium and bicarbonate (Fig. 2.34). Salton
Sea surface waters are typical of this water type. This water
will be referred to as the NaCl-S04~Mg water in the following
discussion.
The sodium chloride water with high calcium also has a very
high proportion of sodium and chloride to the other anions and
cations, but the amount of calcium is noticeably larger than the
percent reactance of any other remaining ion (Fig. 2.34). This
water would be typified by samples in the Salton Sea geothermal
area (Plate 2.8). This water will be referred to as the NaCl-Ca
water in the following discussion.
The simple sodium chloride water occurs in all three depth
zones, but there is a statistically significant correlation of
this water with the shallow depth zone (Plate 2.4). Water of
this type is fairly well distributed throughout the area east of
the New River within the shallow depth zone. The sodium chlo-
ride water occurs very sparsely in the intermediate and deep
aquifers (Plates 2.6 and 2.8).
The NaCl-SO.-Mg water is present in only the shallow and
intermediate depth zones for our sample. In the shallow zone it
occurs near inlets in the southern portion of the Salton Sea and
is typical of Salton Sea water. Similar type waters with high
sodium chloride and notable sulfate occur in the shallow and
intermediate depth zones in southeastern Imperial Valley. A few
samples of other similar waters of this type in the shallow
depth zone occur to the west and northwest of El Centre. A few
more samples of this type occur in the northernmost area of the
intermediate depth zone samples.
124
-------
The NaCl-Ca water only occurs in the deep aquifer and shows
a statistically significant correlation with this aquifer. It
occurs in the Cerro Prieto, Heber and Salton Sea geothermal
fields and there appears to be a distinct north-south trend
between these occurrences. It is possible that there may be
some conduit providing a hydraulic connection between these
waters or they may all be undergoing a similar chemical
reaction.
It is possible that the distinctions between these three
sodium chloride waters may obscure more general ground water
relations. Simpler distribution patterns may possibly be recog-
nized if all the sodium chloride waters were considered as one
group.
Sulfate Water—The high sulfate waters are typified by
average Colorado River water (Plate 2.4; Fig. 2.34). This water
has higher percent reactance sulfate than any other anion, often
50 percent reactance or greater. Most of these waters have
calcium and sodium percent reactance greater than magnesium with
the calcium and sodium often greater than 30 percent reactance
each. This water occurs mainly in the shallow aquifer (Plate
2.4) and has a statistically significant correlation with it.
It occurs mainly beneath and very close to canals in the south-
eastern portion of Imperial Valley, obviously due to leakage of
Colorado River water from the canals. One sample of this water
occurs in the intermediate depth zone directly beneath the
Ail-American Canal and one occurs in the deep depth zone, in the
Dunes geothermal field, just to the northwest of the Coachella
Canal.
Sodium Bicarbonate Waters—The sodium bicarbonate waters in
ImperialValleyhavehigher percent reactance of sodium and
bicarbonate than any other ion (Fig. 2.34). Most of these
waters also have significant chloride. Although samples of this
water occur in all three depth zones there is a marked statis-
tically significant correlation of this type of water with the
intermediate depth zone (Plate 2.6). Almost 80% of the samples
of this type of water occur in the intermediate depth zone.
This is largely confined to the artesian aquifer area, between
the Alamo River and the East Highline Canal. Four of the sam-
ples of this water type occurring in the shallow depth zone are
located just west of the Elsinore Fault trace in the south-
western corner of Imperial Valley. These waters have the lowest
salinities of all our samples, even lower than Colorado River
water. A sample in the intermediate depth zone, located di-
rectly below these four samples, has exactly the same chemical
characteristics. Another sample of this water type in the
shallow aquifer occurs in the southern part of the East Mesa
area, areally to the southeast of this water's occurrence in the
intermediate depth zone. In the deep depth zone, these waters
occur in the East Mesa KGRA and about 6.4 km (4 mi) to the
southeast of Holtville.
125
-------
Discussion of Characteristic Waters by Depth Zone—
ModifiedStiffdiagramsfortheshallow depth interval
(Plate 2-4) show the occurrence of four of the characteristic
water types. The sodium chloride water occurs throughout the
southeastern Imperial Valley, approximately up to the New River.
The high sulfate water appears to be characteristically Colorado
River water and occurs in southeastern Imperial Valley, but is
generally restricted to the Coachella and Ail-American Canal
areas. This would lead one to believe that the Colorado River
.water reacts quite quickly with the sediments and changes char-
acter, picking up significant amounts of sodium and chloride
with very small flow distances in the ground. Salton Sea water
is included in the NaCl-S04-Mg groundwater group. It also
occurs near inlets to the Salton Sea and in an area up to 24 km
(15 mi) west-northwest of El Centre. The sodium bicarbonate
water in the shallow depth interval mainly occurs in four wells
in the extreme southwest corner of the valley.
Most wells in the intermediate zone (Plate 2.6) tap the
artesian aquifer beneath the area between the Alamo River and
the East Highline Canal. The sodium bicarbonate water is very
typical of the intermediate depth interval. Other waters occur-
ring in the intermediate depth zone are a few sporadic simple
sodium chloride waters and some NaCl-SO^-Mg water in the Dunes
geothermal area and in the north part 01 East Mesa; one inter-
mediate depth high sulfate water also occurs under the Ail-
American Canal.
In the deep geothermal depth interval (Plate 2.8), the
NaCl-SO.-Ca water is characteristic of the Salton Sea, Heber and
Cerro Plrieto geothermal fields. However, the concentration of
the fluids of the Salton Sea field is about ten to twenty times
that of Heber and Cerro Prieto. The sodium bicarbonate water
occurs in the deeper zones just west of East Mesa. East Mesa
has a sodium chloride water with some samples high in bicarbo-
nate. An oil test well about 10 km (6 mi) southeast of Brawley
has a sodium chloride water at 4,097 m (13,442 ft) depth con-
taining 52,852 mg/1 TDS. A sample from the Dunes geothermal
field shows the high sulfate water characteristic of the
Colorado River.
Four analyses are available for deep well No. 316 at depths
from 834 to 3,752 m (2,737 to 12,310 ft). These analyses show a
change in the character of the water with depth, from essen-
tially a simple sodium chloride water at around 850 m (2,800 ft)
gradually developing into a sodium bicarbonate water at about
3,700 m (12,000 ft). Also, TDS content increases fairly
linearly from 850 m (2,800 ft) to 3,400 m (11,200 ft) with
salinity going from 3,227 to 8,843 mg/1. But, between 3,400 m
(11,200 ft) and 3,700 m (12,000 ft) a marked discontinuity
occurs in the linear salinity increase and TDS increase from
8,843 to 18,215 mg/1 in the 143 m (470 ft) between these two
126
-------
sample intervals. This marked increase suggests some kind of
impermeable boundary, or perhaps fault, separating these inter-
vals. A more saline zone is also noted in the 1,202 to 1,227 m
(3,945 to 4,026 ft) depth interval in well No. 304 where a TDS
content of 19,000 mg/1 is bounded above by a 13,000 mg/1 water
and below by a 11,800 mg/1 water.
Changes in Water Characteristics With Time—
An attempt was made to delineate changes of water charac-
teristics with time. Unfortunately data distribution with
location and time was not adequate for a detailed analysis of
these chemical changes. Regular or consistent patterns were not
observed; however, observations that were noted are discussed
below.
Eighteen sample wells had complete chemical analyses over
periods of 1 to 19 years. Six of these analyses were over
only one-or two-year periods. Some wells showed changes and
others did not. Well Nos. 60, 230, 253, 364, 381, 384, 420,
713, 714, 720, 738, 742 and 743 (Plate 2.3) exhibit very little
or no significant changes in water character or concentration
over sample intervals which run from 1 to 11 years. These
shallow and intermediate depth samples are areally distributed
throughout the valley ,and the composition of these waters varies
from very low salinity sodium bicarbonate water to sodium chlo-
ride sulfate waters with over 2,760 mg/1 TDS.
Well No. 10 (Plate 2.4), near the Coachella Canal, to the
north of Imperial Valley, has the most complete set of analyses
with time. There are ten analyses for the 19-year period
between 1948 and 1967. The character of this sodium chloride
water with notable carbonate, sulfate and calcium remains basi-
cally the same throughout the analysis period. The TDS content
decreases from 3,850 mg/1 in 1948 to 3,000 mg/1 in the 1962
sample, then starts increasing to 3,475 mg/1 for the most recent
sample which was taken in 1967.
The 1962 and 1970 analyses of well No. 160 (Plate 2.6),
penetrating the intermediate depth artesian aquifer east of the
Alamo River, are quite similar. Both are sodium bicarbonate
waters with very high chloride content. There was an increase
in TDS from 1,640 mg/1 in 1962 to 1,780 mg/1 in 1970 and a small
increase in sulfate. Marked increases in TDS, to 3/910 mg/1, and
in sulfate, from 250 to 450 mg/1, appeared in an analysis done
in 1963. Almost three-quarters of the 270 mg/1 increase in the
TDS content is attributed to the increased sulfate. If this
analysis between 1962 and 1970 were not available, the increase
in sulfate would never have been known in this location. .This
serves as an example of one of the problems involved in deciding
on sample intervals when developing a monitoring methodology.
127
-------
There are three complete analyses available for well No.
248 (Plate 2.4), in the southwestern Imperial Valley, just
southwest of the Elsinore Fault trace. These analyses took
place in 1959, 1962 and 1972. Basically, the water is very low
in TDS, on the order of a few hundred milligrams per liter, but
a noticeable change in the character of the water occurred
between 1959 and 1962, when it changed from a sodium magnesium
bicarbonate chloride water to a sodium bicarbonate chloride
water. That is, a marked reduction in magnesium, from 67 to
3.2 mg/1, occurred in this period. In the period from 1962 to
1972 there was a significant increase in sulfate, from 25 to
46 mg/1, and TDS from 262 to 390 mg/1.
Well No. 393, a shallow well in the extreme southwestern
Imperial Valley (Plate 2.4), shows a change in character in
between the end points of a sample period, as did well No. 160.
The samples for 1967 and November 1972 are quite similar sodium
carbonate chloride waters with a somewhat smaller calcium con-
tent in November 1972 than in 1967. The TDS content was 360
mg/1 in 1967 and 341 mg/1 in November 1972. However, a sample
taken in July 1972 exhibits distinctly higher sulfate and a TDS
content of 455 mg/1. This example again points out the neces-
sity to remain aware of possible undetected changes in water
characteristics between sampling periods.
Well No. 731, in the intermediate depth artesian aquifer
west of the East Highline Canal (Plate 2.6), shows a slight
reduction in TDS, from 2,510 mg/1 in 1961 to 2,440 mg/1 in 1970,
accompanied by an increase in sulfate from 88 to 130 mg/1.
2.5.2 Single-Chemical Parameter Contoured Surface Plots
The areal distribution of the concentration of five repre-
sentative chemical parameters is schematically shown by the
three-dimensional surfaces plotted on Figures 2.40 through 2.44.
The five chemical parameters contoured in this manner are spe-
cific conductance, sulfate, bicarbonate, chloride and calcium.
Interpretation and comparison of the patterns of each of these
surfaces will aid in determination of chemical and/or structural
trends, areas of high correlation between parameters and areas
of low or no correlation between others.
This technique depicts the areal variation of the con-
centration of any single parameter or combination of parameters.
This is accomplished by inputting into the computer the para-
meter values and their corresponding geographic coordinates.
Computer routines then generate a contour map of these values.
Once the contour map is completed another routine generates an
"orthogonal projection" of the contour map, resulting in the
three-dimensional perspective of the contoured surface.
128
-------
-14,000 micromhos
Contour interval
= 1000 micromhos
Figure 2.40 Schematic surface of specific conductance
values in Imperial Valley qroundwater .
32.5-
'/V
-------
• 3000 mg I I
Contour interval
= 300 mg/J?
Figure 2.41
Schematic surface of sulfate values
in Imperial Valley groundwater.
-------
Il20mg/j?
"6.
Contour interval = 80 mg /Jt
Figure 2.42 Schematic surface of bicarbonate
values in Imperial Valley
qroundwater.
-------
19,000 mg/i
to
Contour interval = 1000
Figure 2.43 Schematic surface of chloride values
in Imperial Valley groundwater.
-------
2600 mg /f
400mg/j?
Contour interval = 100 mg/j
Figure 2.44 Schematic surface of calcium values
in Imperial Valley groundwater.
-------
Limitations—
These chemical parameter surfaces were plotted using an
available digitized water quality data base and available com-
puter library graphic routines. Limitations in the digitized
data base and limitations in the capabilities of the computer
library graphic routines necessitated certain compromises in the
resulting plots.
The rationale behind this approach was to determine, with
minimum development cost, the feasibility of utilizing this
methodology in hydrologic and water quality studies. These
limitations and compromises are outlined below and should be
kept in mind when perusing the plots.
The structure and content of the data base did not allow
separation of the plotted surfaces by aquifer depth interval
because there was an insufficient number of water quality anal-
yses with the information necessary for this separation. That
is, the minimum areal distribution of data points necessary to
produce a reasonable contour map was not available. Therefore,
the resulting plots represent essentially all perforated depth
intervals except those in our sample which explicitly stated a
perforated depth interval that included a depth less than 24 m
(80 ft) or any well whose depth was less than 24 m (80 ft).
The remaining limitations involve the computer routines.
The available contouring routine requires the input data values
to be arranged in a regular rectangular grid. Since our data
had a somewhat random areal distribution, it was necessary to
generate a surface through the data points with a bicubic spline
subroutine which then overlaid a rectangular grid on this sur-
face. The intersection points of the generated surface and this
rectangular grid were then fed into the contouring program.
This technique resulted in a generalization and averaging of the
original data that could not be monitored or controlled. There-
fore the surface that is contoured and plotted does not pre-
cisely represent the actual input data. Some particularly high
or low values were averaged; a maximum value cutoff had to be
established for some plots so the lesser variations would not be
masked by a very large contour interval; some unrepresentative
wells received undue emphasis; and so on. Therefore these
surfaces are currently only a schematic representation of the
true data and actual values cannot be read from the plots.
Despite these difficulties, the plots demonstrate that they may
potentially be a valuable technique to rapidly appraise chemical
changes and correlations in the ground water system, as well as
geologic and structural relations.
The five chemical parameters shown in Figures 2.40 through
2.44 were chosen largely for demonstration purposes; however,
the modified Stiff diagrams on Plates 2.4, 2.6 and 2.8 were
studied in an attempt to choose parameters that would show some
134
-------
distinguishing areal distributions. It appears that the para-
meters chosen do demonstrate the potential utility of the
technique.
Discussion of the Contoured Surfaces—
A preliminary description of some features of the computer
contoured surfaces follows. Much more information could be
derived from these plots with further study and correlation with
specific geothermal, lithologic and structural locations as well
as with improvements in the graphical techniques.
The schematic surface of specific conductance values in
Imperial Valley ground water (Fig. 2.40) shows an extremely
distinct northerly trending discontinuity going up in a signifi-
cant, sharp rise to the west. Since specific conductance is
proportional to salinity, it is readily apparent from this plot
that there is a distinct high salinity trend running northerly
through the central part of the valley, and it drops off to both
the east and west, albeit more steeply to the east. The drop in
specific conductance near the southwest corner of the plot may
be correlated with the ground water barrier effect of the Elsi-
nore Fault zone separating the very pure water entering the
valley from the Peninsular Range, to the southwest of the fault,
from the more saline central valley waters.
The schematic surface of sulfate values in Imperial Valley
ground water (Fig. 2.41) shows much higher sulfate in the west-
ern side of the valley. The sulfate values on the eastern side
of the valley are surprisingly consistent. This trend is dif-
ferent from what one would expect from looking at the modified
Stiff diagrams, which show the characteristic Colorado River
waters in the southern valley with high percent reactance sul-
fate. Upon further study the sulfate highs on the plot may be
correlated with geothermal fields or other structures.
The schematic surface of bicarbonate values (Fig. 2.42) is
quite erratic, with high peaks distributed throughout the cen-
tral and eastern parts of the valley. A distinct north-south or
northwest-southeast discontinuity appears in the east- central
part of the valley, probably at the boundary of the artesian
aquifer (i.e., at the Alamo River). Values of this discontinuity
rise to the west and then the schematic surface of bicarbonate
values gradually decreases to the west. One very high peak
occurs at the location of the artesian aquifer, which contains
predominantly sodium bicarbonate water.
The schematic surface of chloride values in Imperial Valley
ground water (Fig. 2.43) was expected to have a high correlation
with the schematic specific conductance value surface, but it
correlates very poorly, if at all. The chloride surface shows
one extreme peak in the location of the Salton Sea geothermal
field. Values are generally higher in the western and north-
western parts of the valley.
135
-------
One very interesting correlation is that between the sche-
matic chloride surface and the schematic surface of calcium
values (Fig. 2.44). These two plots are essentially congruous,
despite the fact that the actual concentrations plotted for
chloride are about five to ten times those plotted for calcium.
This illustrates one more potential use of this technique. That
is, one can see the areal distribution of ratios between dif-
ferent ions. For example, if one compiled cross plots and
tables of all data for an area to determine constituent ratios,
the areal distribution of these constituents would not be con-
sidered in the calculation. With plots such as those repre-
sented here one could easily determine which areas have high
correlations between which constituents and which areas do not.
The separate correlation calculation could be made for separate
geographic areas.
A useful adjunct to utilization of this technique would be
accompanying plots of residual surfaces, the residuals being the
difference between the actual data value and the smoothed,
computed surface value at each actual data point. This would
aid in determining which trends are based on field data and
which are more the result of the computer smoothing routines.
2.5.3 Trace Elements in Geothermal Waters
Geothermal waters contain an unusually high concentration
of trace elements compared to meteoric and sea water. Table 2.6
presents trace element analyses of geothermal wells located on
Plate 2.8 and analyses for Salton Sea water and standard ocean
water for comparison. Note the relatively high concentration of
trace elements in Salton Sea geothermal waters as compared to
waters from Heber and Cerro Prieto.
Geothermal waters in most instances cannot be used as a
domestic or irrigation water resource, due to high salinity and
high concentrations of trace elements, especially arsenic,
boron, barium, fluoride, manganese and zinc. These waters also
contain significant quantities of lithium, an element so unusual
in ordinary water that it is used as a tracer in qroundwater
studies (Phelps and Anspaugh, 1976).
Because the trace element concentrations in water from
various geothermal fields and even from individual geothermal
wells in the same field substantially differ, hazards due to
trace element concentrations must be individually evaluated.
A good background discussion of water quality with respect
to potential use appears in the section titled "Relationship of
Quality of Water to Use" in Hem (1970) and in Appendix A,
* Identification Systems and Criteria Used in this , Report," in
California Department of Water Resources (1970). Therefore,
this topic will not be addressed here.
136
-------
TABLE 2.6 TRACE ELEMENT OPPOSITION OF SALTON TROUGH GEOTHERJVPVL WATERS
WELL
NAME
cniiprF
oUUKLt
MAP #
LOCATION
DATE
Ag
A1
Ar
As
B
Ba
Br
Cd
Cs
Co
Cu
CO,
F
Fe
Ge
Hg
Li
Mo
Mn
Ni
NO,
NHj.
POj,
Rb
Si02
Sr
Zn
Zr
H2S
NOWL 1 N
#1
500
Heber
(ppm)
0.4
4.8
0.2
1.6
0.9
6.6
120
0.68
HOLTZ
#1
501
Heber
(ppm)
15
4.1
6
0.5
1.7
15
4
0.9
268
37
0.3
HOLTZ
#2
s*r~mt/\LJ 1 <•• I"
btUNUn 1 Us
502
Heber
(ppm)
12
8
3
0.*!
1.5
5
4.1
0.9
187
42
0.1
C.B. JACKSON
#1
i -if
7o
503
Heber
(ppm)
0.5
4.8
3
0.4
0.9
20
2.8
1.3
267
32
0.4
J.D. JACKSON
#1
504
Heber
(ppm)
18
5.2
3
0.4
0.6
10
3.4
1.9
268
36
0.5
WILSON MESA
#1 6-1
/•nrfcirn ITT
tUSNtK //
800 802
Brawley E. Mesa
6-9-76
(mg/1) (mg/1)
<0.013
0.04
0.26
9.75
0.010
0.06
0.99
0.4 8.8
<0.1
0.002
40
0.005
0.95
0.1
trace
165 40.75
0.02
320
MESA
6-2
803
E. Mesa
10-23-73
(mq/1)
<0.004
0.045
0.002
1.82
3.2
0.06
0.007
4
0.0)
0.02
<0.l
17
0.8
0.6
250
0.17
0.08
-------
TABLE 2.6 (i-orttinued)
WELL
NAME
MAP #
LOCATION
DATE
Ag
Al
Ar
As
B
Ba
Br
Cd
Cs
Co
I-, Cu
w CO,
oo F 2
Fe
Ge
Hg
Li
Mo
Mn
Ni
NO,
MU
PO,
Rb
SiO.
Sr
Zn
Zr
MESA
8-1
804
E. Mesa
6-22-76
(mg/l)
<0.01
0.02
0.053
1.6
trace
0.01
1.6
<0. 1
<0. 1
0.014
1.1
0.005
0.01
<0. 1
0.34
4.95
<0. 1
389
2.1
<0.01
MESA
31-1
805
E. Mesa
6-18-76
(mg/l)
<0.01
0.02
0.025
2.5
0.02
0.02
1.42
<0. 1
<0. ]
0.008
0.6
0.005
0.01
<0. 1
2.45
-------
TABLE 2.6 (continued)
vo
WELL
NAME
SOURCE
MAP #
LOCATION
DATE
Ag
Al
Ar
As
B
Ba
Br
Cd
Cs
Co
Cu
F°2
Fe
Ge
Hg
Li
Mo
Mn
Ni
US3
Rb **
SiO
Sr L
Zn
SINCLAIR 1-A M-5 M-8
#4
TOSNFR '77 nrrn '77
815 505 507 510
Sal ton Sea Cerro Prieto Cerro Prteto Cerro Prieto
7-5-67
(ppm) (mg/1) (mg/1) (mg/1)
10
332 7 9.9 11
25
14
1,148
287
1,025
5
90 220 1,060 942
434
SALTON SEA
DWR '70
HS/11E-21P
(mg/1)
0
9.2
1
<0.005
<0.0005
0.005
3.2
0.01
<0.2
3.2
0.01
.003
14
11
0.062
SEA WATER
GOLDBERG '63
(mg/1)
0.0003
0.01
0.003
4.6
0.03
65
0.00011
0.005
0.005
0.003
1.3
0.01
0 . 00007
0.00003
0.17
0.01
0.002
0.002
0.12
6.4
8
0.01
109
1,270
1,159
-------
2.6 SEISMICITY
Imperial Valley is one of the most seismically active areas
in the United States. Geothermal production and reinjection may
induce seismicity in and around geothermal areas in Imperial
Valley. It is necessary to distinguish between naturally occur-
ring seismicity and induced seismicity to assess this potential
environmental impact. The following section discusses histor-
ical seismicity, microseismicity, seismic risk and the relation
between earthquakes and geothermal activity in Imperial Valley
area in order to define a baseline level of seismicity and
seismic risk.
2.6.1 Historical Seismicity
The Salton Trough in general, and Imperial Valley in par-
ticular, is characterized by a high level of seismic activity
and a large amount of strain release. Richter (1958) reports
that twelve earthquakes of magnitude (M) 6 or greater have
occurred in the Salton Trough since 1900, and nine earthquakes
greater than magnitude 6.7 have occurred since 1850.
Plate 2.10 is an historical seismicity map for earthquakes
reported by the National Oceanic and Atmospheric Administration
(NOAA) Earthquake Data File, through June 1976. (Meyers and von
Hake, 1976). This map shows the geographic distribution of
instrumentally recorded epicenters in Imperial Valley from 1932
to 1975, with a few additional epicenters located from 1927 to
1931. The density of epicenters is much greater in the western
part of the valley, especially along the San Jacinto Fault Zone.
The minimal number of epicenter locations along the San Andreas
Fault Zone in the eastern part of the valley supports the hy-
pothesis of a shift to the west of the locus of energy release
in the San Andreas Fault south of Bombay Beach (see "Salton
Trough Fault Zone" subsection, Section 2.3.3).Until additional sta-
tions were added in 1973, this eastern portion of the map was
near the boundary of coverage for the Cal Tech seismographic
network. Allen, et al., (1965) are confident that this low level
of activity is representative of the actual seismicity of this
eastern area.
Although earthquakes are generally correlated with faults,
this correlation is not apparent in the Imperial Valley seis-
micity map. This scatter in the epicenter locations is probably
due to:
1) inaccurate locations of epicenters, especially earlier
locations,
2) high density of fault traces, many of which have not
been identified yet,
140
-------
3) seismicity at depth, which may not be directly
correlated with surface geology,
4) earthquakes not always occurring on preexisting
breaks, and r
5) the fact that much strain may be released through
fault creep.
A 20-year average of cumulative shear taken from the Penin-
sular Range to the Chocolate Mountains (Whitten, 1956) suggests
that the entire San Andreas Fault System in the Imperial Valley
area is moving right-laterally at an average rate of approxi-
mately 80 mm/yr (3.1 in/yr). The actual movement is by no
means constant but has varied greatly with time (Garfunkel,
1972a) and location in the valley (Scholz and Fitch, 1969).
Earthquakes occurring along the San Andreas Fault System typi-
cally have focal depths of 5 to 8 km (3 to 5 mi), which is
approximately the basement-sediment interface. Events generally
occur on nearly vertical fault planes and are often associated
with Quaternary fault scarps. A limiting depth for hypocenters
in the valley is about 12 to 15 km (8 to 9 mi) because at depths
greater than this the high thermal gradients generate tempera-
tures sufficient to cause the rocks to move plastically in
response to stress; in the geothermal areas of the valley this
limiting depth is about 8 km (5 mi) lower (Johnson and Hadley,
1976).
The Imperial Valley Earthquake of 1940—
In terms of human disturbance the Imperial Valley earth-
quake of May 18, 1940,was the most significant earthquake in the
Salton Trough. Damage caused by the earthquake extended into
Baja California (Mexico), the adjacent Yuma Valley and the
Salton Sea area to the north. The shock had a magnitude of 7.0
(Richter, 1958) and could be felt for a radius of about 180 km
(112 mi). Casualty reports show that nine persons died due to
the earthquake. Damage was estimated at 5 to 6 million dollars,
including loss of crops due to interruption of water services,
and serious damage occurred in towns of the central and southern
Imperial Valley.
The focal depth was shallow and the dominant motion was
right-lateral displacement along the Imperial Fault (Plate 2.2,
Nos. 16 and 16a). Surface faulting could be traced for several
kilometers northwest and southeast of the epicenter but the
character of the traces was variable. Northwestward, the fault
displacement gradually diminished from 1.5 m (4.9 ft) offsets
near El Centre to 150 mm (5.9 in) near Brawley. The fault
trace curved and splayed northwestward until no evidence 01
141
-------
surface faulting could be found north of Brawley. Southeast-
ward, the trace was nearly straight and offsets gradually dimin-
ished until none could be found 25 km (15.5 mi) south of the
border.
2.6.2 Microseismicity
High levels of microearthquake activity are associated with
the Salton Sea, North Brawley and East Mesa geothermal areas
(Combs and Hadley, 1977; Hill, et al., 1975a; Johnson and
Hadley, 1976).
Earthquake Swarms—
Earthquake swarm activity has been documented on several
occasions in the valley; in some cases, swarms occur on the same
faults as major shocks (Hill, et al. 1975b; Sharp, 1976; Johnson
and Hadley, 1977; Combs and Hadley, 1977). A number of swarms
that have occurred since 1969 have been studied carefully and
these studies have yielded a wealth of data on the structure and
tectonics of the area.
Seismic events in Imperial and Mexicali Valleys during
April and May 1969 were recorded after an extensive seismic net
in the Salton Trough region was established by Cal Tech. From
these as well as from previous recordings, and other geological
data, scientists were able to support the "rhomb graben" theory
for the tectonic evolution of the Salton Trough (see Section
2.3.2). The mechanism for local crustal spreading, suggested
from fault plane solutions, involves en-echelon normal and
strike-slip faults trending oblique to the regional transform
faults. Motion along these faults could account for the observed
crustal rifting.
In 1973, operation of the USGS-Cal Tech seismic net com-
menced in the valley. Several swarms were recorded near
Brawley, Salton Buttes and El Centre on the Imperial Fault. This
earthquake data tends to verify earlier observations on regional
seismicity and establishes definite fault traces for the Brawley
and Imperial Faults.
During late January 1975, the Brawley area was the site of
a major earthquake swarm. Analyses of focal depths, temporal
migration and first motions of earthquakes yielded the following
observations:
1) Earthquake focal depths were shallower inside the
Brawley thermal area than outside, probably because
higher subsurface temperatures cause deeply buried
rocks to move plastically in response to stress. Most
earthquakes in this swarm occurred between 4 and 8 km
(2.5 and 5 mi) depths,
142
-------
2) in the Brawley field many earthquakes occurred along
northeastward trending left-lateral and normal faults
(east-northeast faults 17a, on Plate 2.2 for
example).
This left-lateral fault motion is assumed to be responsible
for the observed crustal spreading at Brawley. Some researchers
have included Heber as another region of crustal spreading, but
its position relative to transform fault segments makes this
assertion doubtful. Earthquake activity at Heber is also no-
ticeably less than at North Brawley or Salton Buttes.
Microseismic Monitoring Networks—
In 1973 the USGS, in cooperation with Cal Tech, established
a 16 station telemetered seismograph network in Imperial Valley
to record and interpret earthquakes related to geothermal phe-
nomena (Hill, et al. 1975a). In the Heber area Chevron Oil
Company has established a closely spaced seismic net to gather
information on background seismicity and the relationship the
proposed geothermal production might have on seismic activity.
In conjunction with the LLL Imperial Valley Environmental
Project, the USGS has completed installation, in October 1976,
of six seismometers in the Salton Sea geothermal field region
(Phelps and Anspaugh, 1976). These instruments will be incorpo-
rated with the USGS regional telemetered network.
2.6.3 Seismic Risk
Earthquake - associated damage in Imperial Valley could
result from fault displacement, strong ground motion (shaking),
ground failure or any combination of these effects. The great
majority of earthquake damage is caused by vibratory ground
motion, not surface rupture. Surface rupture often does not
occur. Based on intensity and duration of shaking and near-
surface soil and geologic conditions, vibratory ground motion
often triggers significant ground failure. Man-made structures
can undergo vibration damage and natural landforms can experi-
ence liquefaction, landsliding and settlement.
The extent of this damage would depend on many variables:
earthquake magnitude, epicentral location, depth of focus,
duration of shaking, intensity of shaking, near-surface soil
foundation and geologic conditions, and structural design.
These factors influence the effect of a particular earthquake on
a particular structure.
Fault traces are widespread throughout the valley and even
though earthquakes will occur on faults, these faults may ce
located virtually anywhere in the valley. However, experience
has shown that the intensity of an earthquake is not necessarily
highest at the surface trace of an earthquake-generating fault.
143
-------
Unless a structure is astride an active fault and can be di-
rectly affected by fault displacement, proximity to an active
fault need not be given undue consideration. In most cases,
ground condition and structural design are more influential
parameters in determining damage due to strong ground motion and
ground failure. Important input in evaluating potential damage
due to ground motion and ground failure is the level of historic
seismicity and expected or estimated rock accelerations.
In Figure 2.45, a frequency-magnitude relation (recurrence
curve) is plotted for earthquakes in Imperial Valley during the
period 1932 to 1972. Recurrence curves are useful in estab-
lishing seismic risk. This is a probablistic approach and does
not mean that specific earthquake occurrences or locations can
be predicted. The seismic activity used for constructing the
recurrence curve is representative of the sum of all recorded
earthquakes in the valley.
Maximum Ground Acceleration—
Relationships between maximum acceleration in rock, magni-
tude of earthquake and the distance of the rock site from the
zone of energy release have been proposed by a number of inves-
tigators and summarized by Seed, et al. (1969). This work has
been updated utilizing additional rock acceleration data re-
corded from the San Fernando earthquake of 1971 and new ana-
lytical techniques.
Figure 2.46 shows ranges of maximum rock acceleration as a
function of distance from the causative fault estimated by
Schnabel and Seed (1972). These rock accelerations would gen-
erally be higher for higher magnitude earthquakes. Also, as the
distance from the causative fault increases, the maximum accel-
eration decreases. Figure 2.46 shows, for example, that an earth-
quake of magnitude 5.6 occurring at a distance of 20 km (12.5 m)
from a given structure will most likely generate a rock acceler-
ation of about 0.09 to 0.23 times the acceleration of gravity
(g). This difference in the estimate of maximum acceleration is
due to the effects of different source mechanisms, travel paths,
topography and rock types.
It must be emphasized that a considerable degree of judg-
ment should be exercised in applying these estimates to any
particular site, especially if the site is not on bedrock. Local
site conditions— that is, the type of deposits that lie above
bedrock and beneath a particular site--have a great influence on
the amplification or attenuation of the rock acceleration. It
may be noted that, except for locations very near the causative
fault on earthquakes with magnitude 8 or greater, the maximum
rock accelerations in Figure 2.46 are substantially lower than the
maximum ground accelerations proposed by Housner (1965) (Fig.
2.47), which reflect the amplifying influence of soil deposits.
The acceleration record of the 1940 Imperial Valley earthquake
144
-------
IMPERIAL VALLEY REGION
1932-1971 15,102 KM2
786 EVENTS M > 3.5
b = 0.85
0001
4567
MAGNITUDE
Figure 2.45 Recurrence curve for earthquakes in Imperial
Valley region,1932-72. (Hileman, et al.,1973)
145
-------
0.8
Probable upper bound
4 6 10 20 40 60 100
Distance from Causative Fault - miles
Figure 2.46 Ranges of maximum acceleration in rock.
(Schnabel and Seed, 1972)
0.5
0.4
o
S 0.3
|02
O.I
Maximum acceleration in
Stiff Soil
(Housner,l965)
(Maximum
acceleration
in rock
(Seed,etal. 1968)
10
70
80
20 30 40 50 60
Distance from Causative Paul! -miles ?
Figure 2.47 Comparison of maximum acceleration in rock
and stiff soil deposits for earthquake
magitude 7. (Seed, et al.,1969)
146
-------
showed a maximum acceleration of 0.32 g. This value is in aood
agreement with the maximum anticipated acceleration on soil
deposits shown in Figure 2.47. However, it is possible that if
the El Centro recording station had been located on a rock
outcrop, the maximum recorded acceleration would have been only
about 0.20 g. In addition, Housner (1965) has claimed that the
upper boundary for the maximum acceleration recorded at El
Centro during the May 1940 earthquake is still higher (about
0.50 g). These differences in the motions developed at the
ground surface can be attributed to the modifying influence of
the soil deposits underlying the recording station.
Data presented by Duke and Leeds (1962) shows that the soil
deposits at the recording station at El Centro consist of about
30 m (99 ft) of stiff clay underlain by several hundred meters
of sediments. The maximum accelerations recorded over such
sites would tend to be higher than anticipated for sites on rock
outcrop. Hence, Housner's curve for stiff soil conditions (Fig.
2.47) is more applicable for the El Centro site.
The preceding discussion points out the wide variations in
recorded accelerations that can be caused by local site condi-
tions. Still greater scatter may be caused by other factors,
such as earthquake source mechanisms and seismic wave travel
paths. For this reason, site specific ground acceleration
studies must be completed for each prospective plant site to
determine the actual earthquake risk at that site.
2.6.4 Relation of Earthquakes to Geothermal Activity
Two relationships between earthquakes and geothermal ac-
tivity have been noted. The first one is a correlation of
microearthquake activity and geothermal anomalies which may be
useful in the discovery of geothermal resource areas. The
second is fluid withdrawal, with or without reinjection, which
may trigger local seismic activity.
With respect to the first correlation, high levels of
microearthquake activity are associated with the Salton Sea,
North Brawley and East Mesa geothermal areas (Combs and Hadley,
1977; Hill, et al.,1975a, Johnson and Hadley, 1976). Ward (1972)
suggests that shocks are generally more frequent and of smaller
magnitude in geothermal areas than in other areas of the same
tectonic setting. Faults related to these microearthquakes may
serve as conduits for circulating brines. In fact, faults in
Imperial Valley may be the "plumbing" for some of the geothermal
areas. For example, at the Salton Sea geothermal area it was
observed that carbon dioxide wells began emitting large quanti-
ties of gas just after earthquakes in the 1930's. Also, earth-
quake focal depths are usually shallower in geothermal areas
than in other seismic areas, implying that microearthquakes are
related to geothermal processes.
147
-------
The possibility of triggering earthquakes by geothermal
production and reinjection is of some concern. Although exist-
ing producing fields at The Geysers, California, and Wairakei,
New Zealand, have long been associated with preexisting earth-
quake activity, neither production areas nor the surrounding
communities have been hampered by earthquakes and no associa-
tions have been drawn between geothermal production and earth-
quake activity.
Existing oil field and waste well data have yielded clues
to the effect of fluid injection on triggering earthquakes. Of
the thousands of existing oil field and waste injection wells,
only a few instances of earthquakes triggered by fluid injection
have been cited in the literature. One of them is at the Rocky
Mountain Arsenal waste disposal well near Denver, Colorado, and
another is at the Rangely Oil Field in northwestern Colorado
(Raleigh, et al., 1976). Epicenters of injection-induced earth-
quakes at Rangely are shown in Figure 2.48. The largest event
registered here was a magnitude 6 earthquake. Earthquakes are
inferred to be caused by an increase in pore pressure that
results in shear failure, therefore reducing the normal stress
across fracture surfaces. However, regional tectonics, the
stress field and rock properties in Imperial Valley are differ-
ent from Rangely, so the Rangely experience may not be applied
to Imperial Valley.
Withdrawal of geothermal fluids may alter deep ground water
flow patterns, and perhaps even the surface flow rate. The
effect of these alterations on the tectonic stress regime is
unknown. Any attempt to assess these effects now, and the
effect of fluid reinjection, is speculative. It will require
several years of continuous monitoring activity, superimposed on
the known background seismicity, to understand the possible
withdrawal and reinjection effects.
Two criteria can be considered useful in detecting induced
earthquakes: frequency-magnitude (recurrence) statistic changes
in the area of the geothermal field, and changes in depth and
location of events from pre-production activity (Phelps and
Anspaugh, 1976).
148
-------
HO 12.0
X X
X**
X
EXPLANATION :
===== • INJECTION WELL *
A SEISMOMETER LOCATION
IMPLIED FAULT
X EARTHQUAKE EPICENTER
CONTOURS SHOW DISTRIBUTION OF PORE PRESSURE IN PSI
(THE ORIGINAL RESERVOIR PORE PRESSURE WAS 2,500 PSI).
I 2 (milts)
^^^^^^^^^
2 (kilometers)
0
h
Figure 2.48 Epicenters of injection-induced earthquakes
at Rangely/ Colorado. (Raleigh, et al., 1972)
149
-------
REFERENCES
Allen, C. R., A. Grantz, J. N. Brune, M. M. Clark, R. V. Sharp,
E. W. Theodore, E. W. Wolfe and M. Wyss. The Borrego
Mountain, California Earthquake of 9 April 1968: A Pre-
liminary Report. Bull. Seism. Soc. Am., v. 58, p. 1183-
1186, 1968.
Allen, C. R., P. St. Amand, C. F. Richter and J. M. Nordquist.
Relationship Between Seismicity and Geologic Structure in
the Southern California Region. Bull. Seis. Soc. Am., v.
55, p. 753-787, 1965.
Allen, C. R., M. Wyss, J. M. Brune, A. Grantz and R. E. Wallace.
Displacements on the Imperial, Superstition Hills, and San
Andreas Faults triggered by the Borrego Mountain Earth-
quake. USGS Prof. Paper 787, 207 p., 1972.
Allison, E. C. Geology of Areas Bordering Gulf of California—A
Symposium. Am. Assoc. Pet. Geol. Mem., v. 3, p. 3-29,
1964.
Arnal, R. E. Limnology, Sedimentation, and Microorganisms of
the Salton Sea, California. Bull. Geol. Soc. Am., v. 72, p.
427-478, 1961.
Babcock, E. A. Structural Geology and Geophysics of the Durmid
Area, Imperial Valley, California. Institute of Geophysics
and Planetary Physics, University of California, Riverside,
145 p., November, 1969.
p_. Detection of Active Faulting Using Oblique Infrared
Aerial Photography in the Imperial Valley, California; in
Cooperative Geological-Geophysical-Geochemical Investiga-
tions of Gepthermal Resources in the Imperial Valley Area
of California, R. W. Rex, Principal Investigator, Univer-
sity of California, Riverside, p. 143-150, 1971.
. Geology of the Northeast Margin of the Salton
Trough, Salton Sea, California. Bull. Geol. Soc. Am., v.
35, p. 321-332, March 1974.
150
-------
Berry, F. A. F. Proposed Origin of Subsurface Thermal Brines
Imperial Valley, California (abs.). Bull. Am. Assoc. Pet
Geol., v. 50, No. 3, p. 644-645, 1966.
Biehler, S. Geophysical Study of the Salton Trough of Southern
California. Ph. D. diss., California Institute of Tech-
nology, unpub., 139 p., 1964.
; Gravity Studies in the Imperial Valley; in Cooper-
ative Geological-Geophysical-Geochemical Investigations of
Geothermal Resources in the Imperial Valley Area of Cali-
fornia, R. W. Rex, Principal Investigator, University of
California, Riverside, p. 29-43, 1971.
Biehler, S., R. L. Kovach and C. R. Allen. Geophysical Frame-
work of Northern End of Gulf of California Structural
Province; in Marine Geology of the Gulf of California, Am.
Assoc. Pet. Geol. Mem., v. 3, p. 126-143, 1964.
Bird, D. K. Geology and Geochemistry of the Dunes Hydrothermal
System, Imperial Valley of California- M.S. thesis, Uni-
versity of California, Riverside, unpub., 132 p., 1975.
Black, W. E., J. S. Nelson and J. Combs. Thermal and Electrical
Resistivity Investigations of the Dunes Geothermal Anomaly,
Imperial Valley, California. EOS Trans. Am. Geophys. Un.
54, No. 11, p. 1214, 1973.
Blaney, H. F. Evaporation from and Stabilization of Salton Sea
Water Surface. Trans. Am. Geophys. Union, v. 36, No. 4, p.
633-640, 1955.
Brune, J.N.,and C. R. Allen. A Microearthguake Survey of the
San Andreas Fault System in Southern California. Bull.
Seism. Soc. Am., v. 57, p. 277-296, 1967.
Burchfiel, B. C. , and G. A. Davis. Structural Framework and
Evolution of the Southern Part of the Cordilleran Orogen,
Western United States. Am. J. Sci., v. 272, p. 97-118,
1972.
Bureau of Reclamation. Geothermal Resource Investigations, East
Mesa Test Site, Imperial Valley, California, A Status
Report. U. S. Dept. of the Interior, 64 p., November 1974.
Bushee, J., J. Holden, B. Geyer and G. Gastil. Lead-alpha Dates
for some Basement Rocks of Southwestern California. Bull.
Geol. Soc. Am., v. 74, p. 803-806, 1963.
California Department of Water Resources. Geothermal Wastes and
the Water Resources of the Salton Sea Area. Bull. 143-7,
123 p., 1970.
151
-------
Carnegie Institute of Washington. Yearbook 22. Washington,
D.C., p. 66, 1924.
Christensen, A. D. Part of the Geology of the Coyote Mountain
Area, Imperial County, California. M.A. thesis, University
of California, Los Angeles, unpub., 188 p., 1957.
Combs, J., Heat Flow and Geothermal Resources for the Imperial
Valley; in Cooperative Geological-Geophysical-Geochemical
Investigations of Geothermal Resources in the Imperial
Valley Area of California, R. W. Rex, Principal Investi-
gator, University of California, Riverside, p- 5-28, 1971.
. Thermal Studies; in Cooperative Investigation of
Geothermal Resources in the Imperial Valley and Their
Potential Value for Desalting of Water and Other Purposes,
R. W. Rex, Principal Investigator, University of Cali-
fornia, Riverside, p. B1-B23, 1972.
Combs, J.f and D. Hadley. Microearthguake Investigation of the
Mesa Geothermal Anomaly, Imperial Valley, California.
Geophysics, v. 42, No. 1, p. 17-33, 1977.
Coleman, G. A. A Biological Survey of the Salton Sea. Cal.
Dept. of Fish and Game, v. 15, No. 3, p. 218-227, 1929.
Coplen, T. B. Origin of the Geothermal Waters in the Imperial
Valley of Southern California; in Cooperative Investi-
gations of Geothermal Resources in the Imperial Valley Area
and Their Potential Value for Desalting of Water and Other
Purposes, R. W. Rex, Principal Investigator, University of
California, Riverside, p. E1-E33, 1972.
. Cooperative Geoqhemical Resource Assessment of the
Mesa Geothermal System. Institute of Geophysics and
Planetary Physics, University of California, Riverside,
Final Report to U.S. Department of the Interior, Bureau of
Reclamation, Contract No. 14-06-300-2479, 97 p., 1976.
Coplen, T. B., J. Combs, W. A. Elders, W. R. Robert, G. Burck-
halter and R. Laird. Preliminary Findings of an Investi-
gation of the Dunes Thermal Anomaly, Imperial Valley,
California. Department of Water Resources, State of Cali-
fornia, and the Institute of Geophysics and Planetary
Physics, University of California, Riverside, 48 p., 1973.
Coplen, T. B., P. Kolesar, R. E. Taylor, C. Kendall and C.
Mooser. Investigations of the Dunes Geothermal Anomaly,
Imperial Valley, California, Part IV. Institute of Geo-
physics and Planetary Physics, University of California,
Riverside, 42 p., 1975.
152
-------
Cosner, S., and J. Apps. Lawrence Berkeley Laboratory Brine
Data File. Revision February 3, 1977.
Craig, H. The Isotopic Geochemistry of Water and Carbon in
Geothermal Areas. Proc. Spoleto Conf. on Nuclear Geology;
in Nuclear Geology in Geothermal Areas, ed. E. Tongiorgi,
Consiglio Nazionale delle Ricerche, Pisa, p. 17-35, 1963.
. Isotopic Composition and Origin of the Red Sea and
Salton Sea Geothermal Brines. Science, v. 154 p 1544-
1548, 1966.
Craig, H., G. Boato and D. E. White. Isotopic Geochemistry of
Thermal Waters. Pub. Nat. Acad. Sci. Nat. Res. Counc.
Wash., v. 400, p. 29-38, 1956.
Crowell, J, C., Displacement Along the San Andreas Fault, Cali-
fornia. Geol. Soc. Am. Special Paper 71, 61 p., 1962.
Crowell, J. C. and T. Suzuki. Eocene Stratigraphy and Pale-
ontology, Orocopia Mountains, Southeastern California.
Bull. Geol. Soc. Am., v. 70, p. 581-592, 1959.
Dibblee, T. W. Geology of the Imperial Valley Region, Geology
of Southern California. Cal. Div. of Mines and Geol.,
Bull. 170, Ch. 2, p. 21-28, 1954.
Duke, C.M.,and D. J. Leeds. Site Characteristics of Southern
California Strong-motion Earthquake Stations. Cal. Div. of
Mines and Geol. Special Publication 38, 28 p., 1962.
Durham, J. W., The Marine Cenozoic of Southern California; in
Geology of Southern California, R. H. Jahns, ed., Cal. Div.
of Mines and Geol., Bull. 170, Ch. 3, p. 23-31, 1954.
Durham, J. W. and E. C. Allison. Stratigraphic Position of the
Fish Creek Gypsum at Split Mountain Gorge, Imperial County,
California. Geol. Soc. Am. Special Paper No. 68, 22 p.,
19 . i
Dutcher, L. C., W. F. Hardt and W. R. Moyle, Jr. Preliminary
Appraisal of Ground Water in Storage with Reference to
Geothermal Resources in the Imperial Valley Area. USGS
Circ. 649, 57 p., 1972.
Elders, W. A., and D. K. Bird. Petrological Studies; in Investi-
gations of the Dunes Geothermal Anomaly, Imperial Valley,
California. Institute of Geophysics and Planetary Physics,
University of California, Riverside, California, No. 74-13,
14 p., 1974.
153
-------
Elders, W. A., R. W. Rex, T. Meidav, P. T. Robinson and s.
Biehler. Crustal Spreading in Southern California.
Science, v. 178, p. 15-24, 1972.
Facca, G- The Structure and Behavior of Geothermal Fields; in
Geothermal Energy (Earth Sciences, 12), Paris, The UNESCO
Press, p. 61-72, 1973.
Garfunkel, Z. The Tectonics of the Salton Trough of California;
in Cooperative Investigations of Geothermal Resources in
the Imperial Valley Area and their Potential Value for
Desalting of Water and Other Purposes, R. W. Rex, Principal
Investigator, University of California, Riverside, p.
H1-H33, 1972a.
. The Structure of the Salton Trough in Southern
California; in Cooperative Investigation of Geothermal
Resources in the Imperial Valley Area and Their Potential
Value for Desalting of Water and Other Purposes, R. W. Rex,
Principal Investigator, University of California, River-
side, p. 11-157, 1972b.
Geonomics, Inc. A Report on Some Geotechnical Aspects of the
Environmental Impact of Geothermal Power Generation at
Heber, Imperial Valley, California. Electric Power
Research Institute, Res. Proj. 580, ER-299, Report No. 1,
79 p., 1976.
Goldberg, E. D. Chemistry - the Oceans as a Chemical System; in
Composition of Sea Water, Comparative and Descriptive
Oceanography, Vol. 2 of The Sea, M. N. Hill, New York
Interscience Publishers, p. 3-25, 1963.
Griscom, A. and L. J. P. Muffler. Aeromagnetic Map and Inter-
pretation of the Salton Sea Geothermal Area, California.
USGS Geophys. Inv. Map No. GP-754, 1971.
Harbeck, G. E., Jr. The Effect of Salinity on Evaporation.
USGS Prof. Paper 272-A, p. 1-6, 1955.
Hardt, W. F. and J. J. French. Selected Data on Water Wells,
Geothermal Wells and Oil Tests in Imperial Valley, Cali-
fornia. USGS Water Resources Division, Menlo Park, Open
File Report, 1976.
Hays, W. H. Geology of the Central Mecca Hills, Riverside
County, California. Ph. D. diss., Yale University, unpub.,
324 p., 1957.
Helgeson, H. C. Geologic and Thermodynamic Characteristics of
the Salton Sea Geothermal System. Am. J. Sci., v. 266, p.
129-166, 1968.
154
-------
Hely, A. G., and E. L. Peck. Precipitation, Runoff and Water
Loss in the Lower Colorado River-Salton Sea Area. USGS
Prof. Paper 486-B, 16 p., 1964.
Hely, A. G., G. H. Hughes and B. Irelan. Hydrologic Regimen of
the Salton Sea. USGS Prof. Paper 486-C, 32 p., 1966.
Hem, J. D. Study and Interpretation of the Chemical Character-
istics of Natural Water. USGS Water Supply Paper 1473, 363
p., 1970.
Hileman, J. A., C. R. Allen and J. M. Nordquist. Seismicity of
the Southern California Region, 1 January, 1932 to 31
December, 1972. Bull. Seis. Lab., California Institute of
Technology, Pasadena, California, 1973.
Hill, D. P., P. Mowinckel and K. M. Lahr. Catalog of Earth-
quakes in the Imperial Valley, California, June 1973 to May
1974. USGS, Menlo Park, California, Open File Report No.
75-101, 25 p., 1975a.
Hill, D. P., P. Mowinckel and L. G. Peake. Earthquakes, Active
Faults, and Geothermal Areas in the Imperial Valley, Cali-
fornia. Science, v. 188, p. 1306-1308, 1975b.
Housner, G. W. Intensity of Earthquake Ground Shaking near the
Causative Fault. Proceedings, Third World Conference on
Earthquake Engineering, New Zealand, v. 1, 1965.
Howard, C. S. Quality of Water of Colorado River, 1925-1940.
USGS Open File Report, 103 p., 1955.
Irelan, B. Salinity of Surface Water in the Lower Colorado
River-Salton Sea Area. USGS Prof. Paper 486-E, 39 p.,
1971.
Jahns, R. H. Investigations and Problems of Southern California
Geology. Cal. Div. of Mines and Geol., Bull. 170, Ch. 1,
p. 5-29, 1954.
Jennings, C. W. Geological Map of California, Salton Sea Sheet.
Calif. Div. Mines and Geol., 1967.
Fault Map of California. Cal. Div. Mines and
Geol., Calif. Geol. Data Map Series, Map No. 1, Faults,
Volcanoes, Thermal Springs, and Wells, 1975.
Johnson, C. E./ and D. M. Hadley. Tectonic Implications of the
Brawley Earthquake Swarm, Imperial Valley, California.
Bull. Seis. Soc. Am., v. 66, No. 4, p. 1133-1144, 1976.
155
-------
Kelley, V. C.,and J. L. Soske. Origin of the Salton Volcanic
Domes, Salton Sea, California. J. Geol., v. 44, p. 496-
509, 1936.
Kohler, M. A., T. J. Nordenson and D. R. Baker. Evaporation
Maps for the United States. U. S. Weather Bur. Tech. Paper
37, 13 p., 1959.
Kovach, R. L., C. R. Allen and F. Press. Geophysical Investi-
gations in the Colorado Delta Region. J. Geophys. Res., v.
67, p. 2847-2871, 1962.
Langelier, W. F., and H. F. Ludwig. Graphical Methods for Indi-
cating the Mineral Character of Natural Waters. J. Am.
Water-Works Assoc., v. 34, p. 335-352, 1942.
Larson, R. L., H. W. Menard and S. M. Smith. Gulf of Cali-
fornia: Result of Ocean Floor Spreading and Transform
Faulting. Science, v. 161, p. 781-784, 1968.
La Rue, E. C. Colorado River and Its Utilization. USGS Water
Supply, Paper 395, 231 p., 1916.
Littlefield, W. M. Hydrology and Physiography of the Salton
Sea, California. USGS Hydrol. Inv. Atlas, HA-222, 1966.
Loeltz, O. J., B. Irelan, J. H. Robinson and F. H. Olmsted.
Geohydrologic Reconnaissance of the Imperial Valley, Cali-
fornia. USGS Prof. Paper 486-K, 54 p., 1975.
Lofgren, B. E. Measuring Ground Movement in Geothermal Areas of
Imperial Valley, California. Proc. of Conference on
Research for the Development of Geothermal Energy
Resources, Pasadena, California, p. 128-133, 1974.
Lomnitz, C., F. Moosef, C. R. Allen, J. N. Brune and W.
Thatcher. Seismicity and Tectonics of the Northern Gulf of
California Region, Mexico—Preliminary Results. Institute
Geofisico Internacional Anales, v. 10, No. 2, p. 37-48,
1970.
MacDougal, D. T., et al. The Salton Sea. Carnegie Inst.,
Wash., Pub. 193, 182 p., 1914.
McDonald, C. C., and O. J. Loeltz. Water Resources of Lower
Colorado River-Salton Sea Area as of 1971, Summary Report.
USGS Prof. Paper 486A, 34 p., 1976.
McEldowney, R. C. An Occurrence of Paleozoic Fossils in Baja
California, Mexico. Geol. Soc. Am. Abs. with Program, v.
2, No. 2, p. 117, 1968.
156
-------
Meidav, T. Report on a Marine Seismic Survey, Salton Sea,
Southern Part. Submitted to California Department of Water-
Resources, 1968a. [Also in Geothermal Wastes and the Water
Resources of the Salton Sea Area. Calif. Dept. Water Res
Bull. 143-7, Sacramento, California, 1972.]
. Structural Characteristics of the Salton Sea,
' California (abs.). Trans. Am. Geophys. Un., v. 49, No. 3,
presented at Western National Meeting of the AGU in San
Francisco, December 2-5, 1968.
. Geoelectrical Exploration of a Geothermal Area in
Southern California (abs.). Trans. Am. Geophys. Un., v.
50, No. 4, p. 348, 1969.
Meidav, T., and R. Furgerson. Resistivity Studies of the
Imperial Valley Geothermal Area, California. Geothermics,
v. 1, No. 2, p. 47-62, 1972.
Meidav, T., R. James and S. Sanyal. Utilization of Gravimetric
Data for Estimation of Hydrothermal Reservoir Character-
istics in the East Mesa Field, Imperial Valley, California.
Stanford Geothermal Program Workshop on Geothermal Reser-
voir Engineering and Well Simulation, Stanford University,
1975.
Meidav, H. T./ and R. W. Rex. Investigation of Geothermal Re-
sources in the Imperial Valley and Their Potential Value
for Desalination of Water and Electricity Production.
University of California, Riverside, 54 p., 1970.
Meidav, H. T., and S. Sanyal. A Comparison of Hydrothermal
Reservoirs of the Western United States. Electric Power
Research Institute, Res. Proj. No. 580, 170 p., 1976.
Meidav, H. T., R. West, A. Katzenstein and Y. Rotstein. An
Electrical Survey of the Salton Sea Geothermal Field,
Imperial Valley, California. Lawrence Livermore Laboratory
Res. Proj. No. 8432305, 132 p., 1976.
Meinzer, O. E. Outline of Ground Water Hydrology, with Defini-
tions. USGS Water Supply Paper No. 494, 71 p., 1923.
Mercado, G. S. Localizacion de Zonas de Maxima Actividad Hidro-
termal por Medio de Proporciones Quimicas, Campo Geotermico
Cerro Prieto, Baja California, Mexico. Tercio Cong. Mex.
Quimica, Guadalajara, 32 p., 1968.
Merriam, R.,and 0. L. Bandy. Source of Upper Cenozoic Sediments
in Colorado River Delta Region. Sed. Petrol., v. 35, No.
4, p. 911-916, 1965.
157
-------
Metzger, D. G., O. J. Loeltz and B. Irelan. Geohydrology of the
Parker-Blythe-Cibola Area, Arizona and California. USGS
Prof. Paper, 486-G, 130 p., 1974.
Meyers, H., and C. A. von Hake. Earthquake Data File Summary.
U. S. Department of Commerce, National Oceanic and Atmos-
pheric Administration, Environmental Data Service, National
Geophysical and Solar-Terrestrial Data Center, Boulder,
Colorado, 53 p., 1976.
Miller, W. J. Geology of the Palm Springs-Blythe Strip, River-
side County, California. Calif. J. Mines and Geol., v. 40,
p. 11-72, 1944.
Minch, J. A. The Late Mesozoic-Early Tertiary Framework of
Continental Sedimentation, Northern Peninsular Range, Baja
California, Mexico. Ph. D. diss., University of Cali-
fornia, Riverside, unpub., 192 p., 1972.
Muffler, L. J. P., and B. R. Doe. Composition and Mean Age of
Detritus of the Colorado River Delta in the Salton Trough,
Southeastern California. J. of Sed. Petrol., v. 35, p.
384-399, 1968.
Muffler, L. J. P./ and D. E. White. Active Metamorphism of Upper
Cenozoic Sediments in the Salton Sea Geothermal Field and
Salton Trough, Southeastern California. J. of Sed.
Petrol., v. 35, p. 384-399, 1968s •
\
. Origin of C02 in the Saltori Sea Geothermal Field,
Southeastern California, U.S.A. XXIII International Geol.
Congress, Prague, 1968, v. 17, Symposium II, Proc.,
Genesis of Mineral and Thermal Waters, p. 185-194, 1968b.
Olmsted, F. H., 0. J. Loeltz and B. Irelan. Geohydrology of the
Yuma Area, Arizona and California. USGS Prof. Paper No.
486-H, 227Np., 1973.
Palmer, T. D., J. H. Howard and D- P. Lande. Geothermal De-
velopment of the Salton Trough, California and Mexico.
Lawrence Livermore Laboratory, 45 p., 1975.
Phelps, P. L.,and L. R. Anspaugh. Imperial Valley Environmental
Project: Progress Report. Lawrence Livermore Laboratory,
UCRL-50044-76-1, 214 p., 1976.
Piper, A. M. A Graphic Procedure in the Geochemical Interpre-
tation of Water Analyses. Trans. Am. Geophys. Un., Hydrol-
ogy Papers, p. 914-923, 1944.
158
-------
Raleigh, C. B., J. H. Healy and J. D. Bredehoeft. Faulting and
Crustal Stress at Rangely, Colorado; in Flow and Fracture
of Rocks, Geophys. Monogr. 16, Am. Geophys. Un D 275-
284, 1972. P'
An Experiment in Earthquake Control at Rangeley,
Colorado. Science, v. 191, p. 1230-1236, 1976.
Randall, W. Percent Volume Sand Bodies in the Imperial Valley
(Preliminary Report); in Cooperative Geological-Geophysi-
cal-Geochemical Investigations of Geothermal Resources in
the Imperial Valley Area of California, R. W. Rex, Princi-
pal Investigator, University of California, Riverside, p.
119-124, 1971.
. An Analysis of the Subsurface Structure and Strati-
graphy of the Salton Sea Geothermal Anomaly, Imperial
Valley, California. Ph. D. diss., University of Cali-
fornia, Riverside, unpub., December 1974.
Reed, M. J. Preliminary Report on the Geology and Geochemistry
of the Cerro Prieto Field; in Cooperative Investigations of
Geothermal Resources in the Imperial Valley Area and their
Potential Value for Desalting of Water and Other Purposes,
R. W. Rex, Principal Investigator, University of Cali-
fornia, Riverside, 1972.
. Chemistry of Thermal Water in Selected Geothermal
Areas of California. Calif. Div. Oil and Gas, Report No.
TR15, 1975.
Rex, R. W. Investigation of Geothermal Resources in the
Imperial Valley and Their Potential Value for Desalination
of Water and Electricity Production. University of Cali-
fornia, Riverside, 14 p., 1970.
. Origin of the Salt in the Imperial Valley and
Surrounding Watershed Areas; in Cooperative Investigations
of Geothermal Resources in the Imperial Valley Area and
their Potential Value for Desalting of Water and Other
Purposes, R. W. Rex, Principal Investigator, University of
California, Riverside, Section F, 1972.
Rex, R. W., E. A. Babcock, S. Biehler, J. Combs, T. B. Copen, W.
A. Elders, R. B. Furgerson, Z. Garfunkel, T. Meidav and P.
T. Robinson. Cooperative Geological-Geophysical-Geochemi-
cal Investigations of Geothermal Resources in the Imperial
Valley Area of California, University of California,
Riverside, 153 p., 1971.
159
-------
Rex, R. W., S. Biehler, J. Combs, T. B. Coplen, R. B. Furgerson,
Z. Garfunkel, T. R. Getts, J. P. Maas and M. Reed. Cooper-
ative Investigations of Geothermal Resources in the
Imperial Valley Area and their Potential Value for Desalt-
ing of Water and Other Purposes, University of California,
Riverside, 268 p., 1972.
Rienter, C. F. Elementary Seismology. W. H. Freeman and Com-
pany, Inc., 768 p-, 1958.
Robinson, P. T., and W. A. Elders. Late Cenozoic Volcanism in
the Imperial Valley, California; in Cooperative Geological-
Geophysical-Geochemical Investigations of Geothermal Re-
sources in the Imperial Valley Area of California, R. W.
Rex, Principal Investigator, University of California,
Riverside, p. 151-153, 1971.
Robinson, P. T., W. A. Elders and L. J. P. Muffler. Quaternary
Volcanism in the Salton Sea Geothermal Field, Imperial
Valley, California. Bull. Geol. Soc. Am., v. 87, No. 3, p.
347-360, 1976.
Rogers, T. H. Geologic Map of California, Santa Ana Sheet. Cal.
Div. Mines and Geol., 1965.
Savage, J. C., D. Goodreau and W. H. Prescott. Possible Fault
Slip on the Brawley Fault, Imperial Valley, California.
Bull. Seism. Soc. Am., v. 64, p. 713-715, 1974.
Schnabel, P. B., and H. B. Seed. Accelerations in Rock for
Earthquakes in the Western United States. Earthquake
Engineering Research Center, College of Engineering, Uni-
versity of California, Berkeley, Rept. No. EERC 72-2, 15
p., July 1972.
Scholz, C. H.,and T. J. Fitch. Strain Accumulation Along the
San Andreas Fault. J. Geophys. Res., v. 74, No. 27, 1969.
Seed, H. B., I. M. Idriss and F. W- Kiefer. Characteristics of
Rock Motions During Earthquakes. J. Soil Mech. and Fndns.
Div. ASCE, v. 95, p. 1199-1218, 1969.
Sharp, R. V. San Jacinto Fault Zone in the Peninsular Ranges of
Southern California. Bull. Geol. Soc. Am., v. 78, p.
705-730, 1967.
. The Borrego Mountain Earthquake of April 9, 1968.
Tectonic Setting of the Salton Trough. USGS Prof. Paper
787, p. 3-15, 1972.
f
. Surface Faulting in Imperial Valley During the
Earthquake Swarm of January-February, 1975. Bull. Seism.
Soc. Am., v. 66, No. 4, p. 1145-1154, 1976.
160
-------
Sharp, R. V., and M. M. Clark. Geologic Evidence of Previous
Faulting Near the 1968 Rupture on the Coyote Creek Fault
In The Borrego Mountain Earthquake of April 9 1968 uses
Prof. Paper No. 787, p. 131-140, 1972.
Silver, L. T. Problems of Crystalline Rocks of the Transverse
Ranges. Geol. Soc. Am. Abs. with Program, v. 3 n 193-
194, 1971. , P. o
Stiff, H. A. Jr. The Interpretation of Chemical Water Analysis
by Means of Patterns. J. Pet. Tech., v. 3, No. 10 D
15ff, 1951.
Strand, R. G. Geologic Map of California, San Diego-El Centre
Sheet. Cal. Div. Mines and Geol., 1962.
Suppe, J.,and R. L. Armstrong. K-Ar Reconnaissance of Mesozoic
Basement Rocks of Southern California. Geol. Soc. Am. Abs.
with Program, v. 3, p. 205, 1971.
Sykes, G. The Colorado Delta. Carnegie Inst., Wash., Pub. 460,
193 p., 1937.
Sylvester, A. G., and R. R. Smith. Tectonic Transpression in San
Andreas Fault Zone. Bull. Am. Assoc. Petrol. Geol., v.
1.60, No. 12, p. 2081-2102, 1976.
Tarbet, L. A., and W. H. Holman. Stratigraphy and Micropaleon-
tology of the West Side of Imperial Valley, California
(abs.). Bull. Am. Assoc. of Petrol. Geol., v. 28, p.
1781-1782, 1944-
Van De Kamp, P. C. Holocene Continental Sedimentation in the
Salton Basin, California, A Reconnaissance. Bull. Geol.
Soc. Am., v. 84, p. 827-848, 1973.
Van Winkle, W.,and F. M. Eaton. The Quality of Surface Waters
of California. USGS Water Supply Paper 237, 142 p., 1910.
Ward, P. L. Microearthquakes: Prospecting Tool and Possible
Hazard in the Development of Geothermal Resources. Geo-
thermics, v. 1, No. 1, p. 3-13, 1972.
Whitten, C. A. Crustal Movement in California and Nevada.
Trans. Am. Geophys. Un., v. 37, No. 4, p. 393-398, 1956.
White, D. E. Saline Waters of Sedimentary Rocks; in Fluids in
Subsurface Environments. Am. Assoc. Pet. Geol. Mem. 4, p.
342-366, 1965.
_ . Environments of Generation of Some Base-metal Ore
Deposits. Econ. Geol., v. 63, No. 4, p. 301-335, 1968.
161
-------
. Geochemistry Applied to the Discovery, Evaluation
and Exploitation of Geothermal Energy Resources; in United
Nations Symposium on the Development and Utilization of
Geothermal Resources, Pisa, v. 2, Part I, Geothermics,
Special Issue 2, 1970.
Wilt, M. J. An Electrical Survey of the Dunes Geothermal
Anomaly and Surrounding Region, Imperial Valley, Cali-
fornia. M.S. thesis, University of California, Riverside,
unpub., 128 p., 1975.
Woodard, G. D. Stratigraphic Succession of the West Colorado
Desert, San Diego and Imperial Counties, Southern Cali-
fornia. Geol. Soc. Am. Abs. with Program, Cordilleran
Section, San Diego, California, p. 73-74, 1961.
Woodring, W. P. Distribution and Age of the Marine Tertiary
Deposits of the Colorado Desert. Carnegie Inst., Wash.,
Pub. No. 18, p. 1-25, 1932.
162
-------
SECTION 3
THE GEYSERS
3.1 INTRODUCTION
This section presents baseline data on climatology, geol-
ogy, hydrology and seismology to aid in assessment of envi-
ronmental impacts of gepthermal development in The Geysers
geothermal area, California. Descriptions of aspects of clima-
tology, geothermal characteristics, tectonics, faults, strati-
graphy, lithology and surface water that are related to and
influence the ground water regime are discussed. A comprehen-
sive discussion of seismic risk in general, and The Geysers area
in particular, is included.
3.1.1 Summary
The Geysers geothermal field produces 99% pure steam from
fractured Mesozoic greywacke of the Franciscan Formation. Near
the original fumaroles, wells were drilled to less than 600 m
(2,000 ft), producing from a fractured reservoir at average
shut-in pressures of 14 to 17.5 kg/sq cm (200 to 250 psig), and
with several degrees of superheat. Wells drilled at distances
of up to 11 km (7 mi) from the original site go to depths of
2,100 to 2,700 m (7,000 to 9,000 ft), encountering a reservoir
at about 230°C (446°F), with markedly subhydrostatic pressures
(32 to 35 kg/sq cm [450 to 500 psig]). Approximately 50 sq km
(20 sq mi), capable of sustaining production of at least 2,000
MW, has been proven by drilling.
Steam from The Geysers carries notable quantities of hydro-
gen sulfide, ammonia and boron as part of the average 1% of
noncondensible gases (principally carbon dioxide). Because of
potential pollution problems, all condensed steam is reinjected
into the geothermal reservoir. Evaporated steam liberates hydro-
gen sulfide to the environment.
Elsewhere in the region, ground water anomalies in boron,
ammonia, chloride and magnesium are noted. The wide extent of
these anomalies suggests that additional thermal resources (per-
haps in the form of saline hot water) exist beneath areas north
and northeast of The Geysers field.
163
-------
3.1.2 Background
The Geysers geothermal field is located in Lake and Sonoma
Counties, of the northern Coast Ranges, California, some 130 km
(80 mi) north of San Francisco (Fig. 3.1). Exploration for
geothermal steam began in this area of fumaroles in the 1920s.
However, first commercial production of electricity from the
steam was achieved only in 1960. Exploration has continued over
an ever-widening area in four counties (Lake, Sonoma, Napa and
Mendocino). This has entailed geologic mapping, hydrologic and
hydrochemical surveys , gravimetry, aeromagnetometry, geoelectri-
cal and seismic surveys and the drilling of hundreds of shallow
holes for temperature gradients, by private companies, govern-
ment agencies and institutional researchers. The work has
accelerated greatly since the inception of the Federal Geother-
mal Leasing Program in 1973. Over 120 deep exploratory wells
have been drilled to date. For this study, published and unpub-
lished data files were canvassed and compiled into text, illus-
trations and tables. Additionally, interviews were held with
persons active in exploration or research into the geothermal
system. Finally, field checks were made into areas of inade-
quate or inconsistent data.
Principal published sources include geologic mapping by
Hearn, et al. (1975) and McLaughlin (1974), seismic studies by
Bufe, et al. (1976) and Iyer (1975) and hydrologic surveys by
the California Department of Water Resources (1957) and by Upson
and Kunkel (1955).
3.1.3 Climatology
The Coast Range in this region is subject to a Mediterran-
ean climate, characterized by mild winters and warm summers,
with nearly all precipitation falling as winter rain. Prevail-
ing winds are westerly, with average speeds in the neighborhood
of 16 km/hr (10 mph), being rather faster in summer than winter.
As a consequence of low wind speeds and summer fog which occurs
mainly in the immediate vicinity of the coastline, the tempera-
ture moderating influence of the ocean decreases markedly with
distance from the coast. Therefore, summers become hotter and
winters cooler going east from Healdsburg to Clear Lake. Simi-
larly, diurnal extremes become greater to the east.
Temperature—
Average annual temperature at Healdsburg is nearly 16°C
(60°F) in the Healdsburg-Cloverdale area, and about 14°C (57°F)
at Lakeport. Across the area, representative mean minimum and
maximum temperatures are 2°C (36°F) and 13°C (56°F) in January,
and 12°C (54°F) and 33°C (92°F) in July. At Clear Lake, average
extreme values are more divergent, with a low of 0°C (32°F) in
164
-------
Clear
Lake
I22°00'
I
-39°00'-
The Geysers
Production Area
Lake
Berryessa
Pacific Ocean
SCALE 1: 1,000,000
(kilometers)
0 10 20 30 40
I H r—1—i S—
05 10 15 20 25
( miles)
Figure 3.1 Location map of The Geysers study area.
165
-------
January and high of 36°C (96°F) in July. The freeze-free period
averages approximately 200 days but is only about 150 days at
Clear Lake. Table 3.1 summarizes temperature data for the
region.
Precipitation—
Average annual precipitation ranges from a low of 635 mm
(25 in) at Clear Lake to a maximum of 2,030+ mm (80+ in) at
the Helen Mine, in the Mayacmas Mountains. Practically all
precipitation falls as rain, although in some years a few inches
of snow falls at elevations over about 300 m (1,000 ft). About
95% of rainfall occurs during the months October through April;
rainfall is heaviest from December to February. Precipitation
data is summarized in Table 3.1 and Figure 3.2.
Wind--
Wind data has been collected on Cloverdale Peak and near
The Geysers by Pacific Gas and Electric Company (PG & E)
(Mooney, 1975). The Geysers station is located on a ridge crest
about 3 km (2 mi) north of The Geysers, at an elevation of 974 m
(3,195 ft); Cloverdale Peak station is at an elevation of 891 m
(2,924 ft) and is approximately 31 km (19 mi) northwest of The
Geysers. The data is given in terms of frequency of occurrence
for winds in 16 azimuthal sectors and in 9 speed intervals, for the
period November 1, 1972, to October 31. 1974. It is seen that at Clover-
dale Peak winds are predominantly irom the north at an average
speed of 13 km/hr (8 mph); winds from the south to southwest are
also frequent, at average speeds from 13 to 19 km/hr (8 to 12
mph). Near The Geysers, wind distribution is bimodal, being
most frequent from the north-northeast at 23 km/hr (14 mph) and
southwest at 14 km/hr (9 mph). At both stations southwesterly
winds characterize winterstorm (cyclonic) weather, while north-
erly winds accompany prevailing good weather (anticyclonic)
conditions. Winds rarely have speeds below 6 km/hr (4 mph) or
above 29 km/hr (18 mph); occurrences beyond these limits are
some 15% of the total.
Evaporation and Transpiration—
Pan evaporation averages nearly 1,370 mm (54 in) annually
in the study region, and measurement points have been located at
Geyserville, Knights Valley, Lower Lake and Lakeport. Because
pan evaporation data is not readily interpretable, it is not
detailed here. However, details are available from California
Department of Water Resources Bulletins 73-1 (1974) and 113-3
(1975).
Data on evaporation and transpiration for native vegetation
are very sparse; practically all studies on evapotranspiration
have concerned irrigated crops. However, one detailed study of
evapotranspiration in native vegetation is available. This
concerns a 17.5 ha (43 acre) area located 16 km (10 mi) north-
east of Lincoln, in Placer County, California (Lewis and Burgy,
166
-------
TABLE 3.1 AVERAGE MONTHLY AND ANNUAL TEMPERATURES AND PRECIPITATION
AT SELECTED STATIONSl
STAT 1 ON
HEALDS-
BURG
ST.
HELENA
LAKE-
PORT
(T)
(P)
(T)
(P)
(T)
(P)
JAN.
46.9
8.5
45.8
7.0
242.6
6.1
FEB.
50.4
7.3
49.0
6.3
46.2
MAR.
53.8
52.4
4.3
49.6
3.4
APR.
57.4
2.9
56.7
2.4
52.1
2.0
AVERAGE ANNUAL
MAY
62.3
1.2
61.8
1.0
61.8
0.9
JUNE
67.2
0.5
67.1
0.3
68.9
0.5
TEMPERATURE
JULY
69.4
0
70.7
0
75.7
0.1
AND PREC
AUG.
68.9
0.1
69.7
0.1
74.8
0.1
1 P 1 TAT 1 ON
SEPT.
68.0
0.4
67.5
0.2
68.5
0.2
OCT.
62.1
2.2
60.8
1.7
57.6
1.7
NOV.
53.9
3.9
53.2
3.1
49.2
2.9
DEC.
M^HMMMH
48.3
7.9
47.4
6.6
41.5
5.9
STATION
CLOVERDALE
HEALDSBURG
THE GEYSERS
LAKEPORT
LOWER LAKE
MIDDLETOWN
CALISTOGA
ST. HELENA
HELEN MINE
MT. ST. HELENA
TEMP.
PRECI P.
60.4
59-1
NA
56.93
NA
NA
NA
58.5
NA
NA
40.5
39.8
51.73
28.5
29 5
46. 83
37.83
33.1
88. 0**
60. 5 5
(est imated)
1) Temperature (T) in °F and precipitation (P) in inches. Data source is Water Information Center,
1974, unless otherwise noted in the following footnotes.
2) U.S. Dept. of Interior, 1973.
3) NOAA, 1975 (Climatological Data, Annual Summary).
A) Kunkel and Upson, I960 (Water Supply Paper 1495).
5) Upson and Kunkel, 1955 (Water Supply Paper 1297).
-------
Clear Lake - Geysers
LEGEND
Lines of Mean Annual Precipitation
KGRA Boundary
Figure 3.2 Precipitation in The Geysers-Clear Lake area,
(mean annual, in inches)
168
-------
1961-67); this is in the foothills of the Sierra Nevada Mount-
ains, at an elevation of about 180 m (600 ft) above sea level
Vegetation is chaparral, comprising chiefly buckbrush, poison
oak, several species of oak, and yellow pine. Rainfall there
averages 635 mm (25 in) annually. Comprehensive monitoring of
climatic and hydrologic conditions, including soil moisture and
ground water storage, was carried out during the seven-year
study.
The study showed that evapotranspiration (ET) ranged from
510 to 685 mm (20 to 27 in) per year, depending on rainfall.
Minimum ET (510 mm [20 in ]) occurred when rainfall was 810 mm
(32 in), and maximum ET (685 mm [27 in ]) when rainfall was 865
mm (34 in) ; significant decreases in soil moisture and ground
water storage accompanied the period of minimum rainfall and ET.
It was concluded that, up to a maximum of about 685 mm (27 in) ,
ET used essentially all available rainfall in any given year;
for rainfall greater than 685 mm (27 in ), ET increased only
slightly, to a maximum of 710 mm (28 in).
Vegetation over much of the present study region is some-
what comparable in makeup with that of the Placer County area,
being largely mixed chaparral in nature; however, mixed broad-
leaf woodland (chiefly oak, with madrone, laurel and toyon), and
conifer woodland at higher elevations, are present in the Mayac-
mas Mountains. Because rainfall in the study area is greater
than in the reference area, it can be reasonably assumed that
the established plant community has a minimum ET equal to or
greater than that of the reference area, i.e., some 560 mm (22
in) annually. More specifically, it is reasonable to assume
that: (1) the Mayacmas Mountains area has ET near or perhaps
greater than the maximum ET observed in the reference area, (2)
the drier, scrubbier area to the east has ET very close to that
of the reference area. On this basis, it is thought that ET has
an average annual depth of some 685 to 760 mm (27 to 30 in) in
the Mayacmas Mountains, and about 560 mm (22 in) in the drier
area to the east.
Irrigated crops generally use more water than chaparral. In
the study area, vineyards and orchards are the main crop types.
During the irrigation season (April 1 to September 30), orchards
with cover crops consume some 760 mm (30 in) of water? vine-
yards (wine grapes) use only about 400 mm (16 in); alfalfa and
pasture grass use 760 to 1,015 mm (30 to 40 in) (California
Dept. of Water Resources, 1975).
3.2 GEOTHERMAL CHARACTERISTICS OF THE GEYSERS
Geothermal steam at The Geysers is stored in fractured
greywacke sandstone of the Franciscan Formation. Although in
its unfractured state greywacke has limited capacity to store or
transmit water to wells, when fractured it becomes the principal
169
-------
geothermal aquifer. Other rocks of the Franciscan Formation,
principally serpentine, serve as aguicludes, impairing the flow
of fluid from aquifers.
Although the geothermal wells yield essentially dry steam,
there is evidence that both steam and water coexist within the
fractured rock reservoir. It may be possible that steam is
boiling off of a deeper seated hot water body; conversely,
water may be injected under pressure into the heated rocks and
there flashed to steam. The question of possible recharge to
the reservoir is moot. Answers to the question of natural
recharge will await better data on the rates at which pressure
and flow decline in deep wells across many parts of the field.
To date, data have been released that show declines in pressure
and mass flow primarily from a shallow, older part of the geo-
thermal field.
Well yields, shut-in pressures and calculated enthalpies
are sufficiently constant across a 9.5 km (6 mi) zone of the
geothermal field to suggest that there is relatively free com-
munication through the rock reservoir. As the outer boundaries
of the field are not clearly known, and as it is surely greater
than 47 sq km (18 sq mi) in area, the total of fluid in storage,
even ignoring recharge, is vast.
Development began in the late 1950's with the drilling of
wells to several tens of meters in depth along the northern bank
of Big Sulphur Creek. This was the area from which fumaroles
(natural steam vents) had discharged since prehistoric times.
Well yields were moderate to small, shut-in pressures were low,
and declines in pressure and flow were noticed after only a few
years of production. Careful measurements were thwarted by the
presence of a blowout in the midst of this part of the field.
This well still discharges to the atmosphere under only partial
control.
It has since been recognized that this shallow part of The
Geysers field is supported principally by upward leakage of
steam along faults that penetrate into the deeper field. At
least one of the older, shallow wells has been deepened and now
produces at greater pressure and rate of flow from this deeper
pool.
Wells have been drilled to increasingly greater depths
since the mid-19501 s, and over an ever-widening area. Maximum
depth is over 2,700 m (9,000 ft), and average depth is about
2,100 m (7,000 ft). Rates of flow average between 68,000 and
90,700 kg (150,000 and 200,000 Ibs) of steam per hour. Shut-in
pressures are on the order of 35 to 32 kg/sq cm ( 500 to 450
Ibs/sq in.). Enthalpies often calculate to about the maximum
obtainable for saturated steam conditions. This suggests that
liquid water and steam are in some form of coexistence within
the reservoir rocks.
170
-------
Rates of satisfactory completion are high, averaging four
out of every five holes drilled. Unsuccessful holes usually are
characterized by high temperatures, although steam flow or
absence of steam may occur.
Holes are drilled by rotary drilling method, using mud as
the circulating medium to depths below that of known fresh water
aquifers. Drilling thereupon switches to air. The hole usually
is cased to depths of about 900 to 1,200 m (3,000 to 4,000 ft),
and continued open thereafter. Formation strength is great
enough to support open holes, except in rare cases where caving
or bridging deep within the hole has been noted.
Well spacing has been at 16 ha (40 acre) intervals across
the parts of the field under recent development. It is assumed
that a similar policy will be carried out for the remainder of
the field. Given average well conditions, a single section
(260 ha [640 acres]) appears capable of supporting a 110 MW
electric generating station. No interference is reported
between wells at a 16 ha (40 acre) spacing. It may even be
possible to construct additional wells on a 8 ha (20 acre)
spacing if individual wells suffer declines in pressure or
total flow.
True field life is unknown. Even individual well life is
uncertain and subject to site-specific characteristics. As
individual power generation stations are to be amortized over a
30- to 35-year period, it is assumed that data is available to
the field operators to assure the viability of such investments.
As an analogy, it is known that geothermal pools at Larderello,
Italy, have continued to supply steam to wells for over half a
century.
Even ignoring the question of recharge, it has been shown
that over 85% of the heat is contained in the rock masses, and
less than 15% is present in the fluid phase. Therefore, the
'question of depletion of heat is really a question of rate of
transfer of heat from rock to water. As conductive transfer of
heat is slow, it may be possible to chill individual fracture
surfaces, but it is unlikely that the entire field can be cooled
significantly because of the great quantity of heat stored in
these rocks.
At present some 20% of the geothermal fluid is condensed
and returned to the reservoir via reinjection wells. These
usually are unsuccessful holes drilled for steam and disused
steam wells, as well as specially drilled shallow holes. The
condensed, heat-depleted geothermal fluid is fed by gravity into
wells, where it reenters the formation under hydrostatic head.
The rates and paths by which it recirculates within the reser-
voir are unknown. It is possible that this action,will chill
the reservoir rock very locally; however, in reality, reinject-
171
-------
ion may serve as a form of secondary recovery of heat from the
rock.
The withdrawal of fluid from a rock reservoir may result in
ground subsidence. This has been true in ground water basins,
as well as in reservoirs of oil, gas and geothermal fluid.
Geothermal subsidence is noted at Wairakei, New Zealand.
At The Geysers, the reservoir rocks are hard, locally
metamorphosed sedimentary and igneous rocks. Reservoir fluid is
steam rather than hot water. Therefore, these rocks would not
be affected by a reduction in hydrostatic pressures as much as
would the softer sedimentary and volcaniclastic rocks at
Wairakei. To date, compaction and subsidence has not manifested
itself as a problem at The Geysers, even though pressure has
been reduced in certain shallow parts of the geothermal field.
Further, reinjection of condensates from the geothermal power
plants may prevent significant development of this problem by
partially maintaining mass and pressure within the deep
reservoir.
3.3 GEOLOGY
The geology of The Geysers-Clear Lake regipn is discussed
in this section under the topics of physiography, regional
geologic setting and tectonic history, structure, stratigraphy
and lithology. In general, geology is poorly exposed in this
rugged, heavily vegetated area and numerous generations of
geologists and geophysicists have slowly unravelled an even more
complex pattern of sedimentation, basin deformation, igneous
intrusions and volcanism. Plate 3.1 A and B present a geologic
map and cross sections (McLaughlin, 1974) of The Geysers area.
3.3.1 Physiography
The study region comprises approximately 1,044 sq km (400
sg mi), located in the northern Coast Ranges, within Sonoma,
Lake, Mendocino and Napa Counties, California. This area is
described crudely by a triangle with verticles at Cloverdale,
Calistoga and the northeast side of Clear Lake.
Topography is dominated by northwest trending linear ridges
separated by narrow, V-shaped valleys. Major streams, probably
antecedent, have cut trenches across this northwest-oriented
grain. However, the great preponderance of stream mileage runs
parallel to grain. The Mayacmas Range and southern Clear Lake
basin occupy most of the study region; Napa Valley and northern
Putah Creek Basin occupy its southernmost part.
172
-------
The Mayacmas Range forms the highest range in this region,
with ridge crests commonly above 900 m (3,000 ft) in elevation
and highest peaks above 1,200 m (4,000 ft) (Mount St. Helena
Cobb Mountain). Maximum relief, therefore, is 900 m (3 000 ft)
with 600 m (2,000 ft) of relief common. Slopes are steep and
often unstable and landslide-prone. Ridge crests often are flat
to gently rolling, reflecting an erosion surface cut late in
Tertiary time. Geomorphically, therefore, the Mayacmas Range
exhibits an uplifted submature landscape, incised by youthful,
still downcutting streams.
Clear Lake Basin has considerably lower average elevation
and relief than the Mayacmas Range. Clear Lake has an altitude
of 404 m (1,326 ft), and major tributary valleys rise to some
460 m (1,500 ft). Except for Mount Konocti, which rises to
1,280 m (4,200 ft), maximum elevations on ridges within the basin
are in the neighborhood of 700 m (2,300 ft). Generally, these
are rolling and flat-topped, and, furthermore, a number of
small, flat-floored valleys are present. Therefore, the geo-
morphology of this basin is essentially submature. However,
uplift locally has caused some rejuvenation of erosion, as
evidenced by incised stream channels. Evidently, Quaternary
uplift has been much less here than in the adjoining Mayacmas
Mountains; subsidence accompanying volcanism (described below)
may be the reason.
Putah Creek Basin in the study region is much like Clear
Lake Basin, in terms of overall geomorphic appearance and eleva-
tion. The two basins are separated by a sinuous low divide,
which trends southeasterly from Swigler Mountain. Average eleva-
tion in Putah Creek Basin is somewhat lower, with flat-floored
valleys at about 300 m (1,000 ft).
Napa Valley, which heads on the south flank of Mount St.
Helena, is flat-floored and has an altitude of 110 m (361 ft)
near Calistoga. In overall aspect, it is similar to Alexander
Valley, which flanks the study region on the west.
3.3.2 Regional Geologic Setting and Tectonic History
The history of faulting in this region can be divided into
three periods. The first period entailed chiefly thrust fault-
ing, as the result of compressional forces accompanying subduc-
tion of the Pacific tectonic plate beneath the North American
plate. This occurred from late Jurassic into Eocene time.
Thrust faults separating Franciscan and Great Valley rocks, and
within the Great Valley Sequence, formed at this time, during
the deformation and final obliteration of the Franciscan and
Great Valley depositional basins. These faults tend to have
shallower dips than the other types and have no predominant
trend direction. Serpentine has frequently flowed into these
zones.
173
-------
The second period involves chiefly right-lateral strike-
slip on northwest trending faults; the San Andreas Fault System
is its most well-known expression. This mode of deformation
began in Oligocene time, when the East Pacific Rise collided
with the trench (subduction zone) at the continental margin, and
has continued until the present time. Practically all Coast
Range seismicity originates on northwest trending right-lateral
strike-slip faults.
In the past period, beginning in late Pliocene time, uplift
of the Coast Ranges and volcanic activity of the Clear Lake-
Sonoma Valley region has been accompanied by normal faulting;
this has also continued to the present. Normal faults are
abundant in the Clear Lake Volcanic Field, and are probably the
result of both continued range uplift and basin subsidence. Most
of these faults trend northwesterly, but a number also trend
north-northeasterly. The latter probably formed in response to
volcanic subsidence of the Clear Lake Basin.
Individual faults in the study area rarely are simple
fractures, but rather are zones of varying width and complexity,
along which there has been intense shearing and fracturing of
rock materials. The complexity and intensity of fracturing in
the several episodes of deformation have resulted in intricate
patterns of faulting and highly complex surface geology.
Locally, Franciscan rocks have been sheared and subsequently
altered to a fine-grained, montmorillonite-rich clay matrix,
within which are found coherent boulders and blocks of unal-
tered, unsheared rock. This is known as melange structure.
Beginning in Pliocene epoch, and continuing locally to the
present, there has been differential doming and downwarping of
large portions of the northern Coast Ranges. The Mayacmas Range
has been uplifted sharply, with uplift apparently reaching 900
to 1,200 m (3,000 to 4,000 ft) in places, by evidence from
deformed and offset surfaces. Areas exposing Sonoma Volcanics
appear to have subsided, at least in part, with the upper sur-
face of Franciscan rocks depressed by several tens to a few
hundred meters. The area around Clear Lake, northeast of the
Mayacmas Range, appears also to have subsided (or collapsed,
depending upon interpretation) tectonically. Both of these
downwarped areas may have moved in response to withdrawal of
magma from large underground chambers. The uplift of the
Mayacmas appears in part to have originated with magmatic dom-
ing, although other tectonic stresses undoubtedly were involved.
This differential vertical movement seems to have occurred
principally along the northwest trending faults previously
active in strike-slip movement. Accompanying vertical (or
near-vertical offset) has been rotation of blocks, such that for
a large area west from the Mayacmas crest, blocks have rotated
to the northeast or east. Northeast of the Mayacmas Range,
174
-------
blocks have subsided (Clear Lake), but the component of rotation
along vertical faults is unknown.
3.3.3 Structure
The Coast Ranges are cut by numerous linear, steeply dip-
ping, predominantly northwest trending faults. Most of these
are strike-slip (lateral displacement) faults, but some are of
the normal or reverse type (essentially vertical displacement).
A few of these are recognized as being seismically active. The
best known active fault is the San Andreas, 71 km (44 mi) west
of the study area at its closest point of approach, which
extends for about 1,130 km (700 mi) from Imperial Valley to near
Cape Mendocino, and has been the source of many strong to great
earthquakes in historic time. Although certain additional
faults are considered active, most faults are believed to have
ceased activity in earlier geologic epochs, based upon the
available geologic data. A number of minor faults displace
units of the Clear Lake Volcanic Series, and some of these
should be considered potentially active.
Regional dips at The Geysers are northeasterly. Farther to
the south and west a reversal in dip to the southwest is noted
(McLaughlin, 1974). Therefore, an anticlinal structure may be
recognized (commonly called an antiform), cut by numerous faults
along which rotation of individual blocks has occurred. It is
the sense of rotation that gives rise to the antiform. This
structure is believed to plunge to the southeast. Therefore,
the greatest structural relief is noted at the northwest end of
the structure, near The Geysers.
Other plunging blocks may exist parallel to The Geysers
antiform. A regionally downdropped block is northeast of the
Collayomi Fault and is here called the Clear Lake-Middletown
Lowland. It consists of Great Valley Sequence rocks, atop
imbricated, serpentinite-soled thrust sheets, and probably in
turn atop Franciscan rocks. Nowhere is Franciscan rock exposed
in this lowland block.
3.3.4. Stratigraphy and Lithology
Franciscan Formation—
Basement in the region consists of the Franciscan Formation
and associated rocks of late Mesozoic age. Franciscan sedimen-
tary rocks, in approximate order of abundance, are greywacke,
shale, conglomerate, chert and very minor lenses of limestone.
Interbedded and intruded into these sediments are basalt, dia-
base, gabbro and related mafic crystalline rocks, as well as
masses of serpentinized peridotite and pyroxenite, and exotic
boulders of eclogite.
175
-------
It is believed that Franciscan sediments accumulated in a
deep water oceanic trench, perhaps similar to that off of
present-day Chile or Japan. Sorting of sediment is poor and
bedding features are weakly developed to nonexistent.
Greywacke, which comprises about 60% of the entire
sequence, is massive, poorly bedded, poorly sorted and,as a
result, nonporous. (This rock forms the geothermal reservoir).
Greywacke consists of approximately equal amounts of quartz,
feldspar and lithic fragments (preexisting chert and quartz
porphyry, and cannibalized Franciscan greywacke and shale) in a
matrix of the same materials ground very fine. Unsheared Fran-
ciscan greywacke contains very little clay mineral in its
matrix.
Shale is, in reality, a microgreywacke, consisting of the
same materials as greywacke matrix, in finer grain size. Shale
crops out irregularly, but often is identified in well cuttings
and in deep road cuts. Therefore, it may be more abundant than
recognized.
Undersea eruptions and intrusions of mafic lavas resulted
in formation of igneous sheets, necks, dike complexes and stocks
within Franciscan sediment. Volcanically induced changes in
composition and temperature of sea water are believed to have
resulted in the episodic precipitation of chert. Chert is well
but thinly bedded, and interleaved with very thin partings of
shale. Soft-sediment crumpling within the trench resulted in
extreme contortions of bedding. The resistant chert appears
more abundant on the surface than in cross section.
Igneous rocks are all mafic to ultramafic in composition.
Tuffs and other ejecta are rare. Ultramafic rocks are believed
to be portions of the Mesozoic subcrust which intruded and/or
were tectonically crumpled into the complex of sediment and
mafic lava. Mafic igneous rocks may form 15% to 20% of the
entire Franciscan assemblage. Ultramafic rocks, although very
recognizable and widespread at the surface today, are believed
to be less abundant overall.
Fossils are rare in this deep-water assemblage. However,
rare fossils and radiometric age-dates suggest that deposition
began in late Jurassic time and continued probably to late
Cretaceous time and possibly into Paleocene epoch.
Subduction of trench sediment and igneous rocks is believed
to have occurred rapidly. This is invoked to account for (1)
extreme shearing, (2) low-temperature, high-pressure metamor-
phism, (3) complex deformation and juxtaposition of the Fran-
ciscan materials, as well as (4) intrusion of eclogite masses
and (5) present-day distribution of the Franciscan with regard
to other formations.
176
-------
Metamorphism has resulted in widespread development of
zeolite facies in Franciscan greywacke and shale; and in local-
ized development of blueschist facies (characterized principally
by lawsonite and glaucophane). Mafic igneous rocks have been
converted to greenstone, with common soda metasomatism, perhaps
as a result of reaction with contained seawater. Serpentini-
zation of ultramafic rocks may have occurred then or at a later
time under near-surface conditions. Very local, and anomalous,
development of greenschist facies (epidote-albite-tremolite-
quartz) in sedimentary and igenpus rocks also may date from the
period of subduction, as relatively small masses were heated to
higher than normal temperatures, or were intruded from greater
depths.
Deformation during this cycle is believed by many to have
destroyed stratigraphic continuity or identity and to have
created "tectonic" units. These consist of broken slabs of
various size and stratigraphic position, rotated, sheared inten-
sively, juxtaposed irregularly and set in a fine-grained
matrix. These tectonic units are referred to as melange. An
important consideration is the development of chlorite and clay
minerals within the melange matrix. Coherent slabs may range
from fist-size to hundreds of square meters in extent, set in
highly sheared matrix. The resultant melange is highly unstable
and tends to fail in steep slopes or when cut.
Franciscan and equivalent rocks are exposed across an area
of 104,000 sq km (40,000 sq mi) or more, extending from south-
western Oregon to the Los Angeles basin and perhaps beyond.
Franciscan rocks are believed to underlie an equivalent area,
onshore and offshore, having a total area of perhaps 207,000 sq
km (80,000 sq mi). Nothing has ever been observed to underlie
Franciscan rocks. Seismic profiles run across northern Cali-
fornia in the early 1960ls suggested that materials of mantle or
near-mantle densities (perhaps mafic intrusions or ultramafic
sheets) underlie rock of Franciscan densities at depths of 14 to
21 km (9 to 13 mi). Observed and calculated thicknesses of
Franciscan rocks are on the order of 1,500 m (5,000 ft), which
agrees closely with the seismic profiles.
Great Valley Sequence—
While the Franciscan Formation was being accumulated in a
deep water trench, another sequence of rock was deposited in a
near-shore marine environment east of the trench, perhaps simi-
lar to the present continental shelf and slope. This group of
sandstone, shale, siltstone and conglomerate is also of late
Jurassic to late Cretaceous age and is known collectively as
the Great Valley Sequence, from its principal areas of exposure
along the western margin of the Great Valley. This sequence of
rocks may be up to 10,700 m (35,000 ft) thick. Relatively minor
amounts of basalt, diabase, and chert are present in its lowest
portion.
177
-------
Formation names have been applied locally. The Knoxville
Formation, of upper Jurassic age, is recognized widely and often
is found in tectonic contact with equivalent-age Franciscan
rocks. The Knoxville rocks consist of dark shale and light
colored siltstone, rhythmically interbedded and having a dis-
tinctive outcrop pattern. Higher in the Great Valley Sequence,
massive sandstone and conglomerate beds are abundant, along with
lenses of fossiliferous limestone. Units of all lithologies
often are lensing, and some are time-transgressive. This has
resulted in development of two distinctive systems of nomencla-
ture: one based on fossil content, independent of lithology, and
another based upon lithology, independent of stratigraphic
continuity.
Mafic volcanic and ultramafic rocks, often serpentinites,
are present near the base of the Great Valley Sequence, in the
Knoxville Formation. These crystalline rocks are indistinguish-
able from those in the Franciscan and may have identical
sources. In proximity to these mafic and ultramafic rocks,
Knoxville sediments are deformed and sheared to a degree com-
parable to the Franciscan.
The Knoxville Formation may reach 6,100 m (20,000 ft) in
thickness, and the total Great Valley Sequence may be 9,100 m to
12,200 m (30,000 to 40,000 ft) thick. The best exposures of the
sequence are at the east end of the Coast Ranges, where the
sequence dips homoclinally beneath the Central Valley.
It is believed that destruction of the Mesozoic trench at
the beginning of Tertiary time was accompanied by shearing,
compressive folding, and imbricated thrust faulting, in which
Great Valley and Franciscan rocks were intricately deformed
together. Commonly, the Franciscan is described as having been
underthrust beneath Great Valley rocks. Serpentinized perido-
tite is believed to have served as the lubricated sole of the
thrusts. Indeed, serpentinite or a sheared mixture of serpen-
tinite, greenstone and fault gouge usually is present between
Franciscan and Great Valley rocks wherever they are observed in
close proximity.
Thrusting of Franciscan beneath Great Valley rocks is a
concept required by the finding that these rocks are in part
contemporaneous and by the fact that depositional contact
between the two formations has never been demonstrated. Wher-
ever they are in contact, a fault or serpentinite body inter-
venes. Swe and Dickinson (1970) adopted and refined this con-
cept and described the Great Valley Sequence, as exposed in the
Lower Lake 15-minute quadrangle, as a series of four main
stratigraphic units which has been complexly folded and broken
into three or more thrust slices. Although there is no evidence
within the area to indicate when regional thrusting began, it is
believed to have begun by late Cretaceous time. Field relation-
178
-------
ships at Round Valley, 120 km (75 mi) to the northwest, suqqest
that regional thrusting persisted into early Oligocene time
(perhaps 35 to 38 million years ago).
Tertiary Sedimentation—
Local basins of marine sedimentation persisted after the
destruction of the regional basins that began in late Cretaceous
time. Marine sediments of Paleocene and Eocene age (38 to 65
million years in age) are found scattered across parts of the
northern Coast Ranges. Within 6 km (4 mi) south and east of
Lower Lake, these are represented by the Martinez and Tejon
Formations, of Paleocene and Eocene age, respectively. Accord-
ing to Brice (1953), who mapped the Lower Lake quadrangle in the
late 1940's, the Martinez Formation is composed of massive
sandstone beds, with some conglomerate and shale in its upper
portion; its maximum thickness is 1,300 m (4,250 ft). The Tejon
Formation is a white, conglomeratic sandstone, with a maximum
thickness of 370 m (1,200 ft). Depositional environment for both
formations apparently varied from shallow marine to continental,
indicating that uplift of the region had begun.
The entire region must have been raised above sea level by
the close of Eocene time (38 million years ago), because, other
than limited deposits of Miocene and Pliocene age near the
present coast line, no marine sediments younger than Eocene are
known in the northern Coast Ranges. In late Pliocene or early
Pleistocene time, probably no more than 4 million years ago, a
basin larger than and including the present Clear Lake Basin
began to accumulate freshwater sediments now called the Cache
Formation. This is composed predominantly of gravel, silt, and
sand, but water-lain tuffs (volcanic ash) and tuffaceous sands
become dominant near the top of the formation; these are inter-
calated with clay, marl, pebbly limestone and diatomite.
Apparently the Cache Formation was deposited by streams
entering one or more tectonic or structural basins, and whose
surface was covered from time to time by lakes and swamps
(Brice, 1953). The fine-grained rocks at the top of the unit
are lake deposits. The maximum thickness of the Cache beds was
calculated (Brice, 1953) to be 1,980 m (6,500 ft), which is
unusually great for a freshwater deposit. Work in progress by
geologists of the USGS suggests a downward revision in thickness
of the Cache Formation.
Pliocene and Quaternary Volcanism—
Volcanic activity in the region began with the eruption of
the Sonoma Volcanics in Pliocene time, during the period from 6
to 3 million years ago. These deposits covered an elliptical
area extending from just north of San Pablo Bay to the vicinity
of Healdsburg and Calistoga. They consist of basalt, andesite
and rhyolite lava flows and ash, interbedded with volcanically
derived sediment. The northern part of the Sonoma Volcanics, in
179
-------
the vicinity of Mount St. Helena, is principally rhyolite tuffs
and dacite tuffs and flows, cut by small intrusions of similar
composition.
Thickness of Sonoma rocks varies greatly, from a few tens
of meters to hundreds of meters. The greatest thicknesses are
believed to be located north of Calistoga, and to reach 900 to
1,500 m (3,000 to 5,000 ft) at a maximum. This may have been the
central vent area for late-stage Sonoma eruptions.
Paleobotanical and vertebrate evidence, as well as potas-
sium-argon (K-Ar) age-dates, suggest that Sonoma Volcanism has
migrated northward during the Pliocene epoch. Inception was
about 8 million years before present (mybp) at the south end of
Napa Valley. The youngest dated Sonoma rocks are 2.9 million
years, from the slopes of Mount St. Helena at the northern edge
of the Sonoma Volcanics. Rocks of intermediate ages are known
from locations between these points.
In early Pleistocene time, a period of largely silicic
volcanism began south of Clear Lake, forming the Clear Lake
Volcanic Series. Clear Lake Volcanism appears to have begun
with the eruption of unique, low-viscosity, quartz-bearing
olivine basalts. Its age is given as early Pleistocene. These
flowed into and onto Sonoma terrain. A period of dacitic-andesi-
tic volcanism followed, succeeded about 500,000 years ago by a
major period of silicic volcanism. This included eruption of
rhyolite glass flows and tuffs and dacite flows and tuffs and
extrusion of rhyodacite domes. Still more recent are obsidian
flows, of approximately 100,000 years of age. Youngest of all
are well-preserved cinder cones and maars, perhaps in the age
range of 10,000 to 40,000 years, located at the southern and
eastern edges of Clear Lake.
Evidence suggests northward migration of magmatism in
Pleistocene time. For example, Cobb Mountain (K-Ar age-date of
1 mybp) and the quartz-bearing olivine basalts are at the south-
ern end of the Clear Lake Volcanic Series. Northward are the
one-half million year old silicic lavas and domes. Still farther
north and northeast are the youngest mafic and silicic cones and
flows. This appears to extend the northward progression that
began near San Francisco Bay at the end of Miocene time.
Clear Lake Volcanic Series rocks are not as widespread or
thick as the Sonoma Volcanics. In many places, thickness is but
a few tens of meters except around vent sources. The greatest
recorded thickness is 730 m (2,400 ft) in the KettenhofenNb. 1
well near Mount Konpcti. Total thickness in that area may be
900 m (3,000 ft), with greater thickness for plugs and volcanic
necks.
180
-------
Several discrete centers of rhyolite, dacite and andesite
volcanism are recognized, including Cobb Mountain Mounts
Hannah, Siegler and Konocti and Boggs Mountain, in addition
there are numerous smaller basaltic cinder cones. Widely dif-
fering degrees of erosion of these ancient volcanoes attest to
a span of activity covering much of the Pleistocene epoch
Mount Konocti is deeply eroded, Cobb Mountain is somewhat less
eroded, and Mounts Hannah and Siegler are only somewhat eroded.
However, morphology does not correlate very closely with time of
youngest volcanic activity: radiometric age-dates for rocks of
the Clear Lake Volcanic Series range from 0.03 to 2.5 mybp. The
rhyolite of Borax Lake is dated at 0.08 mybp (Hearn, et al.,
1975).
Although maximum thickness of extruded lava and ash is
probably less than 760 m (2,500 ft), intrusive necks and stocks
may extend downward to great depth and may be fingers rising
away from a much larger, possibly molten, igneous body at depth.
The minimum depth of this hypothetical body (often referred to
as the Clear Lake Batholith) may be 5 to 8 km (3 to 5 mi), based
on nonconclusive evidence. This hypothetical intrusive mass, and
the stocks of the several extrusive centers mentioned above, may
form the heat source for the geothermal field.
Quaternary Sediments—
Lacustrine deposits in Clear Lake and the adjacent closed
depression may be the oldest Quaternary sediments in the region.
More recent deposits are sand, gravel and silt deposited in
stream channels, as fans abutting the mountains and as valley
fill.
3.4 HYDROLOGY
The study area comprises portions of four drainage basins:
that of the Russian River on the west, which empties into the
Pacific Ocean; Cache Creek and Putah Creek Basins, which drain
the east flank of the Mayacmas Mountains and flow easterly into
the Sacramento River; and the Napa River, which heads on the
flanks of Mount St. Helena and flows southeasterly into San
Pablo Bay.
Practically all precipitation either becomes stream runoff
or is stored temporarily in soil zones, from which it is evapo-
rated and transpired. A very small amount percolates downward
to join ground water reservoirs in permeable rocks and alluvium.
Most shallow ground water is stored in shallow alluvium which
occurs in valleys flanking the Mayacmas Mountains.
181
-------
3.4.1 Surface Water
Stream Flow—
Numerous stream-gaging stations have been operated for 20
to 30 years in the study region. Table 3.2 presents average
annual discharge data for eleven streams draining the Mayacmas
Mountains.
Depth of runoff (see Table 3.2) amounts to some 635 mm (25
in) on the east side of the Mayacmas Mountains, and 785 mm (31
in) on the west side. Roughly, this amounts to about one-half
of total precipitation. In the drier region extending between
Lower Lake and Middletown, runoff depth is about 355 mm (14 in)
annually, occurring as about 40% precipitation. Runoff depth of
300 mm (11.8 in) was computed for the land surface of Clear
Lake Basin, by correcting the discharge of Cache Creek for
evaporation from and precipitation on the lake surface (evapora-
tion from the lake is estimated at 914 mm [36 in ] annually).
3.4.2 Groundwater
Groundwater data for the study region is quite limited,
both geographically and temporally. Water wells are located
almost entirely within the narrow alluviated valleys that flank
the Mayacmas Mountains, and published records for them cover
only a few years. Generally, these wells penetrate only allu-
vium, which rarely is deeper than about 75 m (250 ft). There-
fore, information concerning groundwater in bedrock, which is
more widely exposed than alluvium, is nearly nonexistent.
In the following, groundwater in each of the major alluvi-
ated valleys is discussed on an individual basis. Finally,
groundwater conditions in bedrock areas of the Mayacmas Moun-
tains are treated in a necessarily speculative manner. Valleys
treated are listed here by county: in Lake County, Big Valley,
High Valley, Excelsior Valley, Burns Valley, Borax Lake Basin,
Collayomi Valley and several small flats southeast of Mount
Konocti; in Sonoma County, Alexander Valley; in Napa County,
upper Napa Valley (near Calistoga).
Big Valley—
Big Valley is a gently rolling plain, sloping northward
into Clear Lake and encompassing some 8,100 ha (20,000 acres).
Elevations range from 400 to 460 m (1,320 to about 1,500 ft).
Kelsey, Highland, and Adobe Creeks are the major drainages, but
there are a number of other minor creeks as well. All manifest
seasonal—that is, not perennial—flow.
Principal geologic units in this valley are the Mesozoic
basement rocks of the Franciscan Formation, the Plio-Pleistocene
sedimentary Cache Formation, the Pleistocene Clear Lake Volcanic
Series and Quaternary unconsolidated sediments, including lake,
terrace and stream deposits. The young, mostly permeable un-
182
-------
TABLE 3.2 AVERAGE ANNUAL STREAM DISCHARGE1 AND DEPTH OF RUNOFF
oo
Co
DRAINAGE
AREA
STREAM (sq mi)
Russian River Basin
Big Sulphur Creek 82
Russian River (Healdsburg) 793
Maacama Creek 43.4
Putah Creek Basin
Putah Creek 112
Dry Creek 8.4
Cache Creek Basin
Cache Creek 528
Highland Creek 12.7
Kelsey Creek 37.2
Adobe Creek 6.4
Seigler Creek 12.5
Copsey Creek 13.2
Burns Valley Creek 4.4
Napa River Basin
Napa River (2.5 mi 81.4
east St. Helena)
DISCHARGE
(acre-ft)
147,000
1,043,000
67,740
148,000
21,230
251,400
15,570
54,270
9,060
9,420
9,830
1,110
68,390
DEPTH OF
RUNOFF
(in
33.6
24.7
29.3
24.8
47.4
11.8'
23.0
27.3
26.5
14.1
14.0
4.7
15.8
1) Data from USGS (1976)
2) Computed for land surface adjacent to Clear Lake,
by correcting for evaporation and precipitation on the lake.
-------
consolidated sediments reach a maximum thickness of 65 m (213
ft) north of Kelseyville; older Quaternary and Cache deposits
are about 150 m (500 ft) thick. Thickness of the underlying
volcanic rocks is unknown but is probably less than 460 m
(1,500 ft).
Principal occurrence of ground water is in the younger,
coarser-grained Quaternary sediments. Much of the ground water
is unconfined, but confined areas exist locally where extensive
layers of clay are present near the land surface. Within the
older Quaternary sediments (largely terrace gravels, lake and
floodplain deposits of fine sand, silt and clay), perched
ground water occurs in the more permeable materials. Within the
older lake deposits, a thin bed of lithic tuff, 0.6 m (2 ft)
thick, forms a permeable and widespread aquifer. Only two wells
are known to tap water from the volcanic rocks on Cameback
Ridge. These rocks are highly fractured and yield significant
quantities of water; however, on account of their depth, they
are not encountered by any of the wells in Big Valley. While
Franciscan basement is fractured and therefore probably has
significant permeablity, no data on its hydraulic properties is
available.
Although not stated explicitly in the documents consulted
(California Department of Water Resources, [1957]; Soil Mechan-
ics and Foundation Engineers, Inc., [1967]), the ground water
reservoir as known and utilized extends from the land surface to
a depth of some 30 m (100 ft). To this depth, total storage
capacity is 14,260 ha-m (118,500 acre-ft), and average specific
yield is 8% (California Department of Water Resources, 1957).
Water levels, and hence water in storage, vary seasonally,
being highest in the spring and lowest in the fall. Average
seasonal lowering of the water table varies from 3 to 7.5 m (10
to 25 ft), depending on location. No long-term decline in water
level has been observed. Therefore, for the period of record
(1949-60), recharge has equaled discharge. Average depth to
the water table is near zero in the spring and 6 m (20 ft) in
the autumn.
Recharge to the Big Valley ground water reservoir occurs
principally by infiltration of water in the channels of Kelsey
and Adobe Creeks. Mean annual surface water inflow from these
and three other, minor creeks is about 7,400 ha-m (60,000
acre-ft). Direct precipitation contributes about 3,700 ha-m
(30,000 acre-ft). A certain amount of recharge must occur as
underflow from bedrock in the flanking uplands, but no quantita-
tive estimates of this are available.
As mentioned previously, average annual discharge and
recharge are equivalent. Although explicit figures for these
factors are not available, a lower limit may be deduced from the
184
-------
mean seasonal fluctuation of water in storage. This has been
estimated as 1,700 ha-m (14,000 acre-ft), based on water-level
changes, specific yield, and reservoir area (Soil Mechanics and
Foundation Engineers, Inc., 1967). Of course, this figure does
not include annual water throughout, which moves through the
basin into Clear Lake as underflow. Since total well pumpage is
unknown, it is not possible to say what fraction of the 1,700
ha-m (14,000 acre-ft) is man-induced and what is naturally-
occurring discharge within the basin. Movement of ground water
is essentially northward toward Clear Lake.
High Valley—
High Valley is a nearly closed basin lying just north of
Clearlake Oaks. It is a flat to gently sloping alluvial plain
of about 810 ha (2,000 acres), with a total drainage area of
some 31 sq km (12 sq mi); its average elevation is about 120 m
(400 ft) above that of Clear Lake. Several short, intermittent
creeks drain the surrounding hills; only in the wettest periods
does surface water flow out of the valley into Clear Lake,
through Schindler Creek.
Geologically, the valley consists of a thin deposit of
stream alluvium and lake sediments resting on Franciscan base-
ment; maximum depth to basement is about 30 m (100 ft), or a
little more. Much of the alluvium is fine-grained and nearly
impermeable; permeable lenses of gravel are located along the
valley margin.
Nearly all ground water used is pumped from wells in the
alluvium. Water levels near the valley center have seasonal
fluctuation of some 6 to 15 m (20 to 50 ft). Because there is
little artificial draft on the ground water body, there must be
considerable natural summer discharge by underflow (Upson and
Kunkel, 1955); probably this occurs mainly through the volcanics
to the east rather than as underflow in Schindler Creek.
Valley East of Clearlake Oaks—
Immediately east of Clearlake Oaks lies a small unnamed
valley, which is actually part of Clear Lake Basin, with a total
drainage area of about 1,600 ha (4,000 acres); 400 ha (1,000
acres) is alluvial plain.
The entire drainage area is underlain by Franciscan Forma-
tion, which is considered non-water- bearing in this region
(Upson and Kunkel, 1955). Therefore, alluvium is the only
significant water-bearing unit. Little information on its
thickness or lithology is available, but it is probably some
tens of meters thick. Depth to ground water is less than 8 m
(25 ft) at most places, and the water is unconfined.
185
-------
Borax Lake Basin—
Borax Lake lies in a closed basin from 1.5 to 3 km (1 to 2
mi) north of Clearlake Park. Total drainage area is some 5 to
6.5 sq km (2 to 2.5 sq mi), and most of the basin floor is
occupied by Borax Lake. The alluvium is underlain by Franciscan
rocks at a maximum depth of perhaps 23 m (75 ft). Borax Lake
and Burns Valley are separated by a low rise comprised of late
Quaternary flows of rhyolite and obsidian. Young cinder depos-
its and historic solfataric activity in this area indicate that
these volcanics were vented very locally. Before eruption of
these rocks, Borax Lake Basin and Burns Valley were connected
and both part of Clear Lake Basin. Now, however, Borax Lake
Basin is a closed depression.
Burns Valley—
This is a long, narrow valley traversed by intermittent
unnamed creeks that flow into Clear Lake. The tributary drain-
age area is about 31 to 32.5 sq km (12 to 12.5 sq mi), about 400
ha (1,000 acres of which are covered by alluvium). The name
"Burns Valley Creek" in Table 3.2 refers to the collector stream
flowing into Clear Lake.
The drainage area of Burns Valley is underlain by the
Franciscan Group, the Cache Formation and some basaltic rocks.
At most places, alluvium rests directly upon the Cache Forma-
tion, and these are the chief water-bearing units here. The
alluvium is nowhere more than 15 m (50 ft) thick. Although more
permeable than the Cache beds, the alluvium has such a small
saturated thickness that water storage in it is quite limited;
small to moderate yields are available from the Cache Formation,
which is at least 60 m (200 ft) thick and probably stores more
water.
Well records (Upson and Kunkel, 1955) show that water
levels average from 1.5 to 4.5 m (5 to 15 ft) below land sur-
face and have a seasonal fluctuation of 1.5 to 2.5 m (5 to 8
ft). Total volume of water in storage is estimated at 6,200 to
9,300 ha-m (50,000 to 75,000 acre-ft). Well pumpage was only
about 4 ha-m (30 acre-ft) per year in 1949 and may not be much
more than that today. No net depletion of the reservoir should
occur at withdrawal rates several times larger, since surface
runoff is some 135 ha-m (1,100 acre-ft) annually.
Excelsior Valley—
This irregularly shaped valley lies from one to two miles
south of Lower Lake. It is drained by Copsey Creek, a small
intermittent tributary to Cache Creek. The valley comprises
north and south portions, separated by a low bedrock ridge
through which Copsey Creek has cut a channel. The alluviated
area of the valley comprises some 570 ha (1,400 acres); the
total drainage area is about 36 sq km (14 sq mi).
186
-------
The drainage area of the valley is underlain by sandstone
and shales of the Cretaceous Great Valley Sequence and the
Eocene Martinez Formation. Drilling reports indicate that these
rocks are "dry" (Upson and Kunkel, 1955). The lava plateaus at
the southeast end of the valley have not been tapped by wells.
However, the lavas absorb precipitation and store it in joints;
in a few places this water discharges as springs. Maximum
thickness of alluvium in the valley is estimated at less than
7.5 m (25 ft), and it is the only significant water-bearing
material. However, as it is predominantly a fine-grained flood
plain deposit, producing wells are nearly all near the valley's
edge, where coarser sediments are present.
Ground water in the valley is unconfined and stands at
levels 3 to 5 m (10 to 17 ft) below the land surface. Storage
capacity is quite small in the thin alluvial cover, probably
less than 250 ha-m (2,000 acre-ft). All ground water comes from
rainfall in the drainage area, which enters storage largely by
direct infiltration on the alluvium and seepage from hillslopes.
Water does not come from other basins by underflow, nor does
much enter by percolation in the bed of Copsey Creek.
Only one well pumps significant water, but this amounts to
only a few tenths of a hectare-meter per year.
Small Flats South of Mount Konocti—
Bonfield,Hesse,Ely and Manning flats are south of Mount
Konocti. Manning Flat is a small alluvial plain located about 8
km (5 mi) west of Lower Lake, with a drainage area of about 5 sq
km (2 sq mi); the plain covers 80 ha (200 acres). It was a
closed basin containing an intermittent lake until about 100
years ago, when a tunnel was constructed to drain it into nearby
Thurston Lake. This flat comprises a less than 6 m (20 ft)
thick silt layer resting upon rhyodacite of the Clear Lake
Volcanics. No significant amount of ground water is stored in
either of these materials (Upson and Kunkel, 1955); one 60 m
(200 ft) deep well was dry.
Bonfield, Hesse and Ely Flats, west of Manning Flat, are a
series of shallow basins along the channel of Thurston Creek,
which flows into Thurston Lake. Total drainage area is about 31
sq km (12 sq mi). The flats are underlain by alluvium which is
less than 6 m (20 ft) thick and generally poorly sorted or
fine-grained. Except for one well in Hesse Flat, wells that
penetrate the alluvium have small yields. The alluvium rests
upon either rhyodacite or rhyolite obsidian of the Clear Lake
Volcanic Series. Only the obsidian yields significant water,
and this underlies Hesse and Bonfield, but not Ely, Flats.
Ground water occurs in the alluvium of all three basins, in
the obsidian bordering Bonfield and Hesse Flats, and presumably
in rhyodacite at depths greater than 60 m (200 ft). In most
187
-------
wells, water levels are 3 to 6 m (10 to 20 ft) below the surface
and water is unconfined. The water table in the obsidian seems
to be shallow but may be perched. Insufficient data exists to
make a satisfactory estimate of water in storage or depth of the
main water body.
Collayomi Valley—
Collayomi and Long Valleys are arms of the same depression
in the headward part of the Putah Creek drainage. Collayomi
Valley, the larger of the two, extends from approximately 5 km
(3 mi) west to 6.5 km (4 mi) south of Middletown. It has a
drainage area of 140 sq km (54 sq mi); of this, the alluvial
plain covers about 10 sq km (4 sq mi). Major streams in the
valley are St. Helena and Dry Creeks, which head south of
Middletown and are tributaries of Putah Creek; Putah Creek flows
through the west arm of the valley and heads about 11 km (7 mi)
northwest of Middletown.
The drainage area is underlain by non-water bearing sand-
stone, shales and serpentinites of the Knoxville (Great Valley
Sequence) and Franciscan Formations. Alluvium reaches a maximum
depth of perhaps 75 m (250 ft) and is the only significant
water-bearing unit. However, fine-grained materials (silts and
clays) seem to predominate near the valley axis, and so nearly
all ground water is stored near the valley margins and along the
channels of Putah and St. Helena Creeks, where sands and gravels
are predominant.
The ground water table is shallow, averaging 4.5 m (15 ft)
deep in midsummer, and seasonal fluctuations are generally about
1.5 m (5 ft). Most developed ground water is pumped from sumps
dug in along the channels of St. Helena and Putah Creeks? these
yield from 760 to 1,900 1pm (200 to 500 gpm). Gross storage
capacity may be some 3,700 ha-m (30,000 acre-ft), but usable
capacity would be considerably less. Considering minimum natu-
ral ground water discharge in stream channels, in the driest
month (July), Upson and Kunkel (1955) estimated that at least
135 ha-m (1,100 acre-ft) per year could be discharged artifi-
cially, without long-term depletion. This is much more than was
being utilized in 1955.
Alexander Valley—
This valley lies along the west base of the Mayacmas
Mountains. It is about 32 km (20 mi) long, with an average
breadth of 1.5 to 2.5 km (1 to 1.5 mi), and the Russian River
flows through its entire length. Numerous streams enter the
valley from both sides; Big Sulphur Creek is the largest drain-
age from the Mayacmas Mountains; Maacama Creek is also
significant.
Geologic formations underlying the valley include the
Franciscan and Knoxville Formations, massive conglomerates of
188
-------
Cretaceous (?) age, the Sonoma Volcanics, the Glen Ellen Forma-
tion and various stream alluvium deposits. The alluvium bears
the most water, and wells near the river, where deposits are
coarsest, yield from 760 to 1,900 1pm (200 to 500 gpm)- its
maximum thickness exceeds 18 m (60 ft).
Ground water occurs under water table conditions
(unconfined) over most of the valley but may be locally semi-
confined by overlying deposits of silt and clay (Cardwell,
1965). At most places, water levels are 1.5 to 4.5 m (5 to 15
ft) below the land surface in the spring and about 1.5 m (5 ft)
deeper in the summer.
Water also occurs in limited quantities in older forma-
tions. Most important is the Glen Ellen, encountered at depths
of 18 to 120+ m (60 to 400+ ft), which yields up to 1,500 1pm
(400 gpm). Many wells in the southern part of the valley pro-
duce from this formation. The Cretaceous (?) conglomerate
yields moderate flows; no data on the hydrologic characteristics
of older formations is available, as they have not been drilled.
Storage in alluvium has been estimated as some 6,200 ha-m
(50,000 acre-ft). Discharge by natural means (discharge to the
river, underflow at the south end of the valley and evapotrans-
piration) probably exceeds artificial discharge (principally by
irrigation wells) by a sizeable amount (Cardwell, 1965). Well
pumpage in 1964 was roughly 370 ha-m (3,000 acre-ft); clearly,
recharge by rainfall, infiltration in stream beds and underflow
is considerably greater than this amount.
Upper Napa Valley—
As discussed here, upper Napa Valley comprises the area
extending from Calistoga to the uppermost end of the valley, and
has an area of about 13 sg km (5 sq mi). Average elevation on
the valley floor is nearly 120 m (400 ft) and rises to between
600 and 1,300 m (2,000 and 4,300 ft) on flanking mountains. The
area is drained by the Napa River, which flows throughout the
length of Napa Valley.
The Pliocene-age Sonoma Volcanics cover most of the
uplands, while the valley is covered by Quaternary alluvium. The
alluvium is underlain by volcanics, and the volcanics are under-
lain by the Franciscan Formation throughout the drainage area.
The most important water-bearing units are within alluvium
and the Sonoma Volcanics. Permeable horizons in the Pliocene
sedimentary section (in the Huichica and Glen Ellen Formations)
form rather low-yield aquifers in the southern part of the
valley but are not present near Calistoga. The Franciscan and
Knoxville Formations are virtually non-water-bearing in this
area (Kunkel and Upson, 1960). In the Calistoga area, many of
the wells produce from the Sonoma Volcanics, particularly from
189
-------
welded tuffs of the St. Helena rhyolite member; the St. Helena
rhyolite is several tens of meters thick in the vicinity of
Calistoga. In general, pumice and tuff are the main aquifers in
the Sonoma Volcanics, while flows are poor yielders.
Ground water storage and recharge/discharge data specific
to the Calistoga area are not available; parameters covering the
entire valley are available (Kunkel and Upson, 1960) but really
are not helpful here. Generally, however, water levels have an
average depth of 7.5 m (25 ft).
Mayacmas Mountains—
Rocks of the Franciscan Formation form the preponderance of
outcrops in the Mayacmas Mountains, particularly in the vicinity
of The Geysers geothermal field. Lithplogy in this formation
includes sedimentary, metamorphic and igneous types: greywacke
sandstone, basalt and serpentinite are the three most abundant.
None of them has primary porosity; water is stored in small
quantities in joints and fractures induced by late Cenozoic
tectonism.
Numerous springs in the Mayacmas Mountains indicated that
ground water is present; these meet most domestic and stock-
watering needs in the mountains. Few water wells have been
drilled into Franciscan rocks, but those have yields in the
order of 3.8 1pm (1 gpm). This is in the order of 1% of that of
wells producing from unconsolidated materials, with specific
yields in the neighborhood of 8%. Therefore, an order-of-magni-
tude specific yield for Franciscan rocks is estimated to be some
0.1%.
3.4.3 Hydrologic Budget
By comparing precipitation (P), depth of runoff (RO) and
depth of evapotranspiration (ET), it may readily be seen that,
across the study area,
P s RO + ET
This equation does not take into account variations in soil
moisture and ground water storage, or ground water discharge.
The complete hydrologic balance is expressed by the equation
P = ET + RO + ASMS + AGWS + GWD
where A SMS = change in soil moisture storage
A GWS = change in ground water storage
GWD = ground water discharge
Complete solution of the equation requires much more detailed
and complete data than is available to this study.
190
-------
The Placer County study (Lewis and Burgy, 1961-670, sited
on this soil overlying moderately fractured metamorphic rock,
showed that maximum changes in ground water storage were about
25 mm (1 in) in any two consecutive years of observation;
maximum changes in ground water discharge amounted to no more
than 130 mm (5 in). The magnitude of these changes was
strongly dependent on variations in rainfall from one year to
the next. These relationships probably apply to bedrock areas of
the study region in an approximate way. In alluviated valley
areas, however, it is expected that ASMS and AGWS are signifi-
cantly greater, because infiltration rates and soil thickness
are considerably greater than in bedrock areas.
3.5 CHEMICAL CHARACTERISTICS OF GROUNDWATER
The quality of ground and surface waters in this region is
generally quite good, except that certain ground and surface
waters in Clear Lake (Cache Creek) Basin are high in boron as a
result of recent volcanic activity. Boron in concentrations
greater than about 1 ppm is injurious to many plant species. In
Clear Lake, boron is 1-4 ppm, and in Borax Lake about about 590
ppm. The chemical characteristics of ground water and water
quality are discussed below by individual drainage basin.
Big Valley—
Quality of both ground and surface waters in Big Valley is
generally very good. TDS average about 4 ppm in surface waters
and 500 ppm in ground waters. Boron in ground waters generally
is under 0.3 ppm, but reaches concentrations between 0.7 and 2.5
ppm in several wells.
High Valley—
Water quality data is not available for High Valley; how-
ever, the water is suitable for domestic and agricultural pur-
poses .
Valley East of Clearlake Oaks—
A few wells in the western part of the valley supply ade-
quate water for domestic use; no irrigation wells exist.
The quality of the ground water is poor, and several wells
in the western portion of the valley were destroyed because the
water had a very unpleasant taste. One well in the eastern part
is reported to have high soda and iron content.
At the south edge of the valley east of Clearlake Oaks lies
the Sulphur Bank Mine, where sulphur and great quanta.tites of
quicksilver were mined. Thermal spring waters in this area are
highly charged with minerals and gases. As reported by Roberson
and Whitehead (1961), these waters are rich in ammonia and
nitrogen (up to 485 ppm, as NH4+), nitrate (up to 470 ppm),
191
-------
bicarbonate (up to 4,000 ppm), sulfate (up to 4,900 ppm) and
chloride (up to 869 ppm); hydrogen sulfide reaches about 10 ppm
in two springs. Their analyses did not include cations.
Ecoview Environmental Consultants (1976) reported the chemistry
of one spring above Sulphur Bank Mine, which showed the follow-
ing cation concentrations (in ppm): calcium = 235; magnesium =
200; sodium = 780; potassium = 26; boron = 50. Anion and gases
were of the order reported by Roberson and Whitehead (1961).
In view of this highly charged thermal water at Sulphur
Bank, it is not surprising that cool ground waters in the adja-
cent valley are also heavily mineralized; probably this occurs
by leakage along faults and subsequent mixing with shallow,
relatively pure water.
Borax Lake Basin—
Several wells are located on the low volcanic hill between
Borax Lake and Burns Valley. Apparently this ground water is of
acceptable quality for domestic and orchard irrigation use.
No wells are located in the alluvium bordering Borax Lake.
However, it can be predicted that ground water there is highly
mineralized, especially in boron. The waters and muds of Borax
Lake are extremely alkaline, saline and borated and were once
mined for borax. It appears that the source of the borax was
borated solfataras or springs that issued from the bottom of the
lake. Probably, these had the same volcanic source as springs
at Sulphur Bank, about 1.5 km (1 mi) to the north.
Burns Valley—
Except for a narrow strip along the lakeshore, the ground
water of Burns Valley is of good quality. Chloride and hardness
and conductance were determined as 7 and 63 ppm and 263 micro-
mhos, respectively, in a well about 0.8 km (0.5 mi) from the
lake.
Small Flats South of Mount Konocti—
No water quality data is available for the four small flats
south of Mount Konocti.
Collayomi Valley—
Partial analyses of water show that chloride and hardness
are about 4 and 150 ppm, respectively. All water in the valley
appears suitable for domestic and agricultural use (Upson and
Kunkel, 1955).
Alexander Valley—
Chemically, ground water in Alexander Valley generally is
of the hard, bicarbonate type. Hardness (as calcium carbonate
[CaC03]) ranges from 80 to 1,300 ppm; TDS range up to 1,300 ppm;
boron varies from 0 to 40 ppm (Cardwell, 1965) but is usually
under 0.5 ppm. Overall, the water is adequate for irrigation
but requires softening for domestic use.
192
-------
Upper Napa Valley—
Water quality data is limited for the Calistoga area TDS
throughout Napa Valley average about 200 to 700 ppm. TDS are
not given by Kunkel and Upson (1960) for the Calistoga area but
chloride there is given as 190 ppm; this suggests that TDS may
range to nearly 1,000 ppm.
Mayacmas Mountains—
Ground water quality information is unavailable for the
Mayacmas Mountains.
Excelsior Valley—
Ground water quality data is very sparse for this basin.
TDS in ground water occurring in the Excelsior Valley may
average 150 to 300 ppm.
3.6 SEISMICITY
This section presents, in general terms, the historical
seismicity, microseismicity and seismic risk in The Geysers-
Clear Lake region.
3.6.1 Historical Seismicity
Figure 3.3 shows earthquake epicenters as located by the
Seismograph Station at the University of California, Berkeley
(U.C.B.), for the period 1910-76. Currently the accuracy of
U.C. epicenters in this area is probably better than ± 5 km (3
mi) for magnitude 3.5 or greater shocks; however, before 1963,
when the U.C. seismograph network was greatly improved, accuracy
probably improved from about ±20 km (12 mi) in 1910 to ±10 km (6
mi) in 1962 (McEvilly, pers. comm., 1974). For this reason, one
cannot see distinct clustering of U.C. epicenters along the
.active Rodgers Creek-Healdsburg Fault System, nor along any
other faults.
Historical Seismicity and Earthquake Damage—
Since 1855, more than 140 earthquakes have been felt in the
Santa Rosa-Sonoma Valley-Clear Lake region. While some ten of
these did significant damage in Santa Rosa and Sonoma Valleys,
only one was destructive in the study region itself. This was
the great 1906 (M = 8.25 earthquake, caused by rupture along the
San Andreas Fault; the break extended from San Juan Bautista on
the south to Point Arena, or perhaps Shelter Cover, on the
north, a distance of at least 300 km (190 mi); along its reach
through Sonoma and Mendocino Counties, strike-slip displacement
averaged about 4.5 m (15 ft). Damage to buildings in Santa Rosa
Valley varied from nil to major. In the following, it is impor-
tant to keep in mind that intensity values are qualitative in
nature and combine effects of both vibratory and permanent
ground motions. Modified Mercalli (MM) intensity (Table 3.3)
193
-------
I23°30'
39°30'
o O
I23°00'
+
I22°30'
o
o
o o
o
I22°00'
x» O o — —
DO I
6>
o x
O CO
O
o
39°00'
EXPLANATION
SYMBOL MAGNITUDE
O >6.0
D 5.0 10 5.9
O 4.0 10 4.9
o 3.0 to 3.9
o <2.9
x NO RECORDED
MAGNITUDE
cf
H-
PACIFIC OCEAN
3B°00'
> OOOC
co O
THE GEYSERS
o oSEOTHERMAL FIELD
O C?
o o o o
o o o o
X OUO O80 O C O
B o o o°o ° c
o c
20 c
o o
Figure 3.3 Earthquake epicenters located by the University of
California, Berkeley, 1910-76.
194
-------
TABLE 3.3 MODIFIED MERCALLI INTENSITY SCALE
(ABRIDGED)
I. Not felt except by a very few under
specially favorable circumstances. (I
Rossi-Forel scale.) VIII.
II. Felt only by a few persons at rest, espe-
cially on upper floors of buildings.
Delicately suspended objects may
swing. (I to II Rossi-Forel scale.)
III. Felt quite noticeably indoors, especially
on upper floors of buildings, but many
people do not recognize it as an earth-
cruake. Standing motorcars may rock
slightly. Vibration like passing of
truck. Duration estimated. (Ill
Rossi-Forel scale.)
IV. During the day felt indoors by many, IX.
outdoors by few. At night some
awakened. Dishes, windows, doors
disturbed; walls make creaking sound.
Sensation like heavy truck striking
building. Standing motorcars rocked
noticeably. (IV to V Rossi-Forel
scale.)
V. Felt by nearly everyone, many awak- X.
ened. Some dishes, windows, etc.,
broken; a few instances of cracked
plaster; unstable objects overturned.
Disturbances of trees, poles, and other
tall objects sometimes noticed. Pen-
dulum clocks may stop. (V to VI
Rossi-Forel scale.)
VI. Felt by all, many frightened and run XI.
outdoors. Some heavy furniture
moved; a few instances of fallen plas-
ter or damaged chimneys. Damage
slight. (VI to VII Rossi-Forel scale.)
VII. Everybody runs outdoors. Damage neg-
ligible in buildings of good design and XII.
construction; slight to moderate in
well-built ordinary structures; consid-
erable in poorly built or badly de-
signed structures; some chimneys
broken. Noticed by persons driving
motorcars. (VIII Rossi-Forel scale.)
Damage slight in specially designed
structures; considerable in ordinary
substantial buildings with partial col-
lapse; great in poorly built structures.
Panel walls thrown out of frame
structures. Fall of chimneys, factory
stacks, columns, monuments, walls.
Heavy furniture overturned. Sand
and mud ejected in small amounts.
Changes in well water. Persons driv-
ing motorcars disturbed. (VIII+ to
IX— Rossi-Forel scale.)
Damage considerable in specially de-
signed structures; well-designed frame
structures thrown out of plumb; great
in substantial buildings, with partial
collapse. Buildings shifted off founda-
tions. Ground cracked conspicuously.
Underground pipes broken. (IX+
Rossi-Forel scale.)
Some well-built wooden structures de-
stroyed; most masonry and frame
structures destroyed with foundations;
ground badly cracked. Rails bent.
Landslides considerable from river-
banks and steep slopes. Shifted sand
and mud. Water splashed (slopped)
over banks. (X Rossi-Forel scale.)
Few, if any, (masonry) structures re-
main standing. Bridges destroyed.
Broad fissures in ground. Under-
ground pipelines, completely out of
service. Earth slumps and land slips
in soft ground. Rails bent greatly.
Damage total. Waves seen on ground
surfaces. Lines of sight and level
distorted. Objects thrown upward into
air.
195
-------
ranged from about VII to IX in the valley, reaching IX in the
city of Santa Rosa due to soft, saturated ground conditions
there. The ground was extensively fissured in Santa Rosa,
probably as a result of lurching and differential settlement;
some liquefaction may have occurred. In the Mayacmas Mountains,
MM intensity was about VI to VII, with very minor damage
reported from The Geysers; intensity VII characterized Sonoma
Valley. Around Clear Lake, damage was confined to alluviated
areas along the north and west shores: MM intensity VII pre-
vailed in the area from Kelseyville to Upper Lake, as evidenced
by fallen chimneys; fissures were reported in alluvial ground
south of Kelseyville. Detailed information on damage caused by
the 1906 earthquake may be found in Lawson, et al. (1908).
Two of the three most important factors controlling earth-
quake damage versus magnitude, fault distance and ground consol-
idation were well-exemplified in the 1906 earthquake. For
constant distance from the fault rupture, damage to a given type
of structure was controlled by shallow ground conditions, being
minimal on bedrock and maximal on water-saturated unconsolidated
alluvium; for given ground conditions, damage varied inversely
with epicentral distance.
Other than the 1906 event, no shock in the region has been
of sufficient magnitude to cause significant damage in the study
area. The largest had magnitudes estimated to have been near 5,
and produced MM intensity VII (fallen chimneys) at Upper Lake
and along the Russian River from Healdsburg to Ukiah; these
places are located near the margins of the study area and on
alluvium. However, maximum MM intensity within the study area
probably did not exceed VI on alluvium and V on bedrock.
In 1969 two earthquakes, with magnitudes 5.6 and 5.7,
occurred on the southern end of the Healdsburg Fault, on the
north side of Santa Rosa. They caused substantial damage to
buildings in Santa Rosa but not within the study area.
3.6.2 Microseismicity
The Geysers geothermal field is characterized by high
microseismicity (Bufe, et al./ 1976). Most microearthquakes
there have had magnitudes less than 2 and focal depths in the
range of 2.6 to 6.0 km (1.6 to 3.75 mi). It is widely accepted
that this prolific, shallow microseismicity is caused by in-
creased temperature and pore pressure of water within the geo-
thermal reservoir. This condition weakens the rocks to such an
extent that regional strain is released continuously by small-
displacement fault-rupture events in the geothermal field. Such
activity serves to help maintain the system of open fractures
necessary to create most geothermal reservoirs.
196
-------
Teleseismic residuals in the area have been analyzed by
Iyer (1975). He found that positive residuals of about 0.5
second characterize ray paths near the margin of the gravity
anomaly; these increase to 1.5 second for rays penetrating the
anomaly's center. This is believed to be strong evidence for
the existence of a magma chamber.
Immediately following the Santa Rosa earthquakes in 1969,
the National Center for Earthquake Research (NCER) of the USGS
extended its dense Bay Area seismograph network into the Santa
Rosa Valley area. Plate 3.2 shows NCER epicenters and stations
in the area from 38°30' to 39° N latitude and 122° to 123° W
longitude for the period 1969-76 (Bufe, et al., 1976) and a
correlation between epicenters and the mapped traces of the
Rodgers Creek-Healdsburg Fault Systems. This correlation
appears because of the relatively high accuracy and precision of
the NCER data: most epicenters are accurate to better than ±1 km
(0.6 mi). An updated version of this map, with more accurate
epicenter locations, will be released by the USGS by the end of
1977. Most of the epicenters at the southern end of the Healds-
burg Fault are aftershocks of the 1969 Santa Rosa earthquakes.
Both the USGS and U.C.B. data indicate a lack of seismicity
along the San Andreas Fault; this is characteristic of the fault
northward from the Santa Cruz Mountains to Point Arena. It may
also be seen that there is very little seismicity west of the
Rodgers Creek-Healdsburg Fault but a great deal to the east.
This could be a result of the 1906 earthquake, which probably
released most of the stored crustal strain energy in the west-
ern part of the map area. Crustal strain apparently is still
low there, but geodetic measurements at Fort Ross and Point
Reyes (Greensfelder, 1972, p. 9) indicate that strain is now
accumulating along the San Andreas Fault.
The NCER data show high microseismicity in The Geysers
geothermal field, but epicenter locations do not resolve speci-
fic active faults. It seems safe to say that seismicity there
is produced by microfracturing throughout the geothermal field.
This is probably the result of low-level strain release which is
localized by high temperature and pore pressure in the geo-
thermal system. To the east, in the Clear Lake area, microseis-
micity is much lower than in The Geysers area. Nearly one-half
of all microearthquakes in this area occurred in a two-day-long
swarm located under the south flank of Mount Konocti, and one
mile west of the trace of the Konocti Bay Fault. All of these
shocks had a similar focal mechanism, with modal planes paral-
leling the fault, and the shocks may have occurred on the fault
(Bufe, pers. comm., 1976). Therefore, we conclude that the
Konocti Bay Fault is seismically active. Otherwise, epicentral
data do not delineate faults in the Clear Lake area.
197
-------
3.6.3 Seismic Risk
Seismic risk is the likelihood of damage from an earth-
quake. This hazard is comprised of two distinct classes of
ground movement—vibrational and permanent. The degree of these
hazards varies geographically as a function of seismic potential
and near-surface geologic conditions. Seismic risk, i.e., the
probability of property loss or human injury, is a function of
naturally occurring seismic hazards and the earthquake resist-
ance of the works of man. Where there are no man-made struc-
tures, seismic risk is small. Evaluation of seismic risk means
estimation of all of the following: the location, magnitude and
frequency of earthquakes; vibratory motion in rock; the response
of unconsolidated earth materials to these rock motions; and the
response of man-made structures to resultant ground surface
motions. The disciplines of seismology, geology, soils and
structural engineering must all be used, and expert practition-
ers in each of these fields will admit to significant uncer-
tainties in prediction of the phenomena with which they deal.
Seismic risk elements discussed in this section are inten-
sity, occurrence, vibratory rock and ground motion, and perman-
ent ground motions including faulting, liquefaction, landslid-
ing, differential settlement and lurch-cracking. These elements
are not specified in sufficient detail for aseismic engineering
of structures at specific sites. However, all important risk
factors are presented and should form adequate guidelines for
detailed, site-specific analyses.
Intensity Recurrence—
Figure 3.4 is a graph showing the historic frequency of
occurrence of earthquake intensities (MM) in the Santa Rosa
Valley area, as well as for the entire San Francisco Bay region.
Due to their historically sparse populations, the Mayacmas
Mountains and Lower Lake-Middletown areas do not afford adequate
reporting of intensities. However, the distribution of epicen-
ters and the predominance of bedrock as foundation materials in
the study region assured that the curves of Figure 3.4 represent
upper bounds for intensity recurrence there.
The data used to construct the curves covers the period
1810-1966 for the entire Bay region, and 1855-1966 in Santa Rosa
Valley (Algermissen, et al., 1969, p. 37-42). It can be seen
that the frequency of occurrence of strong ground shaking
(intensities VI, VII, and VIII) has been nearly as great in
Santa Rosa Valley as in the entire San Francisco Bay region.
Note that extending the data base up to the present; thus,
including the 1969 Santa Rosa earthquakes of intensity VII-VI11
would bring the two curves even closer together.
198
-------
Santa Rosa Valley Area
1855-1966
0 San Francisco Bay Region
1810-1966
V VI VII VIII
MODIFIED MERCALLI INTENSITY
Figure 3.4
Frequency of occurrence of earthquake intensities,
Santa Rosa Valley region.
(data from Algermissen, et al./ 1969)
199
-------
If the last 160 years are fairly representative of long-
term seismicity of the Bay region, then it seems we should
expect potentially damaging ground shaking (intensity VII or
greater) about once every 30 years, on the average, in alluvi-
ated portions of the study region. On bedrock within the study
region, the "30-year intensity" is probably about VI; intensity
VII or greater may be expected about once every century; and
intensity VIII, which may be damaging to modern structures, no
more than about once in 3 centuries.
Magnitude versus Frequency of Occurrence--
In order to make a more refined, quantitative assessment of
maximum probable ground shaking, it is necessary to analyze
magnitude versus frequency of occurrence of earthquakes. As
described below, definition of the true or long-term average
magnitude equal frequency characteristic of this region is not a
simple matter. This is because the historic seismicity record
is short relative to long-term variations of regional crustal
strain, and because instrumental magnitudes are available only
since 1932.
The greater San Francisco Bay region, extending from Monte-
rey Bay on the south to Ukiah on the north, and east to Vaca-
ville, is one of the most seismically active areas of Cali-
fornia. Seismicity was much higher in this region during the
nineteenth century than it has been in the twentieth: since the
great 1906 earthquake, a few moderate (magnitude less than 6.0)
and no major shocks have occurred; however, between 1836 and
1906 there were 5 major (magnitude probably greater than 7.0),
and a number of moderate shocks. The following analysis of
magnitude versus frequency of occurrence demonstrates and inter-
prets this temporal change in seismicity.
Figure 3.5 shows relationships between earthquake magnitude
and frequency of occurrence for two regions: the entire central
California Coast Range area, and the area covered by the Santa
Rosa Sheet (Koenig, 1963) bounded by 38° to 39° N latitude and
122° and 124° W longitude, including all of Sonoma and Napa
Counties and portions of five others. Two curves are shown for
the central Coast Range area, one for the period 1810 to 1931,
and another for the period 1932 to 1961. These curves are based
on the work of Ryall, et al. (1966, p. 1124), who estimated
magnitudes of most pre-1932 earthquakes from intensity data.
The seismicity of this region is stated in terms of a 19,000
sq km (7,500 sq mi) area of the Santa Rosa Sheet. For the Santa
Rosa Sheet, there is one curve covering the period 1944 to 1971,
as magnitude data for pre-1944 earthquakes is unavailable. Data
for the area covered by the Santa Rosa Sheet (Koenig, 1963) is
from the University of California (1977), whose earthquake
records begin in 1910; Figure 3.5 is a plot of U.C.B. epicenter
data for the area from 38° to 39° 30' N latitude and 122° to
123° 30' W longitude for the interval 1910 to 1976. Table 3.4
200
-------
From Ryall etal, 1966
6 7
MAGNITUDE
Figure 3.5 Magnitude versus frequency of occurrence for
earthquakes in the central Coast Range.
201
-------
TABLE 3. 4 EARTHQUAKE RECURRENCE DATA FOP THE CENTRAL COA.ST RANGE REGION
Earthquake n.nta Set
Region Area (km^) Period (years)
Santa Rosa Sheet 12,000 1944-1971
Central Coast 33,000 1932-1961
Ranges
Central Coast
Ranges 37,000 1810-1931
Recurrence
Parameters
a h
1.42 0.72
2.83 0.90
s
0.84 0.53
Avcrap.c Recurrc
1,000 km2
M: 6 7
720 3600
370 2960
216 735
nee Intervals (yrs)
12,000 km2
678
60 300 1500
32 250 2000
IS 62 21D
Parameters of the equation log N = a-b M;
'a' is normalized on an annual and per 1000 km basis.
For the Central Coast Ranges, 'a' and 'b' are from Ryall et al, 1966, p. 1124,
O
NJ
-------
presents the data of Figure 3.5 in numerical form, as well as
average recurrence intervals for magnitudes 6, 7, and 8.
The region covered by the Santa Rosa Sheet was chosen for
analysis because it is both convenient and large enough to
afford a fair sample of seismicity important to the study area.
The reliability of magnitude-frequency curves as indicators of
future seismicity is proportional to the time-area sample of
past seismicity used to prepare them. There is good reason to
believe that the 28-year record (1944-71) of the Santa Rosa
Sheet area, as well as the 30-year record (1932-61) of the
central Coast Range, is a poor index of future seismicity. This
is because the 1906 earthquake released nearly all the accum-
ulated strain in the central Coast Range area; thus seismicity
has been abnormally low since 1906. On the other hand, it could
be argued that seismicity was abnormally high in the 100- year
period immediately preceding the 1906 event due to an unusually
high level of strain. Long-term average seismicity for the
region probably falls in between that of the pre- and post-1906
periods.
Table 3.4 and Figure 3.5 show that, for the period 1932 to
1971, seismicity (per unit area) of the Santa Rosa Sheet is
similar to that of the larger central Coast Range zone for
magnitudes 6 and greater. Therefore, the long-term unit-area
seismicity of the two regions should be similar, and we believe
that the recurrence intervals for the central Coast Range for
1810-1931 are a reasonably good indicator of future seismicity
affecting the study region. Geodetic and geologic data bearing
on the long-term displacement rate along the San Andreas Fault
suggest a recurrence interval of from 100 to 400 years for
magnitude 8 or greater earthquakes at any place along the fault
(Wallace, 1970). This is in satisfactory agreement with the
seismicity data.
Vibratory Ground Motion—
Previously, it was concluded that potentially damaging
ground shaking may recur at an average rate of about once every
30 years on alluvial ground. This is a very crude estimate of
the frequency of occurrence of damaging ground motions.
Although there is insufficient data to define the character of
future ground shaking in alluviated areas, we are able to des-
cribe with some confidence the characterisitcs of seismic ground
motion on bedrock.
In addition, we can predict the gross geographic distribu-
tion of permanent (not vibrational) ground movements: liquefac-
tion, lurch-cracks and differential settlement occur only in
alluvial areas, and landsliding only in hilly areas.
203
-------
Maximum Bedrock Acceleration--
Maximum shaking in rock is commonly specified in terms of
maximum credible and maximum probable accelerations. Maximum
credible acceleration at any given place is defined as the
maximum acceleration that could reasonably be expected to occur,
given the known geologic framework. Thus it is based entirely
on the location, length and relative recency of faults in the
region surrounding a site under consideration. Maximum probable
acceleration at a site is derived from statistical analysis of
the recorded seismicity of the surrounding region.
Shaking is not completely described by maximum accelera-
tion, above> one also needs to know its duration and spectral
character, i.e., the distribution of amplitude relative to
vibrational period. Spectral shapes appropriate for rock can be
computed and scaled to fit maximum acceleration values from
existing accelerograms. As an additional matter, rock acceler-
ations may be modified by topography, but this is not well
understood; in the 1971 San Fernando earthquake, shattered
overturned soil was frequently noted on ridge tops.
For most engineering work, it is both realistic and prac-
tical to use maximum probable acceleration in regions where the
spatial and temporal distribution of destructive earthquakes is
not well understood. Of course, most areas fall into this
category, the present one included. In other words, where
seismicity is largely known in a statistical (not deterministic)
way, it is sensible to predict ground motion in a probablistic
manner.
Maximum Credible Acceleration—
Only three major (more than a few kilometers in length)
active faults are known to lie within 50 km (31 mi) of the study
region; faulting beyond this distance is not capable of produc-
ing significant damage. The three faults are, from west to
east, the San Andreas, Healdsburg-Rodgers Creek and Maacmas
Faults. The first two are proven seismically active; the
Maacmas Fault appears to creep (aseismic slippage), but no
earthquakes are known to have occurred on it. In addition,
there is speculation that the Collayomi Fault may be active, but
there is little evidence for this. Other, shorter faults may be
active or potentially active, particularly some in The Geysers-
Clear Lake region. However, except for the Konocti Bay Fault,
there is no clear evidence for their activity. At an arbitrary
location, accelerations induced by earthquakes on shorter
faults, many of which are unknown, may exceed those from events
on major faults.
Maximum credible bedrock acceleration may be estimated from
the length of and distance from a given fault. Empirical data
(Bonilla, 1970) relates rupture length and magnitude. Assuming
that the entire mapped length of an active fault may rupture
204
-------
during a single event, one can estimate the maximum credible
magnitude of earthquakes on particular faults. In this way, we
estimate 8.5 on the San Andreas, 7.5 on the Healdsburg-Rodgers
Creek and 6.5 on the Maacmas Fault. From empirical curves
relating peak rock acceleration, earthquake magnitude and dis-
tance from the causative fault (Schnabel and Seed, 1973), we
find that maximum credible bedrock acceleration in the study
region varies from about 0.7 g adjacent to active faults down to
about 0.2 g south of Lower Lake.
Duration of strong shaking for these maximum credible
events varies from about 20 seconds for M = 6.5 to 40 seconds for
M = o • b .
Maximum Probable Acceleration—
Maximum probable acceration may be derived using seismicity
models of varying sophistication. The most sophisticated type
involves both known fault sources and random sources of earth-
quakes. It requires that regional seismicity be apportioned
among known active faults and unknown or unmapped faults which
must be assumed to have a random distribution. Such an analysis
would be useful for the study area; however, it is beyond the
scope of this report.
A much simpler technique simply assumes that all earth-
quakes are randomly distributed, implicitly on unknown faults.
According to the method of Cornell (1968), and using magnitude-
frequency parameters for 1810-1930 in the central Coast Range
(see Table 3.4), maximum probable bedrock acceleration per 100
years is about 0.26 g in this area. This has a 63% chance of
being exceeded in any 100-year interval, or 30% in 50 years.
Design to this value would not be "conservative," in the engi-
neering sense of the term.
A more conservative design might use the 200-year maximum
probable bedrock acceleration, with a 30% chance of being
exceeded in any 100-year interval (or 15% in 50 years); this is
0.42 g.
However, we expect most of the larger earthquakes to be
associated with the Healdsburg or San Andreas Faults, located
beyond the region of expected geothermal development. Therefore,
the accelerations given above are really too high for the given
time periods, but by an unknown amount. A more sophisticated
analysis, as outlined above, would certainly give smaller values
of acceleration in the area of concern.
Permanent Ground Deformation—
Liquefaction,differential settlement, lurch-cracking,
surface faulting and landsliding comprise the various types of
permanent ground deformation, or ground failure. All but fault-
ing result from ground shaking; faulting is the proximate cause
205
-------
of ground shaking. Strictly speaking, liquefaction is a cause,
rather than a manifestation, of ground failure.
Although permanent ground deformations may locally do
serious damage to building foundations, ground shaking will
cause more widespread and greater total depth of deformation.
Liquefaction and its Effects—
Liquefaction is defined as the transformation of a granular
material from a solid into a liquefied state as a consequence of
increased pore-water pressures. It is a common occurrence in
water-saturated sandy deposits subjected to strong earthquake
shaking, and is the proximate cause of low angle flow and late-
ral spreading landslides, lurch-cracking and "quick condition"
failures. Liquefaction may be an important problem where the
ground water table in alluvial areas is generally not more than
3 to 6 m (10 to 20 ft) deep. It may also occur in water-satu-
rated fills, such as are often constructed for drilling pads and
power plant facilities in the Mayacmas Mountains. During the
1906 earthquake, liquefaction apparently occurred near the Santa
Rosa cemetery and at Altruria where water ejection (reported
formation of springs) was noted in connection with ground dis-
turbances; in Santa Rosa itself, liquefaction apparently did not
take place. During the 1969 earthquakes, liquefaction may have
been involved in the ground failures that damaged pipes, streets
and curbs. Youd (1973) has described the mechanics and effects
of liquefaction in some detail, which we need not repeat here.
However, a brief description of effects is given below.
Flow Landslides—
These result when mobilized soil is unrestrained, and large
masses of earth materials may travel long distances in the form
of liquefied flows or blocks of intact materials riding on
liquefied materials. In the 1906 earthquake, one such slide
occurred at the base of San Bruno Mountain on the San Francisco
Peninsula, flowing several hundred yards on a slope of about
Lateral Spreading Landslides--
These are probably much more common than the above type
and involve smaller displacements. Youd (1973) uses the term to
denote all limited-displacement ground failures associated with
liquefaction, including lurch-cracks. Repeated episodes of
limited flow may occur during a strong earthquake, resulting in
a large total displacement; they are most probable on gentle
slopes, having angles of the order of l% to 2%. Such landslides
are common in moderate and strong earthquakes and were the
cause of extensive damage in the San Fernando earthquake of
1971.
206
-------
Quick Condition Failure—
Seeping forces,caused by upward percolating pore water,
often reduce the strength of granular soils to a point of insta-
bility, which is termed a "quick condition." This condition is
usually limited to thick sand layers extending from below the
water table to the surface. Loss of bearing capacity is the
most common effect of a quick condition; buoyant rise of buried
tanks is also common. In the 1964 Niigata, Japan, earthquake,
several high-rise apartment buildings rotated and sank into
liquefied soil.
Differential Settlement—
This can be quite severe in man-made fills but may also
occur in natural ground. Liquefaction may be a factor in caus-
ing differential settlement.
Landsliding and Faulting—
Landslides and land slumps are frequently triggered by
strong ground shaking. In the Mayacmas Mountains extensive
areas are underlain by melange deposits of the Franciscan
Formation which are particularly prone to landsliding, even
without earthquake shaking.
The Study Area—
Much of the Franciscan Formation, particularly the melange
deposits, is subject to landsliding under aseismic conditions.
Of course, these same areas are subject to additional landslide
potential under earthquake loading. Therefore, slope stability
studies for siting geothermal facilities should include analysis
of the effect of earthquake shaking.
Failure by liquefaction may be a problem in saturated
alluvium or fills which contain much silt- to sand-sized mate-
rial. Good drainage may practically eliminate potential problems
in such fills.
207
-------
REFERENCES
Algermissen, S. T., J. C. Stepp, W. A. Rinehart and E. P.
Arnold. Studies in Seismicity and Damage Statistics,
Appendix B. U.S. Department of Commerce, Environmental
Science Services Administration, Coast and Geodetic Survey,
68 p., 1969.
Bonilla, M. G. Surface Faulting and Related Effects; in Earth-
quake Engineering, R. L. Wiegel, Principal Investigator,
Prentice Hall, New Jersey, p. 4774, 1970.
Brice, J. E. Geology of the Lower Lake Quadrangle, California.
Cal. Div. Mines and Geol. Bull. 166, 1953.
Bufe, C. G. , J. H. Pfluke, F. W. Lester and S. M. Marks. Map
Showing Preliminary Hypocenters of Earthquakes in the
Healdsburg Quadrangle, Lake Berryessa to Clear Lake, Cali-
fornia, January 1969-June 1976. USGS, Open File Report
76-8021, 1976.
California Department of Water Resources. Lake County Investi-
gation. Bull. 14, 1957.
Evaporation from Water Surfaces in California.
Bull. 73-1, 1974.
Vegetative Water Use in California, 1974. Bull.
113-3, 1975.
Cardwell, G. T. Geology and Ground Water in Russian River
Valley and in Round, Laytonville and Little Lake Valleys,
Sonoma and Mendocino Counties, California. USGS Water
Supply Paper 1548, 154 p., 1965.
Cornell, C. A. Engineering Seismic Risk Analysis. Bull. Seism.
Soc. Am., v. 58, p. 1583-1606, 1968.
Ecoview Environmental Consultants. Borax Lake Study Area, Lake
County, California Consulting Report for Philips Petroleum
Company, 1976.
Greensfelder, R. W. Crustal Movement Investigation in Cali-
fornia. Cal. Div. Mines and Geol., Special Publication 37,
1972.
208
-------
Hearn, B. C.,Jr., J. M. Donnelly and F. E. Goff. Preliminary
Geologic Map of the Clear Lake Volcanic Field, Lake County
California. USGS Open File Report 75-391, 1975.
Iyer, H. M. Teleseismic Residuals at The Geysers Geothermal
Area. Trans. Am. Geophys. Un., v. 56, p. 1020, 1975.
Koenig, J. Geologic Map of California, Santa Rosa Sheet. Cal.
Div. of Mines and Geol., 1963.
Kunkel, F.,and J. E. Upson. Geology and Ground Water in Napa
and Sonoma Valley, Napa and Sonoma Counties, California.
USGS Water Supply Paper 1495, 1960.
Lawson, A. C., et al. Report of the State Earthquake Investi-
gation Commission. Carnegie Inst., Wash., 1908.
Lewis, D. C.,and R. H. Burgy. Water Use by Native Vegetation
and Hydrologic Studies. Dept. of Water Science and Engi-
neering, University of California, Davis, Annual Reports
No. 2-7, 1961-67.
McLaughlin, R. J. Preliminary Geologic Map of The Geysers Steam
Field and Vicinity, Sonoma County, California. USGS Open
File Map 74-238, 1974.
Mooney, M. L. Mendocino Transmission Line Study, Cloverdale
Peak, The Geysers, and Mt. Vaca. Pacific Gas and Electric
Co., Meteorological Office, 1975.
National Oceanic and Atmospheric Administration. Climatological
Data, Annual Summary, California. v. 79, No. 13, 1975.
Roberson, C. E., and H. C. Whitehead. Ammoniated Thermal Waters
of Lake and Colusa Counties, California. USGS Water Supply
Paper 1535-A, 1961.
Ryall, A., D. B. Slemmons and L. D. Gedney. Seismicity, Tecton-
ism, and Surface Faulting in the Western United States.
Bull. Seis. Soc. Am., v. 63, p. 1105-1135, 1966.
Schnabel, p. B., and H. B. Seed. Accelerations in Rock for
Earthquakes in the Western United States. Bull. Seis. Soc.
Am., v. 63, p. 501-516, 1973.
Soil Mechanics and Foundation Engineers, Inc. Big Valley Ground
Water Recharge Investigation. Consulting Report for Lake
County Flood Control and Water Conservation District, 1967.
209
-------
Swe, W., and W. R. Dickinson. Sedimentation and Thrusting of
Late Mesozoic Rocks in the Coast Ranges near Clear Lake,
California, Bull. Geol. Soc. Am., v. 81, p. 165-188, 1970.
University of California. Bull, of Seismographic Stations
(Geonomics plot from magnetic tape), 1977.
Upson, J. E., and F. Kunkel. Ground Water of the Lower Lake-
Middletown Area, Lake County, California. USGS Water
Supply Paper 1297, 1955.
U. S. Department of the Interior. Final Environmental Statement
for the Geothermal Leasing Program, Vol. II of IV, 1973.
U. S. Geological Survey. Surface Water Supply of the United
States, 1966-1970, Part II, Pacific Slope Basins in Cali-
fornia. USGS Water Supply Papers 2129 and 2131, 1976.
Wallace, R. E. Earthquake Recurrence Intervals on the San
Andreas Fault. Bull. Geol. Soc. Am. v. 81, p. 2875-2890,
1970.
Youd, L. T. Liquefaction, Flow and Associated Ground Failure.
USGS Circular 688, 1973.
210
-------
SECTION 4
KLAMATH FALLS
4.1 INTRODUCTION
This section presents baseline data on climatology,
geology, hydrology and seismology to aid in assessment of envi-
ronmental impacts of potential geothermal development in Klamath
Falls, Oregon. Descriptions of aspects of climatology, geo-
thermal characteristics, tectonic history, faults, stratigraphy,
lithology and surface water that are related to and influence
the ground water regime are discussed, as well as ground water
systems and the chemical characteristics of ground water. A
brief section on the extremely low seismicity of the area is
included.
4.1.1 Summary
Klamath Falls, in south-central Oregon, is within a long,
northwest trending structural depression, the Klamath Basin
(Fig. 4.1). At Klamath Falls City, some 300 shallow wells,
generally less than 150 m (500 ft) in depth, tap thermal aqui-
fers at temperatures to more than 104°C (220°F). Water from
these wells is used for space heating in homes, schools and
numerous commercial buildings. Other, presumably smaller,
thermal anomalies are present at Klamath Hills, Olene and else-
where in the Klamath Basin. All appear to be fault-controlled,
and to store hot water in rubbly, fractured basalt aquifers.
Surface waters are dominated chemically by calcium, magnes-
ium and bicarbonate; deeper thermal waters are principally
sodium chloride and sulfate chloride in composition. As there
is no data from wells deeper than 600 m (2,000 ft) the nature of
a deep circulation system is problematic.
4.1.2 Background
Location—
The area under discussion here covers the central and
southern parts of the Klamath Basin topographic and geologic
area, located in Klamath County, southwestern Oregon (Fig. 4.1).
Most geothermal anomalies and all of those likely to undergo
development lie between latitudes 42° 30'N and 42° 00'N. West-
ward the area extends to the foothills of the Cascade Range, and
eastward, to a line of ridges extending through Naylox Mountain,
211
-------
124°
46°
HI23<
H.
122° 121
120° 119° 118°
43C
42°-
PORTLAND
NDL. J ^''*~''
SALEM *
IEUGENE*
BEND
LA
GRANDE
•
I
117° '
I
•c46'
"\
BAKER • /!
(' '
•43°
124° |23° 122° 121° 120° 119° 118° H7°
42
Figure 4.1 Location map of the Klamath Basin study area.
212
-------
Hogback Mountain and Stukel Mountain. While most of the follow-
ing discussion focuses on this area, data from the surrounding
region is presented whenever it is necessary for an understand-
ing of the geothermal resource.
The Klamath Basin region is covered by U.S. Army Map Ser-
vice sheets at a scale of 1:250,000. The area of study is also
covered by recent USGS topographic quadrangle maps at a scale of
1:62,500.
Method of Study—
This study is based on a compilation of published and
unpublished data. Much of the information contained in this
report has been obtained from unpublished materials. The chief
sources of this type of data have been the Oregon State Engineer
(ground water records), State of Oregon Department of Geology
and Mineral Industries (geologic mapping and geothermal develop-
ment data), Oregon Institute of Technology (OIT) at Klamath
Falls (local geothermal development data) and the Weyerhaeuser
Corporation (detailed geologic mapping).
Previous Work—
Several reconnaissance and detailed studies of various
aspects of the geology, hydrology and geothermal resource devel-
opment have been made during the past twenty years. Among those
sources accessible for this study are the reconnaissance geo-
logic mapping of Peterson and Mclntyre (1970) and the detailed
geologic studies by Hardyman, et al. (1972). The basic hydrol-
ogy of the region has been covered by Newcomb and Hart (1958),
Illian (1970) and Leonard and Harris (1974). The geothermal re-
source as a whole, including reconnaissance geophysics and geo-
chemistry, is covered by Sammel (1976). Many other geological,
geophysical and geochemical studies have been carried out on the
resource by private companies interested in geothermal explora-
tion, but most of this data was not available for use here.
4.1.3 Climatology
The Klamath and Cascade Mountains impede the easterly flow
of moist, temperate air from the Pacific Ocean into the Klamath
Basin region. The climate of this region is characterized by
warm, dry summers and cool to cold, more humid winters. Because
elevations vary from 1,200 m (4,000 ft) on valley floors to over
2,400 m (8,000 ft) in the mountains, there is a considerable
variation in local climatic conditions.
All weather stations in the Klamath Basin region are in the
lowlands. Klamath Falls and Klamath Falls airport (elevation
1,245m [4,085 ft]) are the most important data-gathering
points. Supplemental data from Fort Klamath and Chiloguin in
the north, from Keno in the west, and from Merrill and Malm in
the south part of the basin is also available.
213
-------
The chief source of data presented here is the Columbia
Basin Climatological Handbook, compiled by the Meteorological
Committee of the Pacific Northwest River Basins Commission
(1968-69). Unless otherwise noted, information given below is
from this source.
Temperature--
Maximum recorded temperatures range from 41°C (105°F) at
Klamath Falls (in 1911) to -32°C (-25°F) in Malin (in 1937).
The Klamath Basin has a short growing season. The first killing
frost (-2°C [28°F]) occurs on October 18, and the last on May 4,
on the average. However, temperatures of -2°C (28°F) or below
have been recorded each month of the year in Klamath Falls.
Figure 4.2 shows normal monthly temperature at Klamath Falls.
More detailed temperature data is given in Table 4.1. Mean
annual temperature at several stations for the period 1931 to
1960 is as follows: Chiloguin, 6.8°C (44.3°F); Klamath Falls,
9.1°C (48.3°F); Klamath Falls airport, 8.2°C (46.8°F). By
contrast the mean annual temperature at Crater Lake, at an
elevation of about 2,400 m (7,900 ft) in the Cascade Mountains,
is 3.8°C (38.9°F).
Precipitation—
Average annual precipitation in the region varies with
altitude. Lowland-station figures range from 477 mm (18.79 in)
at Keno and 450 mm (17.72 in) at Chiloguin to 357 mm (14.06
in) at Klamath Falls and 338 mm (13.34 in) at Klamath Falls
airport. Precipitation at Crater Lake, on the crest of the
Cascade Range, is 1,235 mm (48.61 in), and amounts of 1,525 mm
(60 in) or more are common along the crest. Figure 4.3 is a
histogram of annual precipitation for the period 1931 to 1972 at
Klamath Falls and Chiloguin.
Average monthly precipitation is shown in Figure 4.2 and
Table 4.1. Greatest amounts fall in December and January, and
least fall in the summer. In all, 70% of annual precipitation
falls between October and March. This precipitation generally
occurs as mixed rain and snow in the lowlands and as snow in the
mountains.
Wind—
Wind data is available only for Klamath Falls airport.
Average wind speed is about 10 km/hr (6 mph), varying from a low
of 7.1 km/hr (4.4 mph) in September to a maximum of 11.8 km/hr
(7.3 mph) in March. Peak wind speeds range from 32 to 40 km/hr
(20 to 25 mph) in summer to 72.5 km/hr (45 mph) in January.
Calm periods are least frequent during March through June
(averaging about 17%) and most frequent in October (33%).
Predominant wind directions have a trimodal distribution in all
months but May through August, when they are bimodal. The three
chief directions are south-southeast, west, and north to north-
northwest, and together they account for some 40% of all winds.
214
-------
V)
Ul
X
i,
o
Ul
PRECIPITATION
TEMPERATURE
-
-
—
•
—
—
__
—
-
—
-
-
-
/u
LU
60 2
LL)
cc
50 £
Ul
111
LU
c
o
40 ^
z
ui*
30 cc
i
3 8
TEMPERA!
JFMAMJJASOND
JF MAMJ JASOND
Figure 4.2 Normal monthly temperature and precipitation at
Klamath Falls.
215
-------
TABLE 4.1 MEAN MONTHLY AND ANNUAL TEMPERATURES AND PRECIPITATION, AND MEAN
EXTREMES OF TEMPERATURE, KLAMATH BASIN, 1931-60
Means
Jul
Aug. Sept. Oct. Nov. Dec.
Klamath Falls Airport
Jan. Feb. Mar.
T 28.8 33.8 37.1 M».7 51.1
P 1.62 1.06 0.85 0.61 1.19 0.98 0.12 0.21 0.53 0.99 1-37 1.81
Apr. May June
57.4 67.2 64.5 59.5 4y.2 33.2 31.6
Ann.
46.8
11.34
Chi1oqu i n
T 27.3 31.2 36.4 k2.3 Mj. *» 55-2 62.3 60.6 5*».6 Mj.6 35.7 30.6 M».3
?..7q 1.99 1.62 1.03 l.'to 1.09 0.32 0.28 0.65 l.M 2.75 2.76 J7-72
NJ
Klamath Falls Airport
January
July
Chiloquin
January
July
Mean Extremes of Temperature
Mean Minimum
20.4
50.6
14.7
37.4
Mean Maximum
37.2
83.9
38.8
84.3
-------
ro
<7U
20
M
UJ
X
o
z
Z 10
2
g
h-
H-
51 0
a °
oc
CL 20
•
|
z
<
10
n
P
[
:
i
CHILOQUIN
1931-60 normal, 17.72 inches.
t—
f—
~
"" "
™"
-
"•
1 n
-
—
p
-t
*—
-
-i
-
"™ ^
P
_
KLAMATH FALLS
'
— j— p
_—
r"i
-
r
-i ,
-
931-60 norn
•^.
">~
nal, 14
-
06 inches,
1 \
p
-
-
".
•»
_
-
T-fl r
-
-
° R § I 8 ?
Ok <7> m o> O>
n_n
•n
•
•
o
r*
at
Figure 4.3 Annual precipitation at Chiloguin and Klamath
Falls, 1902-72. (Leonard and Harris, 1974)
-------
Other winds are rather evenly distributed among the remaining
twelve points of the compass. South-southeasterly winds predom-
inate during the winter, west winds in the spring, and northerly
winds during the summer and fall. This data is summarized in
Table 4.2.
The extent to which winds at Klamath Falls airport charac-
terize those throughout Klamath Basin is unknown. However, it
may be guessed that the percentage calm and average speeds are
representative of much of the basin.
Humidity—
Relative humidity is reported only from Klamath Falls
airport. This is maximum when temperatures are lowest, in the
early morning hours. Seasonally, the diurnal maxima do not vary
much, ranging from 74% to 83%. Minima occur in late afternoon
and show large seasonal change, from 26% in July to 74% in
December.
Dew point is an indicator of absolute humidity. At Klamath
Falls airport, it shows slight diurnal change (about -17°C
[2°F]). Seasonal variation is large, from about -7°C (20°F) in
January to 8°C (47°F) in July. Presumably, the increase is
related to local evapotranspiration from irrigated fields and
lake surfaces.
Evaporation in Klamath Basin is not precisely known.
Average annual pan evaporation (class A) is estimated at 1,400
mm (55 in), and lake evaporation at 1,020 mm (40 in). This
high rate of evaporation reflects the low relative humidity of
the region.
Ground Fpg--
During the months of November through February, ground fog
occurs rather frequently in southern Klamath Basin. At Klamath
Falls airport, fog is reported 9.3% of the time in November, de-
creasing rather steadily to 2.6% in June. It averages about
0.5% in summer months (July to September) and 3.4% in October.
The detailed distribution of such fogs about the basin is
unknown, but the data from Klamath Falls airport may be con-
sidered characteristic of Lower Klamath Lake Basin.
Significant quantities of water vapor are released from
evaporative cooling towers of major power plants. Therefore,
geothermal electric power development, should it occur, could
cause significant local increases in ground fog in Lower Klamath
Lake Basin, particularly during the months of November through
February, when natural fogs are most frequent. For this reason,
the siting of such facilities may need to be considered in
relation to land uses adversely affected by such fog.
218
-------
TABLE 4.2 PREVAILING WINDS AT KLAMATH FALLS AIRPORT- PERCENTAL
FREQUENCY OF OCCURRENCE OF CALMS AND MODAL
WITH AVERAGE SPEEDS
Month
Calm
Directions
Average
Speed (mph)
January
February
March
April
May
June
July
August
September
20.8
20.6
16.7
18.6
16.6
17.5
25.0
27.3
27.9
SSE
W
N
SSE
N
W
W
SSE
NNW
N
W
NNW
SSE
N
W
NNW
N
W
NNW
N
NNW
W
N
NNW
W
N
NNW
N
W
15.5
8.9
7.7
13.2
10.9
9.7
14.8
12.0
8.3
7.4
14.5
11.6
8.2
7.7
18.8
13.9
9.6
18.0
16.1
9.8
18.0
13.4
10.8
15.0
11.9
7.2
15.8
12.6
8.7
11.2
8.0
6.6
10.7
5.5
8.4
9.6
11.5
7.3
6.5
8.7
8.7
11.4
5.9
7.9
9.1
6.4
7.5
8.7
6.9
8.3
6.9
6.1
8.1
6.2
5.4
7.1
5.3
6.9
219
-------
TABLE 4.2 (continued)
Month
Calm
%
Model
Dir.
Directions
Average
Speed (mph)
October
November
33.2
26.2
December
29.2
N
NNW
W
SSE
N
NNW
W
SSE
W
N
NNW
11.3
9.8
8.4
14.
10.
9.2
7.3
.5
,3
12.9
8.8
6.8
6.7
5.4
6.8
7.4
11.3
4.3
5.4
7.8
10.
8.
3.7
5.2
,7
,7
220
-------
4.2 GEOTHERMAL CHARACTERISTICS
Thermal springs and wells occur in areas of upwellinq
ground water. Circulation to 3,100 m (10,000 ft) is believed
likely. Warming of circulating ground water to more than 120°C
(250°F) may occur at those depths without a magmatic component
of heat. Data available at this time indicates that the most
intense zones of upwelling are along faults forming the east
side of the main graben trend. However, this conclusion must be
tempered by the observations that almost no drilling has been
done in the lake- and marsh-covered central graben area.
4.2.1 History of Geothermal Exploration and Development
There are several thermal springs in the Klamath Basin.
These include the now defunct hot springs at Klamath Falls, the
hot springs in Lost River at Olene Gap (sec. 14, T. 39 S.,
R. 10 E.) and the hot spring on the west shore of Upper Klamath
Lake at Eagle Point (sec. 23, T. 36 S., R. 7-1/2 E.). Addi-
tional thermal anomalies have been discovered in the course of
water well drilling. The most notable areas are in the eastern
part of the town of Klamath Falls, along the southwest side of
the Klamath Hills and at the north end of Stukel Mountain.
Klamath Falls—
Hot ground water at Klamath Falls has been utilized for the
space heating of homes, schools, and public buildings for more
than 70 years. The thermal water there is found in fractured
basalts and silicified lacustrine sediments (probably the Sedi-
mentary and Lower Basalt Aquifer units described in Section
4.4.2, below), along one or more faults in the graben complex.
The water is produced from depths ranging from less than 30 m
(100 ft) to a maximum of 550 m (1,800 ft) in a zone as much as 3
km (2 mi) wide northeast-southwest and extending for at least 8
km (5 mi) northwest-southeast. Temperatures in this zone range
from about 60°C (140°F) to 113°C (235°F). No holes have been
drilled beyond 550 m (1,800 ft). The deepest holes are on the
campus of OIT, at the north end of Klamath Falls. Development
of this zone is continuing and progressing southward. A KGRA
has been established here.
The average power derived from this resource is estimated
to be only about 5.6 MW and is used principally for space
heating some 500 structures in the city. These include homes,
businesses and public buildings (Lund, et al., 1974). Hot well
water has been used directly in heating and drinking water
systems in older installations. The water is then discharged to
the sewers and ultimately into the Klamath River. However,
present practice is to use downhole heat exchangers, with muni-
cipal water as the circulating fluid, minimizing the discharge
of either the slightly mineralized water or the spent warm water
221
-------
into the surface drainage. It is believed that only a small
part of total available hot water is currently used, and that
use will be expanded as conventional energy sources become more
expensive and less reliable.
Well water analyses indicate a TDS concentration of around
800 mg/1. Sodium and sulfate concentrations are highest, and
calcium and potassium concentrations are very low. Silica
concentration is typically about 70 to 90 mg/1 (Lund, et al.,
1974).
A few wells in the center of the hot water zone produce
small volumes of steam at low pressure. No deep drilling has
been done to determine whether a high temperature steam reser-
voir exists beneath the shallow hot water zone. This possibil-
ity is discussed below.
Olene Gap-Nuss Lake-Stukel Mountain Zone—
This rather poorly defined warm to hot water anomaly has
been explored on a small scale in only two areas. In Olene Gap,
a single residence near the hot spring is heated by a shallow
well. Further south, near Nuss Lake, seven temperature gradi-
ent holes were drilled to depths of about 80 m (260 ft). Except
for this, the zone has been outlined on the basis of water wells
drilled for irrigation and stock watering. The potential of the
area is unknown at present.
Klamath_Hills Zone—
This narrow zone of hot water wells extends along the
southwest side of the Klamath Hills for a distance of at least
5 km (3 mi). The anomaly is based on several irrigation wells
which produce water at rates between 1,500 and 3,800 1pm (400
and 1,000 gpm), at a temperature of about 85°C (185°F), from
depths of from 87 to 127 m (285 to 418 ft) (Peterson and Mcln-
tyre, 1970). After cooling, this water is used for irrigation.
Recently, several additional development wells with similar
yields and temperatures have been drilled in order to develop a
hot water resource for use in greenhouses or industry.
The only significant deep geothermal test well in the
Klamath Basin is located in the Klamath Hills. This was the
test drilled by Thermal Power Company near the center of the
south line of sec. 35, T. 40 S., T. 9 E., on the Klamath Hills
thermal anomaly (Plate 4.1). The well was drilled to a total
depth of about 1,800 m (5,900 ft), during the period June 12 to
July 29, 1976. It was abandoned for mechanical reasons, with
drill rods and other equipment jammed at about 670 m (2,200 ft).
The hole was lost before logging. A mud temperature of 103°C
(218°F) was found at a depth of about 140 m (459 ft), but the
temperature declined below this depth, becoming isothermal. It
was about 60°C (140°F) at 1,800 m (5,900 ft). This site was
selected after a series of shallow temperature gradient holes
222
-------
had been drilled. This data is not yet available. Ground noise
and electrical resistivity surveys had been carried out pre-
viously by Gulf Oil Company, from whom Thermal Power acquired
the greater part of its lease position.
The deep hole appears to have been drilled within the
complexly faulted Klamath Hills horst, northeast of the topo-
graphic and Bouguer gravity gradient which indicates a major
fault zone. The reversal of temperature gradient below 140 m
(450 ft) suggests that an unmapped fault was crossed near this
point and that the lower part of the hole was drilled in a
different and older block than was the upper part.
Results of this drilling discourage further prospecting in
the Klamath Hills horst itself, but it is possible that the
source of the greater than 93°C (200°F) water is at depth to the
west, toward the central basin. Temperatures at depth are
likely to reach or even exceed 150°C (300°F).
Other exploration companies hold leases in the Klamath
Basin and have conducted exploration programs here, but there
are no known plans for further deep testing of the basin at this
time.
4.2.2 Temperature Gradients
Several water wells provide temperature gradient data. From
these it can be seen that regional gradients are about 36°C/km
(2°F/100 ft). This is roughly average for crystalline rock in
the western United States. Gradient varies with heat flow and
thermal conductivity of rock, according to the relation
dQ = K dT
dT d~zT
Thus, for given heat flow, temperature gradient is higher in
poorly consolidated sediment (low conductivity) and lower in
crystalline rock (higher conductivity). For example, gradients
of 36° to 53°C per km (3° to 4°F per 100 ft) may be encountered in
unconsolidated sediments, under average western U.S. heat flow
conditions of about 1.5 to 2 heat flow units (HFU). Gradients
are altered by convective circulation of water along faults or
communication between aquifer systems.
Recharge along range fronts commonly is associated with
depressed gradients, with near-isothermal conditions olten
extending downward for several tens of meters. Upwelling
thermal water often is characterized by very high gradients
(occasionally to 80° to 180°C per km [5.5° to 11°F per ft]) in
shallow zones, and especially in alluvium.
223
-------
Several companies and government agencies have drilled
shallow temperature gradient holes in the Klamath Basin: Gulf
Oil Company, Natomas Company, Hunt Oil Company, Thermal Power
Company, Weyerhaeuser Company and the USGS, among others.
Proprietary information from the private companies is not avail-
able, but the USGS results were published recently (Sass and
Sammel, 1976; Sammel, 1976).
Two 180 m (590 ft) holes were drilled and logged by the
USGS during 1973 in the Lower Klamath Lake area, and temperature
gradients in many existing water wells were accurately logged.
It was concluded that local stratigraphic and hydrologic condi-
tions determine the temperature regime in most places (Sass and
Sammel, 1976; Sammel, 1976). Interfaces between basin sediments
and basalt flows, as well as lateral convective flow in perme-
able zones within the basalt sequences, influence temperature
gradients. Sammel (1976) concluded that observed heat fluxes in
shallow wells, some lower than 0.5 HFU, do not accurately relate
to temperatures at depth. Downward movement of cold water is
considered to cause such perturbation. Sass and Sammel (1976)
think that low thermal conductivity in fine-grained sediments
produces unrepresentative, high temperature gradients in many
basins.
4.2.3 Geothermal Potential
Geochemical data and temperature gradients indicate a
moderate temperature hot water reservoir, circulation and heat-
ing of meteoric water along major faults and mildly saline
water at depth.
Another possibility, although less likely, is that these
same factors indicate a high temperature vapor-dominated reser-
voir, whose fluids are diluted and cooled by mixing with meteo-
ric ground water as they rise toward the surface. Hydrochemical
data from formations underlying Pliocene basalts (described in
Section 4.3, below) is not available to help answer this ques-
tion. Only deep drilling can determine deeper conditions of
temperature and water quality. Appreciable amounts of hot water
may exist in the deep central Klamath Basin, perhaps at 3,000 to
4,000 m (10,000 to 13,000 ft). It is likely that abundant
thermal water occurs at drillable depths, principally in fault
zones, where isotherms are bowed upward. The availability of
this water in extensive areas in the eastern part of the Lower
Klamath Lake sub-basin suggests that continued development for
domestic and commercial space heating will take place. However,
the total thermal fluid in storage along these fault zones may
be trivial in comparison with commercial needs for electric
power generation. It is unknown whether deeper, as yet un-
sampled thermal fluids exist in quantities sufficient for com-
mercial power production.
224
-------
4.3 GEOLOGY
The physiography, regional geologic setting, tectonic
history and structure of the Klamath Basin region are discussed
in this section. The lithology, stratigraphy and more important
structural features of the two prominent geothermal areas in the
Upper and Lower Klamath Lake sub-basins are emphasized.
4.3.1 Physiography
The Klamath Basin is essentially coincident with the drain-
age basins of the Lost River and Klamath River, with its tribu-
taries, Sycan River, Williamson River and Sprague River. The
basin extends for a distance of about 110 km (70 mi) east from
the crest of the Cascade Range to the Quartz Mountain-Gearhart
Mountain area. The northern boundary of the basin is the low
drainage divide located near Chemult. From here it extends for
a distance of about 185 km (115 mi), to the edge of the Modoc
Lava Beds, California.
Throughout this region, major trends in the Cascade Range
are northerly. In general, valleys and ridges on the east side
of the basin trend northerly; but immediately north of the
Oregon border, they trend northwesterly. The structural sig-
nificance of this trend change is discussed in Section 4.3.3,
below.
Klamath Basin is a region of diverse topography. Its most
typical features are the large, flat-bottomed lake- or marsh-
covered depressions such as Klamath Marsh, Upper Klamath and
Agency Lakes, Lower Klamath Lake, Swan Lake and Tule Lake.
These sub-basins were covered by more extensive lakes during
Pleistocene time. The south part of Lower Klamath Lake, Swan
Lake and Tule Lake are basins of interior drainage, as are other
smaller sub-basins. Generally, lake bottom flatlands have a
surface relief of less than 30 m (100 ft), except where fault
blocks or eruptive centers protrude through them. The elevation
of the water surface in Upper Klamath Lake is approximately
1,260 m (4,140 ft). As the lake has a maximum depth of only
about 11 m (35 ft), the lake bed is about 1,250 m (4,100 ft) in
elevation. Elevations in the Tule Lake and Lower Klamath Lake
flatlands range from about 1,220 to 1,250 m (4,000 to 4,100 ft).
The main basins of the region are separated by upland areas
consisting of narrow, elongate, fault-block ridges, small,
lava-capped plateaus and volcanic piles.
The most important of the fault-block ridges are Bryant
Mountain (1915 m [6,280 ft]), Swan Lake Rim (2,210 m
[7,260 ft]), Stuckel Mountain (1,990 m [6,525 ft]), and Naylox
Mountain-Hogback Mountain (1,740 m [5,700 ft]). They have steep
flanking slopes; relief between ridgetops and adjacent flatianas
225
-------
often exceeds 180 m/km (1,000 ft/mi). These ridges are geologi-
cally youthful and are only very slightly dissected by stream
erosion. In some, such as Stuckel Mountain and Bryant Mountain,
faulting is so recent that undrained, sag-pond depressions are
still preserved. Uplift of these fault-block ridges during
Pleistocene time was an important factor in development of
impeded drainage and maintenance of extensive lakes. Only major
rivers have managed to cut through these uplifted ridges since
their formation, such as the Lost River at Olene Gap and the
Klamath River as it leaves the basin in the west.
Volcanic landforms are also important parts of upland
topography in the basin. On the west, apart from minor fault-
block ridges, volcanic landforms dominate the Cascade Mountains.
These comprise an upland plateau-like area, ranging from 1,200
to 1,500 m (4,000 to 5,000 ft) in elevation, made up of basalt
flows on which numerous shield and stratovolcanoes have been
built. Within the study area and vicinity, the largest eruptive
centers are as follows: Pelican Butte (2,449 m [8,036 ft]), the
Aspen Butte-Mount Harrison complex (2,502 m [8,208 ft]), Brown
Mountain (2228 m [7,311 ft]), Mount McLaughlin (2,894 m [9,495
ft]), Mount Mazama-Crater Lake (present rim elevation 2,438 to
2,469 m [8,000 to 8,100 ft]) and the Medicine Lake Highland
(2,134 to 2,225 m [7,000 to 7,300 ft]). Relief on the flanks of
the major volcanoes is steep, ranging from a few meters to over
180 m/km (1,000 ft/mi). Many smaller lava and cinder cones are
also present.
The various volcanic features present in this terrain
include the large caldera at Crater Lake and a smaller caldera,
now almost filled with resurgent lavas, at Medicine Lake.
Several of the Cascade Range eruptive areas are so young that
unvegetated aa and pahoehoe flow surfaces are still present, as
at Brown Mountain, Modoc Lava Beds and Medicine Lake Highland.
East of the Cascade Range, low basalt-capped plateaus are
present in several areas, notably north of Agency Lake and along
the north side of the Sprague River Valley. Isolated large and
small eruptive centers also occur in this region. The largest
is Yamsay Mountain (2,498 m [8,196 ft]), and smaller ones occur
closer to the geothermal area, such as at Hamaker Mountain
(2,010 m [6,596 ft]), Moyina Hill (1,736 m [5,696 ft]), Hopper
Hill (1,567 m [5,141 ft]) and Edgewood Mountain-Swan Lake Point
(2,040 to 2,213 m [6,694 to 7,260 ft]).
The volcanic features of the Klamath Basin region were
formed over a long period of time. Thus, the degree of ero-
sional modification they have undergone varies greatly. The
higher, older peaks, such as Yamsay Mountain, Pelican Butte and
Mount Mazama-Crater Lake, were eroded by glaciers during the
Pleistocene ice ages, and subsequently by streams. Other areas,
such as the Modoc Lava Beds and Brown Mountain, are essentially
unmodified by erosion.
226
-------
The geothermal prospect areas of particular interest in
this study are associated with buried fault zones parallel to
the steep flanks of linear ridge-blocks in the Upper and Lower
Klamath Lake sub-basins (Plate 4,1). The Klamath Hills Zone,
Klamath Falls City Zone and the broad zone extending from Olene
Gap around the northwest end of Stukel Mountain are all exam-
ples. Some geothermal anomalies also occur in areas of rela-
tively low relief, such as around Miller Hill and near Midland.
These are also believed to be associated with faulting, though
of smaller displacement than the others. Outside of the study
area, a few areas of warm water are reported in Poe, Yonna,
Langell and Sprague River Valleys, outlined by wells located in
the lowlands.
Mass-wasting processes such as landsliding or mud flow
activity are not significant in geothermal prospect areas in
particular, nor in the Klamath Basin as a whole. In addition,
many years of water withdrawal from the aquifers of the region
have not been reported to have caused ground subsidence. Ex-
traction of geothermal fluids over a period of several decades
in the Klamath Falls City geothermal field does not appear to
have affected land surface stability.
4.3.2 Regional Geologic Setting and Tectonic History
Rocks exposed in the project area are of late Cenozoic
volcanic and nonmarine sedimentary origin. In order to under-
stand the nature of underlying rocks and the older history of
the area, one must examine outcrops of older rocks located some
distance beyond the margins of Klamath Basin.
The oldest rocks in the region are exposed in the Klamath
Mountain, 56 to 80 km (35 to 50 mi) west of the basin. They
consist of slate, phyllite, greywacke, metavolcanic rock
(greenstone), and minor amounts of chert and marble, all
assigned to the Applegate Group, of probable Triassic age.
These rocks were strongly deformed and injected by serpentinite
bodies along major zones of faulting in late Mesozoic time.
During middle to late Cretaceous time, stocks of granitic to
dioritic composition, such as that exposed at Mount Ashland,
were intruded into this assemblage.
East and north of Klamath Basin, the pre-Cenozoic section
is buried beneath younger rocks over a distance of several
hundred kilometers, as far as the Blue Mountain of central
Oregon. However, based on the regional distribution of late
Paleozoic and Mesozoic eugeosynclinal metasediments and metavol-
canics, it seems probable that the Klamath Basin area is also
underlain by rocks of this type at some great but unknown depth.
Sedimentary rocks of late Cretaceous age overlie the older
igneous and metamorphic assemblage along a major unconformity.
These rocks, assigned to the Hornbrook Formation, dip eastward
227
-------
under the western Cascade Range between Medford, Oregon and
Yreka, California. They consist of conglomerate, greywacke
sandstone, siltstone and shale mostly of marine origin, ranging
over 900 m (3,000 ft) thick. Partly correlative marine sedi-
ments reappear in the Blue Mountains uplift in central Oregon,
to the northeast of the project area. However, a deep oil test
well drilled near Lakeview, the Humble Oil and Refining Company
Leavitt No. 1 (sec. 2, T. 40 S., R. 20 E.), is reported to have
penetrated volcanic rocks of Cretaceous age without finding
sediments equivalent to the Hornbrook Formation. Thus, the
subsurface distribution of these rocks under the Klamath Basin
is uncertain. If they are present and contain their original
connate marine water, they could influence the composition of
deeply circulating ground water.
A succession consisting of arkosic sandstone, conglomerate,
rhyolite to andesite ash-flow tuffs, tuffaceous sediments and
andesite and basalt flows overlies the Hornbrook Formation in
the southwestern Cascade Mountain. The term Western Cascades
Volcanic Series has been proposed for a partly equivalent assem-
blage farther north in the range, and the same term is loosely
applied here (Callaghan and Buddington, 1938). Along the west
side of the range and in the Klamath River Canyon, west of the
project area, these rocks dip eastward under the more recent
lavas of the so-called High Cascades Series. Several broad
stratigraphic units were outlined by Wells (1956) in the Western
Cascades section of the Medford quadrangle. These units were
poorly understood and their stratigraphy is currently under
revision. In Bear Creek Valley, the interval immediately above
the Hornbrook Formation, strata consist of a thick, lenticular
deposit of fluviatile tuffaceous, arkosic sandstone and cong-
lomerate containing a few coal seams. These rocks are infor-
mally referred to as the Payne Cliff Formation, which ranges in
thickness from about 60 to 1,800 m (200 to 6,000 ft) in a short
distance. The age of this formation is uncertain, but it di-
rectly underlies the Upper Eocene Colestin Formation, consisting
of andesite flows, mudflow breccia, tuff, conglomerate and
tuffaceous sediments. The Colestin Formation is highly lenticu-
lar in character, and its lateral relationship to the Payne
Cliff Formation is uncertain at this time. In view of the rapid
thickness and lithologic changes occurring in the section im-
mediately above the Hornbrook Formation, it is impossible to
resolve its configuration under the Klamath Basin.
The Little Butte Volcanic Group overlies both the Payne
Cliff and Colestin Formation. The thickness of this sequence in
its type area east of Medford is about 900 m (3,000 ft) (Wells,
1956). Here it is made up of two recognizable units. The lower
is predominantly andesite flows, flow breccias and agglomerates
assigned to the Roxy Formation. This unit is about 580 m
(1,900 ft) thick. The Wasson Formation, consisting of about
335 m (1,100 ft) of acidic ash-flow tuffs, flow breccias and
228
-------
local basalt flows forms the upper unit in the group. Recent
unpublished studies to the south indicate that the section
thickens dramatically in the vicinity of the Klamath River,
where undifferentiated thicknesses of Colestin Formation and
Little Butte Volcanics are reported to range from 3,700 m
(12,000 ft) to possibly 6,100 m (20,000 ft) (Williams, 1949;
Hammond, pers. comm.). Along the Klamath River, this thick
section contains a wide variety of lithologic units, including
andesite flows and breccias, basalt flows, thick acidic ash-flow
tuffs, tuffaceous sediments and minor diatomite. The radiomet-
ric age of the lower part of the Roxy Formation is about 30
million years, or Oligocene, according to unpublished data from
the USGS.
The uppermost formation of the Western Cascades sequence is
the Heppsie Andesite. This unit consists of thickly bedded
andesite flows of great but unknown thickness. Radiometric
dating indicates that it is of Miocene age. This section
appears to rest unconformably on the Little Butte Volcanics.
The Western Cascades sequence is separated from the over-
lying High Cascades Volcanics by an angular unconformity along
which a great deal of erosion occurred. As a result, these
younger volcanics may rest on a variety of older units, and the
section beneath them is unpredictable in any specific location.
Exposures of the Western Cascades sequence nearest the Klamath
Basin are in the canyon of the Klamath River, about 40 km
(25 mi) southwest of Klamath Falls. None of the fault-block
ridges within the basin are known to contain rocks as old as
this assemblage.
Sections of Oligocene and Miocene volcanic rocks are ex-
posed in fault-block ridges lying 80 or more km (50+ mi) east of
Klamath Falls (Peterson and Mclntyre, 1970). Reconnaissance
studies indicate that these rocks are partly equivalent in age
and similar in lithqlogy to the Western Cascades sequence.
Therefore, it is probable that the entire Klamath Basin is
underlain by these Miocene and older volcanics.
The nature of the Western Cascades volcanic rocks beneath
the Klamath Basin is known only in a general way, and the depth
at which they might be reached in deep geothermal exploration
wells is unknown. However, they may be present, at least in
local areas in and adjacent to horst blocks, at depths which
could make them the desired reservoir rocks in geothermal
prospects.
Only one well within the Klamath Basin has been drilled to
a depth which is likely to have penetrated these rocks. This is
the Thermal Power Company well in the Klamath Hills (SW 1/4,
sec. 35, T. 40 S., R. 9 E.)i drilled to a depth of 1,781 m
(5,842 ft). Data from this well is not available at this time.
229
-------
Following a period of tilting and erosion in late Miocene
or early Pliocene time, eruption of the High Cascades Volcanic
Assemblage began, accompanied by volcanism, faulting and lake
formation in Klamath Basin. The High Cascades Assemblage has
two main subdivisions. One of these contains extensive basalt
flows. These form a plateau-like region which is particularly
well exposed along both sides of the Klamath River Canyon south-
west of the Klamath Basin. Some low, relatively small eruptive
centers surrounded by similar basalts may be sources for these
flows. The second main group of High Cascades rocks consists of
lavas and pyroclastics which form the major shield volcanoes and
stratovolcanoes that characterize the range. These rocks are
typically andesites, but basalt and minor amounts of dacite are
sometimes present. Medicine Lake Highland, Mount McLaughlin,
the Aspen Butte-Mount Harriman complex, Pelican Butte and Mount
Mazama-Crater Lake are examples of this assemblage.
Paleomagnetic dating of some High Cascade volcanoes to the
north of the project area indicates that they were all built
during the last 1.5 million years. If, as is likely, the simi-
lar volcanic rocks of Klamath Basin are contemporaneous, then
widespread Quaternary magmatic activity is indicated. There-
fore, still-cooling intrusions are probably the source of the
geothermal anomaly in Klamath Basin.
There is no clearly defined boundary between the geologic
conditions of the High Cascades and those of Klamath Basin.
Rather, the entire basin is a zone of transition between the
Cascade Range and the Basin and Range Province. The eruptive
history of the basin contains many features like those of the
High Cascades, although no radiometric or other dating is avail-
able to determine exact time relations. Basalt-capped table-
lands are extensive in the basin, between the west flank of
Winter Rim and Chiloquin and in other areas. Also present are
small basalt eruptive centers, as well as a few large andesite
stratovolcanoes. The largest of these is Yamsay Mountain, in
the northeast part of the Klamath River drainage. Normal fault-
ing, which characterizes the Klamath Basin, extends into the
High Cascades and seems to be in some way related to the loca-
tion of eruptive centers there.
While volcanism continued, a period of lacustrine deposi-
tion occurred in Klamath Basin as a result of the impedance of
drainage by volcanic activity and faulting. x In late Pliocene or
early Pleistocene time, intensification of faulting created
present topographic and hydrologic conditions.
4.3.3 Structure
Only the broadest aspects of pre-Pliocene structural evo-
lution can be deduced from the available data. From Eocene or
Oligocene to Pliocene time, the region now occupied by the south-
230
-------
ern Cascade Mountains, the Klamath Basin and a large area to the
east was downwarped strongly and was the site of deposition of
large quantities of volcanic rocks and volcaniclastic sediments.
At present, these older Tertiary rocks dip east or northeast
along the western Cascade front in the Medford-Ashland-Yreka
area. Eighty or more kilometers (50+ mi) to the east of Klamath
Falls, they dip generally southwest toward Klamath Basin. In
the large area between these two outcrop belts, they are covered
by younger materials, so that their structure is unknown. A
major angular unconformity separates the older Tertiary volcanic
rocks from the Pliocene and younger lavas of the High Cascades.
During later Pliocene and Quaternary time, a system of
normal faults was superimposed on the regional downwarp. Evi-
dence of oldest faulting in this period consists of alignments
of small eruptive centers. Trends of these centers range from
northwesterly in the southern to northerly in the central
Klamath Basin, parallel to trends of later faults in the same
areas (Peterson and Mclntyre, 1970). Faulting reached a climax
in Pleistocene time. Since the latest major movements, the
Klamath and Lost Rivers have been able to establish exterior
drainage across the faulted topography, but numerous areas of
internal drainage remain.
Normal faulting in the Klamath Basin region occurs in a
zone about 50 to 65 km (30 to 40 mi) wide, from Buck Mountain,
Surveyor Mountain and Lake of the Woods, in the High Cascades on
the west, to near Bly Mountain, the Sprague River Valley and
Goodlow Rim on the east. Various segments of the trend extend
from the Tule Lake area of northern California, through southern
Oregon, to the Upper Klamath Lake Basin. Related structural
features are present even farther northeast, near Chemult
(Peterson and Mclntyre, 1970). This broad zone is flanked on
the west by relatively unfaulted rocks with an eastward to
northeastward homoclinal dip and by recent volcanic rocks which
are unfaulted. East of the fault zone, only a few minor faults
are present.
- Several generalizations can be made concerning normal
faulting within the study area (Plate 4.1):
1) Fault trends are consistent in strike. In the south-
ern two-thirds of the map area (Plate 4.1), the strike
is almost exclusively northwesterly. In the northern
third, fault strike becomes northerly. Gravity data
indicates that short, buried, northeast trending
faults segment the major northwest trending fault-
blocks.
2) Fault displacements diminish in magnitude both east-
ward and westward from the Klamath Lake area. Only a
231
-------
few faults, with negligible offset, occur west of the
Buck Mountain-Surveyor Mountain-Hayden Mountain trend.
A similar decrease is seen eastward from Swan Lake
Mountain. Within the Klamath Basin graben, displace-
ment varies from tens of meters to several hundred
meters.
3) Dips of fault planes range from about 55° to 60° at
the surface but might decrease with depth. Many of
the faults show "scissoring," wherein vertical dis-
placement decreases to zero along strike and then
increases but in a reversed sense.
4) The common sense of movement is stepwide downdropping
of blocks, going from the east and west sides of
Klamath Basin towards its axis. Within the graben
complex, large subsidiary horst and graben blocks have
developed.
The close relationship between geothermal anomalies and the
fault pattern may be seen by a comparison of the surface geo-
logic map (Plate 4.1) with temperatures of ground water (see
Section 4.4, below). It is apparent that fault zones provide
major conduits for the circulation of both cold and heated
ground water and that they localize the known geothermal
anomalies.
With one exception, geothermal anomalies within the study
area occur along the faults bounding the east side of the inner
part of the graben complex. The exception is the hot spring at
Eagle Point, just west of the graben center.
Geologic structure in the main geothermal areas is sum-
marized briefly below.
Klamath Falls Hot Water Field--
The best known geothermal anomaly in the region underlies
part of the city of Klamath Falls. The area of highest tem-
peratures occurs in a northwest trending zone parallel to nearby
faults. The fault along the southwest side of Bald Hill Ridge
appears to form the eastern boundary of this field (Plate 4.1).
Minor faults within the productive area isolate reservoirs to
some degree, as shown by differing depths of producing horizons
in different fault-blocks. They also provide the main channels
for upward circulation of hot water which then spreads laterally
in permeable zones.
The faults in this geothermal field are not the most sig-
nificant in the immediate vicinity, and reasons for the restric-
tion of upward hot water movement to this particular area are
not readily apparent.
232
-------
Olene Gap-Nuss Lake-Stukel Mountain Zone—
This is a large, poorly defined thermal area including the
hot spring at Olene Gap and warm water wells in the adjacent
area on the west and southwest around the edge of the Stukel
Mountain horst. The Olene Gap Hot Spring appears to be related
to the north and northwest trending faults which bound both
sides of the adjacent ridge to the north. These seem to con-
verge and possibly intersect in the gap. Surface geology does
not support the presence of a major north-northeast trending
fault passing through the gap, as proposed by Peterson and Groh
(1967). However, gravity data indicates that a northeasterly
trending fault is probably present at the northwest end of
Stukel Mountain, intersecting numerous north and northwest
trending faults, some of which bound the horst block. The Nuss
Lake warm water occurrences are located in this complex of fault
intersections.
Occurrences of warm water continue along the southwest side
of Stukel Mountain in the boundary fault zone.
Klamath Hills Hot Water Zone—
- A narrow, northwest trending zone of hot water wells runs
along the southwest side of the Klamath Hills horst, near the
major fault or fault zone that bounds it. The precise location
of this fault is unknown, but gravity data indicates a position
within 1.6 km (1 mi) of the southwest side of the hills, beneath
the valley alluvium. This appears to be one of the largest
faults of the region in terms of its gravity expression,
although it is not related to a topographically high horst
block, in comparison with most other known major faults of the
region. This may imply a greater age for this feature.
Other isolated minor thermal anomalies are present along
the Klamath Hills Fault trend near Midland, and in the newly
discovered Greensprings Drive subdivision, north of the Klamath
River and Highway 66. , A few warm water wells also occur in
small northwest trending fault zones, such as at Miller Hill.
Eagle Springs Zone—
The isolated Eagle Springs warm water area lies on the
shore of Upper Klamath Lake at Eagle Point (sec. 23, T. 36 S.,
R. 7 E.)- This spring is located along a prominent fault bound-
ing the ridge. The extent of the thermal anomaly is unknown.
As noted above, this occurrence is unusual because of its loca-
tion on the west side of the graben axis.
4.3.4 Stratigraphy and Lithology
Formal stratigraphic names have not been applied to most of
the rock units occurring here. In the following, these units
will be referred to by the symbols identifying them on the
accompanying geologic map (Plate 4.1). As currently known from
reconnaissance mapping, all rocks exposed in the study area are
233
-------
of middle or late Pliocene to Holocene age. Two broad strati-
graphic successions are present: one is found in fault-block
ridges along the east side of the central lowland; the other
occurs in hills along the west side of the basin and in the
adjacent High Cascades. Henceforth, they will be referred to as
the west- and east-side sections.
The lack of recognizable horizons common to both sections,
and of radiometric age-dates, precludes making any but the most
tentative correlations between them. The east-side section
contains prominent lacustrine rocks as well as basalt flows.
This lacustrine facies thins toward the large eruptive centers
of the High Cascades, where the section is made up almost
entirely of flows, breccias, and cinders of basaltic and ande-
sitic composition. In order to avoid confusion, the east- and
west-side sections are described separately.
East-Side Section—
(Tb) - Basalt, dark flows and flow breccias; (Tbp) - coarse
palagonitic tuffs; (Tbc) - basalt eruptive centers; (Tbcc) -
basalt cinder cones—All rock types in this group are believed
to be essentially contemporaneous with one another and to repre-
sent different phases of the same eruptive cycle. They are
exposed in horst-blocks along the west side of the Upper and
Lower Klamath Lake sub-basins, such as Naylox, Hogback, Stukel
and Bryant Mountain. The base of the section has not been
identified in any of these exposures (Fig. 4.4).
Two main facies comprise this lithologic group. One lies
entirely outside of the map area, from Chiloguin to within about
1.5 km (1 mi) of the north edge of the map (Plate 4.1), and is
made up of coarse palagonitic tuff containing basalt scoria and
flow breccia. This material often exhibits high initial dips,
suggesting that it was piled up around eruptive centers. Alter-
ation of the glassy basalt cinders and tuff to a brown palagon-
itic clay-zeolite mixture suggests that these materials formed
lake deposits. Passing southward into the map area, one finds a
different facies, composed of numerous 3 to, 6m (10 to 20 ft)
thick basalt flows and agglutinated flow breccias. These are
mainly dark grey and fine-grained, containing a few plagioclase
phenocrysts. A few thin basalt flows with diktytaxitic texture,
water-laid cinder lenses and piles of palagonitic tuff are
interbedded with the dominant flows.
Rapid local facies changes occur near the numerous small
volcanic vents. For example, a tuff mound surrounded and over-
lapped by flows can be seen along the Plum Hills scarp (E 1/2,
sec. 31, T. 37 S., R. 9 E.). To the south, at large quarries in
the west face of the Stuckel Mountain fault-block, one finds
coarse agglutinated basalt breccia, which is probably a near-
vent deposit. Because known faults are the loci of both most
rock exposures and ancient eruptive centers, it is believed that
lithologic variations seen in outcrop are not representative of
234
-------
ORIQIHAL
FAULT
SCARP—
r_.
UPPER KLAMATH
LAKE-^
NJ
(JO
Ul
•IMPERMEABLE LAYER
HEAT AND MOISTURE
MOVEMENT IN THE
FORM OF STEAM AND
HOT GASES
HEAT SOURCET
Figure 4.4 Diagrammatic section of east side of Klamath graben
-------
this rock group as a whole. That is, relatively homogeneous
flows probably occupy most areas between faults.
The exposed section is at least 450 m (1,500 ft) thick at
Naylox Mountain, more than 600 m (2,000 ft) thick at Stukel
Mountain and of even greater probable thickness in Bryant
Mountain.
This lithologic group has the greatest shallow reservoir
potential for geothermal fluids. Therefore, abrupt facies
changes and their effects on reservoir characteristics are
likely to be an important factor in geothermal development in
the region.
Water well data in the region indicates that the basalt
flow and flow breccia parts of the (Tb) interval are highly
porous and permeable; many high-yielding irrigation wells pro-
duce from it. Based on limited lithologic data contained in
well drillers' reports, it appears that water comes from frac-
tures in flows and from interflow rubble and cinder zones. Hot
water in geothermal zones of the area is also obtained from this
unit. The small amount of lithologic data available from geo-
thermal wells indicates that the basalt aquifer is not severely
altered by thermal fluids, even though the overlying diatomite
has been converted to porcellanite and opal breccia.
Relationships between the (Tb) unit and lacustrine rocks of
the (Tp) unit are complex. It is probable that the (Tb) erup-
tives impounded drainage, creating the lakes in which the pre-
dominantly sedimentary (Tp) unit was deposited. (Tp) sediments
locally overlie (Tb) on ridges along the east side of the basin.
However, it seems likely that the (Tb) phase was partly contem-
poraneous with the lacustrine (Tp) phase. Thus, the two units
probably interfinger in some places.
The age of the (Tb) unit is not known directly. Overlying
lacustrine sediments (Tp) have been dated as of middle or late
Pliocene age; the youngest Western Cascades volcanic rocks
believed to underlie the unit are of Miocene age. Thus, it is
likely that the (Tb) basalts are of early to middle Pliocene
age.
(Tp) - Diatomite and palagonite-tuff sandstone and silt-
stone; (Tpb) - basalt flows and shallow intrusives in the lacus-
trine sediments—This unit is widely exposed in the project area
and beyond. Major outcrop areas occur in small fault-blocks in
and around Klamath Falls; on the east slope of Hogback and
Naylox Mountain, where it overlies the (Tb) basalts; in the
Stukel Mountain block also overlying (Tb); in the Klamath Hills;
and in the floor of Yonna Valley to the east (Peterson and
Mclntyre, 1970). Based on gravity studies, it is presumed to
make up most of the thick low density section present in the
Lower Klamath Lake sub-basin (Peterson and Groh, 1967).
236
-------
The characteristic rock types in the unit are compact,
massive-bedded white diatomite and moderately well-indurated
grey-brown palagonitic tuff and tuffaceous sediments. These
sediments are of lacustrine origin.
Other rock types are important locally. Among them are
coarse palagonite tuff and basalt scoria and bombs, marking
eruptive centers. These centers form ringshaped mounds which
are particularly well exposed in Meadow Valley, along the west
side of Swan Valley and in the north end of Yonna Valley.
Basalt flows, sills and dikes are also locally present in
the lacustrine rocks. The basalt is dark grey to black, finely
crystalline to glassy, often with scattered phenocrysts of
olivine and plagioclase. Pillow structures sometimes seen in
the flows indicate that they cooled under water. Examples of
intrusive basalts can be seen in a quarry in NW 1/4 sec. 11, T.
39 S., R. 8 E. Flows interbedded within the section can be seen
in highway cuts near the center of sec. 5, T. 35 S., T. 9 E., and
in many other places. These basalts have been mapped as a
separate unit (Tpb) where exposures are large enough to be seen
on the scale of the map (Plate 4.1).
Thickness trends in the (Tp) unit are unknown. Partial
sections a few tens of meters thick are exposed in fault-block
uplifts around the edges of Upper and Lower Klamath Lake, and
good exposures can be seen to the east in Yonna and Poe Valleys.
Drillers' logs show thicknesses frequently exceeding 300 m
(1,000 ft).
Gravity data indicates that a section of low density mate-
rial as much as 1,800 m (6,000 ft) thick may occur under the
Lower Klamath Lake sub-basin, southwest of the Klamath Hills
Fault Zone (Peterson and Groh, 1967). Much of the low density
material causing the anomaly is likely to consist of (Tp)
sediments.
Lacustrine sediments (Tp) are present in all of the geo-
thermal areas discussed here. They have been hydrothermally
altered to hard, flinty opalite in the Klamath Falls geothermal
field and also, to a minor extent, in the Klamath Hills area.
Porosity and permeability in the (Tp) unit are generally low.
Thus, it may serve as a cap rock over more porous basalts in the
underlying (Tb) unit.
The assigned Pliocene age of the (Tp) unit is based on the
presence of diatoms (Pliocene) in the section near Dorris,
California, and on a few vertebrate fossils found near Stukel
Mountain (middle Pliocene) and Merrill (late Pliocene) (Peterson
and Mclntyre, 1970; Hanna and Gester, 1963).
237
-------
(Qtbf) Basalt flows—A tableland basalt sequence overlies
(Tp) lake beds in the northwest corner of Swan Lake Valley,
northeast of the geothermal areas. This unit consists of
several light grey flow units with diktytaxitic texture. it
reaches a maximum thickness of about 45 m (150 ft). These flows
form the surface of an eroded plateau which is analogous to, if
not correlative with, the similar plateau north of Sprague River
and Chiloquin. This basalt unit also may be related to the
plateau-forming basalts of the High Cascades Sequence, but no
precise correlation has been established.
The (Qtbf) unit is younger than the upper Pliocene (Tp)
lake beds on which it rests. It has been subjected to both
faulting and considerable erosion and is thus probably of late
Pliocene or early Pleistocene age. As yet, it has not been
recognized in the downfaulted sections penetrated by water wells
in the Lower Klamath Lake sub-basin.
(Qal) - Silt, sand, gravel, diatomite, peat and pumice—In
many parts of the area, (Tp) is the youngest unit present.
However, after the period of intense normal faulting had estab-
lished the present topographic framework, sedimentation con-
tinued in the lowland areas. A variety of sediments is present
in these young basins: coarse scree slopes and fans along the
steep range-fronts; river-deposited silts and sands; clay and
diatomite in the lakes; and extensive reed-sedge peat in
marshes. Locally, thin pumice deposits are present, perhaps
derived from sources to the southwest.
All of these materials have been mapped as undifferentiated
Quaternary alluvium. Only a few feet of this section is exposed
in any single location. Descriptions on water well logs are
usually not sufficiently detailed to distinguish between sedi-
ments of the present lacustrine cycle and those of Pliocene age.
Thus, the thickness of this material is not yet known. It is
estimated to reach a maximum of only a few tens of meters in the
central part of the present basin.
In general, these Quaternary deposits are poorly consoli-
dated. As the bulk of the section is fine-grained, it does not
contain important aquifers. Where the unit is thick enough to
be of any significance to geothermal development, it probably
comprises part of the overall cap rock interval, and it is not
anticipated that any geothermal development would withdraw
fluids from it.
West-Side Section—
The stratigraphic succession in this area can be tenta-
tively divided into four major assemblages. Each of these has
been subdivided into local volcanostratigraphic units during
field mapping. However, only a summary of the larger intervals
has any significance in the present study.
238
-------
Unit 1—The oldest rock assemblage appears to consist of
the basalt flows and small eruptive centers of Spence Mountain
and Eagle Point Ridge, (QtbSpc), the basalt flows of Indian
Springs Ridge (QtbISP and QtblSPc), and the basalt flows of
Mount Harrison (QtbHC, QtbH). These rocks are dark grey,
finely-crystalline basalts containing a few percent of small
plagioclase phenocrysts. Near eruptive centers, large amounts
of agglutinate and cinders are present. These rocks are grouped
together on the basis of their similar macroscopic appearance,
although their field relationships are not known. Their appear-
ance also suggests that they are correlative with the (Tb)
basalt unit on the east side of Klamath Lake. Eruption of these
rocks predates the extensive normal faulting in the region.
Field evidence indicates that they underlie flows of the next
unit discussed below. The thickness of this assemblage is un-
known, as the base is not exposed. The Weyerhaeuser Spence
Mountain geothermal gradient hole, drilled on the flank of the
Spence Mountain Eruptive Center (NE 1/4 sec. 15, T. 37 S., R.
7 E.), penetrated 611 m (2,006 ft) of rocks belonging to this
section, apparently without reaching its base.
Unit 2—This assemblage consists mainly of extensive thin
flows of light to medium grey, fine-grained holocrystalline
basalt (Qtbha and Qtbhad). The abundance of plagioclase in this
rock imparts both an unusually light color and a high alumina
content. Texturally, the rock ranges from aphanitic, to
slightly porphyritic and diktytaxitic. The diktytaxitic variety
forms the plateau surface of Johnson Prairie and other upland
areas bordering the Klamath River Canyon, where over 180 m
(600 ft) of these lavas rest unconformably on the western Cas-
cades Volcanics. It is present as the uppermost part of the
flow sequence on ridges between Aspen Lake and Howard Bay, where
it overlies the assemblage described above.
Basalt of a similar appearance (Qtbh) makes up several of
the moderate-sized volcanoes of the High Cascades, such as
Grizzly Mountain, Parker Mountain, Little Chinquapin Mountain
and others. These may have been the sources for some or all of
the extensive flows. The age and correlation of the (Qtbh)
rocks is not precisely known. As noted above, they overlie the
basalt assemblage believed to be correlative with (Tb) east of
Klamath Lake. They are themselves similar in appearance to the
flows of the (Qtbf) sequence east of the lake and are believed
to be essentially contemporaneous with them. These flows have
been faulted and deeply eroded by the Klamath River.
Unit 3—Following the eruption of the (Qtbh) suite and the
climax of faulting, several closed topographic depressions were
formed in the High Cascades. Diatomite, palogonite tuff, and
other volcaniclastic materials were deposited locally in lakes
that occupied these depressions. These have been mapped as
(QTtr, Qol and Qold). The most extensive of these deposits
239
-------
occur in the graben complex northwest of Keno. The age of these
rocks is not precisely known but they appear to be younger than
the very similar materials east of Klamath Lake (Tp) and to
overlie the (Qtbh) basalt flows.
Unit 4—A number of volcanic events occurred in the High
Cascades during and after the later stages of faulting. The
most notable one built the major stratovolcanoes of the range,
whose peaks are believed to be younger than the (Qtbh) flows and
are mostly unaffected by faulting. The highest peaks had
reached their present elevation before the most recent stage of
glaciation. However, eruptions at Brown Mountain, Crater Lake
and the Medicine Lake Highland have all occurred in post-glacial
time. As noted earlier, recent studies in the central Cascade
Mountains indicate that this eruptive cycle began about 1.5
million years ago.
A number of local volcanic units can be recognized around
specific eruptive centers, such as the basalt and andesite flows
(QbWFPc, QbWFP, QbAB, and related rocks), shallow intrusives
(Qbsip) and cinder cones (Qtbcc, Qbcc) shown on Plate 4.1.
These are of local interest only and are not discussed further
here.
4.4 HYDROLOGY
4-4-1 Surface Water
Topography and Drainage—
The Klamath physiographic basin, or greater Klamath drain-
age basin, includes the upper part of the Klamath River drainage
basin, as well as part of the Lost River Basin, and several
smaller closed basins, such as Swan Valley, Crater Lake, and
Lower Klamath Lake. This area comprises some 14,800 sq km
(5,700 sq mi). Of this, about 4,150 sq km (1,600 sq mi) contri-
butes little or no surface water to the Klamath River System,
except that which is artificially diverted to it from the Lost
River (Phillips, 1969).
The greater Klamath drainage basin is bounded on the west
by the crest of the Cascade Range, which separates it from the
Rogue River Basin. On the north, the divide between the Klamath
River Basin and that of the Deschutes-Columbia System occurs on
a low plateau north of Klamath Marsh. On the northeast and east
it is separated from the various interior drainage basins of the
Basin and Range Physiographic Province by a divide extending
southward from Winter Ridge to Barnes Rim.
In this area of youthful topography, as described by New-
comb and Hart (1958), the valley plains are imperfectly con-
nected by a rudely integrated drainage system which collects
240
-------
downstream in the Klamath River proper. The Williamson River,
the principal headwater stream, rises in a spring zone in the
SE 1/3 sec. 4, T. 33 S., R. 11 E. While flowing northward for
26 km (16 mi), it receives the flow of several springs and of
Deep and Jackson Creeks, which drain the west side of Yamsay
Mountain, and of Jack Creek, which drains the northeastern part
of the basin. It then turns westward and flows about 6 km
(4 mi) across a pumice plain to the northeastern end of the
Klamath Marsh. In Klamath Marsh it receives the flow of Big
Spring Creek and other smaller creeks. Two of these, Scott and
Band Creeks, drain from the east side of Mount Mazama-Crater
Lake. From Klamath Marsh the Williamson River flows over a
basalt rim near Kirk, descending about 90 m in 8 km (300 ft in 5
mi), and continues south where it discharges into Upper Klamath
Lake after receiving the Spring Creek and Sprague River inflows.
The north and south forks of the Sprague River rise on the
flanks of Gearhart Mountain, at the east side of the basin.
About 6 km (4 mi) northwest of Ely, they join to form the main
river. After flowing through Beatty Gap, the Sprague River is
joined by the Sycan River from the north. Several creeks and
springs enter the river as it flows an airline distance of 40 km
(25 mi) westward, through the lowland known as the Sprague River
Valley, to its confluence with the Williamson River near Chilo-
quin. Wood River and Sevenmile Creek separately drain southward
into Agency Lake, which is a northern lobe of Upper Klamath
Lake, now nearly separated by the encroachment of the delta of
the Williamson River.
Along the western side of Upper Klamath Lake, several
creeks, including Threemile, Cherry, Rock, Fourmile and Rocky
Creeks, enter from the Cascade slope.
The surface of Upper Klamath Lake stands near 1,260 m
(4,140 ft) in altitude, but varies seasonally by several feet
and is controlled, in part, for power generation and irrigation.
This is the largest natural lake wholly in Oregon, covering
approximately 40 sg km (15 sq mi). A low dam in the Link River
at the south end of the lake regulates the lake level, and
controls the release of about 54,300 ha-m (440,000 acre-ft) per
year, between the 1,261 and 1,263 meter (4,137 and 4,143 ft)
lake levels (Phillips, 1969).
Outflow from Upper Klamath Lake is through Link River, a
short, narrow, rockbound trench which descends about 12 m
(40 ft) to Lake Ewauna. Out of Lake Ewauna the main stem of the
Klamath River flows along the northwest side of the extensive
Klamath Valley lowland and the wide playa and marsh known as
Lower Klamath Lake. It then passes through basalt ridges near
Keno at an altitude of about 1,235 m (4,050 ft). The river
descends through a deep youthful canyon below Keno and enters
241
-------
the State of California at an altitude of about 900 m
(2,960 ft).
Lost River Basin is a separate river basin, but because use
of its water for irrigation is so much integrated with that of
the Klamath River, and because it partly occupies the same
structural basin, it is included here as part of the Klamath
Basin in Oregon. Headwaters of Lost River gather in the moun-
tains and plateaus forming the youthful topography athwart the
Oregon-California line east of Klamath Valley and Tule Lake
Basin. There are storage reservoirs on the tributaries, the
outflow of which is used mainly for irrigation. Through Olene
Gap, Lost River enters Klamath Valley at an altitude of about
1,250 m (4,100 ft) and flows southward into Tule Lake, a lake-
sump whose bed stands about 14 m (45 ft) below the floor of
Lower Klamath Lake, from which it is separated by narrow ridges.
Natural drainage in the Lost River and Lower Klamath Lake
areas has been considerably modified by irrigation and drainage
works. Much of the flow of Lost River is diverted into the
Klamath River drainage and other irrigation canals by a small
dam in the SW 1/4, sec. 29, T. 35 S., R. 10 E.; at certain
times, water from Klamath River is also diverted into Lost
River. Lower Klamath Lake, formerly an extensive marshland, has
been altered by construction of the Southern Pacific Railroad
and Highway 97 embankment along the northwest side of the basin.
Water is impounded on the west side of this embankment. To the
east, the floor of the old lake is now drained by a series of
canals and is under cultivation.
The KGRAs in the region treated herein are located in the
southern part of the Klamath Basin drainage system. The hot
spring at Eagle Point flows directly into Upper Klamath Lake.
The original thermal springs at Klamath Falls and the present
effluent water from hot water wells enter the system below Link
River. The Olene Gap Hot Springs enter Lost River, and any
effluent produced around the north and west ends of Stukel
Mountain would also reach this system. Geothermal effluents
from the development of the hot water zone along the south side
of the Klamath Hills would flow naturally into Lower Klamath
Lake. However, since that area is now drained by a series of
canals and the old lake bottom is under cultivation, the efflu-
ent would enter the canal system and drain southward into the
White Lake Sump, where it would evaporate.
Streamflow—
A summary of streamflow data in Klamath Basin is given in
Table 4.3. Principal uses for surface water in the Oregon part
of the drainage system are irrigation and industrial use by the
forest product industry. A further important use is the pres-
ervation of the habitat for migratory water fowl. Wildlife
refuges are established on Klamath Marsh, Upper Klamath Lake,
242
-------
TABLE 4.3
SUMMARY OF STREAM FLOW DATA AT SELECTED POINTS IN THE KLAMATH BASIN
(a) Summary of streamflow data at selected sites in the Klamath River Basin
Streamflow
Stream
Williamson River near Klamath Agency
Sprague River near Beatty
Sprague River near Chiloquin
Williamson River below Sprague River
Link River at Klamath Falls
Klamath River at Keno
Klamath River below John C. Boyle powerplant
Drainage
area
(square
miles)
1,290
513
1,580
3,000
3,810
3,920a
4,080a
Average
Years of
record
12
16
45
49
62
46
7
Cubic feet
per second
236
306
555
1,013
1,603
1,678
1,767
Acre-feet
per year
170,900
221,500
401,800
733,400
1,161,000
1,215,000
1,279,000
Cubic feet
per second
Maximun
1,590
6,980
14,900
16,100
9,400
9,250
8,830
Minimum
0
57
50
320
17
26
311
^
Excluding adjacent basins of Lost River and Lower Klamath Lake.
K)
4S*
U>
(b) Link River at Klamath Falls, Oregon
LOCATION: Lat 42°13'25", long 121°47'35", in SW 1/4 NW 1/4 sec. 32, T. 38 S., R. 9 E., Klamath County, on right bank
600 ft upstream from outlet of Keno Canal and 0.4 mile upstream from Main Street Bridge at Klamath Falls.
DRAINAGE AREA: 3,810 sq mi, approximately, Including 26.2 sq mi in closed basin of Crater Lake.
PERIOD OF RECORD: May 1904 to September 1970. „
GAGE: Water-stage recorder. Datum of gage is 4,083.71 ft above mean sea level; or 4,085.50 ft above mean sea level,
datum of Bureau of Reclamation. See WSP 1929 for history of changes prior to Nov. 16, 1961.
AVERAGE DISCHARGE: 66 years, 1,538 cfs (1,151,000 acre-ft per year), not adjusted for "A" Canal.
EXTREMES: Maximum and minimum discharges, in cubic feet per second, for the water years 1966-70 are contained
in the following table:
-------
TABLE 4.3 (continued)
Maximum
Minimum daily
Wtr yr
1966
1967
1968
1969
1970
Date
Nov. 5, 1965
May 13, 1967
Mar. 25, 1968
Apr. 5, 1969
Jan. 31, 1970
Discharge
4,250
5,320
3,360
6,980
7,270
Date
July 17, 1966
Mar. 17, 1967
Aug. 25, 1968
Dec. 15, 1968
May 7-9, 1970
Discharge
99
120
74
104
108
Period of record: Maximum discharge 8,400 cfs May 12, 1904 (gage height at Main Street Bridge, 7.30 ft,
datum then in use, from floodmarka); minimum daily, 17 cfs Dec. 13, 1937.
REMARKS: Records good. Flow regulated since 1919 by Upper Klamath Lake (see station 11507000). Large diurnal
fluctuation caused by powerplant above station. Water diverted above station by main or "A" Canal of
Klatnath project (see station 11506000). Many other diversions above lake. All records presented herein
include flow in Keno Canal which, since September 1908, has diverted from Upper Klamath Lake at Link
River Dam for power generation, and returns flow to Link River below station.
to
(c) Diversion from Klamath River to Lost River near Olene, Oregon
LOCATION: Lat 42"08'25", long 121°41'20", in NE 1/4 NW 1/4 sec. 31, R. 39 S., R. 10 E., Klamath County, on south
bank of Lost River diversion canal, 9.5 mile east of bridge on State Highway 39, 019 mile downstream from
dam on Lost River, and 3.8 miles southwest of Olene.
PERIOD OF RECORD: April 1931 to September 1968 (discontinued). Published with records for Lost River diversion
canal near Olene In 1931.
GAGE: Nonrecording gage. Altitude of gage is 4,080 ft (from topographic map).
AVERAGE DISCHAGE: 38 years, 35.1 cfs (25,430 acre-ft per year).
EXTREMES: Maximum and minimum discharges, in cubic feet per second, for the water years 1966-68 are contained
in the following table:
Maximum daily
Minimum
Wtr yr
1966
1967
1968
Date
Apr. 2, 1966
June 16, 1967
June 21, 1968
Discharge
705
587
714
Date
At times
do.
do.
Discharge
0
0
0
Period of record: Maximum daily discharge, 710 cfs Apr. 15, 1951; no flow at times.
-------
TABLE 4.3 (continued)
REMARKS: Records fair. Discharge computed from daily record of gate openings and gage readings at wasteway with
coefficients applied based on discharge measurements. Canal was built to divert water from Lost River to
Klamath River and thereby aid in reclamation of Tule Lake (see station 11486000). Beginning in April
1931, water has been diverted at times from Klamath River and released into Los River, from which it is
rediverted for irrigation of lands near Tule Lake. Since 1949, records include water removed from the
diversion canal by Miller Hill pumping plant (capacity, 105 cfs).
(d) Klamath River at Keno, Oregon
LOCATION: Lat 42°08'00", long 121°57'40", in NW 1/4 SE 1/4 sec. 35, T. 39 S., R. 7 E., Klamath County, on left
bank 1.7 miles northwest of Keno and 4.5 miles upstream from Spencer Creek.
*
DRAINAGE AREA: 3,920 sq mi, approximately (not including Lost River or Lower Klamath Lake basins).
PERIOD OF RECORD: June 1904 to December 1913, October 1929 to September 1970. Monthly discharge only October
to December 1929, published in WSP 1315-B.
GAGE: Water-stage recorder. Datum of gage is 3,961 ft above mean sea level (from river-profile survey). See
ji. WSP 1929 for history of changes prior to June 10, 1964.
01
AVERAGE DISCHARGE: 50 years, 1,665 cfs (1,206,000 acre-ft per year).
EXTREMES: Maximums and minimums (discharge in cubic feet per second, gage height in feet) for the water years
1966-70 are contained in the following table:
Maximum Minimum
Date Discharge G.H. Date <, Discharge
Nov. 5, 1965 4,270 9.03 July 18, 1966 239
May 14, 1967 6,070 10.34 July 20, 1967 . 188
Dec. 19, 1967 2,900 7.82 June 1-2, July 22,23, 1968 248
Apr. 4, .1969 7,880 ^ 11.47 July 13, 1969 207
Jan. 29, 1970 8,920 12.08 June 30, July 1,2,4, 1970 234
Period of record: Maximum discharge, 8,920 cfs Jan. 29, 1970 (gage height, 12.08 ft); minimum, 26 cfs
Sept. 23, 1956; minimum daily, 60 cfs May 19, 1934.
Maximum stage, 15.3 ft, from floodmark (original datum), about May 10, 1904 (discharge, 9,250 cfs).
-------
TABLE 4.3 (continued)
REMARKS: Records good. Since 1919, flow regulated by Upper Klamath Lake (see station 11507000). Diversions for
irrigation above station. Lost River diversion canal records and Lower Klamath Lake diversion canal and
pumpage records, furnished by Bureau of Reclamation, were discontinued in 1968.
(a) from Phillips, 1969
(b), (c), (d) from U. S. Geol. Survey, 1976
to
*»
-------
and at southern Klamath Lake and Tule Lake, in California.
Almost all public water supplies in the basin are obtained from
ground water.
Surface Water Quality—
Water quality in the larger streams and springs of the
basin is good to excellent, low in suspended sediment and dis-
solved solids. It is of calcium magnesium type. In general,
the dissolved solids concentration and hardness increase from
the Williamson River downstream to Keno, due to evaporation in
excess of precipitation, to addition of municipal and industrual
wastes, and to the return of drainage from irrigated lands and
marshes. Water chemical analyses from several locations in the
system are given in Table 4.4.
Sediment movement in streams is not great because much of
the inflow is from springs and also because the streams have low
gradients through most of the system. However, the water which
passes through Klamath Marsh, Agency Lake, Upper Klamath Lake
and other smaller marsh areas often has a brownish color and
considerable suspended organic matter derived from decaying
marsh vegetation and from algae and diatom blooms that occur
annually in Upper Klamath Lake. In addition since Upper Klamath
Lake i$ undergoing eutrophication, during late summer a strong
odor of putrefaction is evident around the lake shore.
4-4.2 Ground Water
Water Bearing Units--
Four main aquifer units have been distinguished in the
Klamath Basin (Illian, 1970) (Table 4.5). These units are
accepted here, although Sammel (1976) has proposed some changes
in nomenclature and has split some of Illian's units. Three of
these units crop out within the project area. The fourth is
present in the subsurface but is not known to have been pene-
trated by a well in the basin.
The sedimentary aquifer is distributed throughout the area
but is of significant thickness only in the lowlands. It is
composed of alluvium, terrace materials, Pleistocene-Holocene
lake deposits, Pliocene-Pleistocene lake deposits and their
locally lithified equivalents. Illian (1970) included some of
the youngest basalt flows (Qb), as well as Holocene Mazama Ash,
in this assemblage. Data on the productivity of water wells
completed in this unit indicates that specific capacities range
from 0.12 to 62 Ipm/m (0.01 to 5 gpm/ft) of drawdown and average
about 5.6 Ipm/m (0.45 gpm/ft). A black sand or gravel layer
encountered in this interval may yield from 25 to 125 Ipm/m (2
to 10 gpm/ft). These values are low and suggest near-imper-
meability. However, these sedimentary beds often yield suffi-
cient quantities of water for domestic purposes.
247
-------
TABLE 4.4 CHEMICAL ANALYSES OF SURFACE WATFRS, 1959-63 AVERAGES (Oregon State
Sanitary Authority, 1964)
Station1
K-l
K-2
K-3
K-4
K-5
K-6
K-7
pH
field
7.
7.
7.
8.
7.
7.
7.
7
5
5
1
9
9
7
T
O
11
8
10
11
11
11
11
• i
n
.8
.0
.3
.5
.7
.1
D.O.
me/ 8.
9.8
10.3
9.5
9.7
7.5
7.8
9.6
B.O.D.
1.1
1.3
1.7
5.4
4.4
4.5
3.0
so4
4.7
7.1
6.4
8.5
18.5
35.1
29.3
Cl
3.0
3.6
3.6
4.2
5.4
7.9
6.0
P04
0.13
0.18
0.17
0.11
0.22
0.29
0.24
NH3-N
0.51
0.33
0.42
0.61
0.99
0.97
0.50
N03-N
0.09
0.12
0.10
0.17
0.18
0.25
0.39
TS 2
121
107
114
141
162
221
194
S S 3
23
11
15
27
25
32
27
Alk.
44.5
34.6
38.2
47.2
57.7
74.2
71.8
Hard.
35.8
"25.4
30.7
34.9
42.5
71.9
67.0
Na
8.4
9.1
9.0
9.8
9.3
20.5
18.2
K
2.4
2.1
2.1
2.3
2.8
3.9
3.4
F
0.12
0.21
0.17
0.24
0.31
0.30
0.24
Cond.
UMHOS
CM
98
75
82
96
136
231
214
Station Locations
K-l Sprague River bridge near Chiloquin
K-2 Williamson River bridge one mile north of Chiloquin
K-3 Williamson River at old Highway 97 bridge
K-4 Link River at Fremont Bridge in Klamath Falls
K-5 Klamath River at Highway 97 bridge in Klamath Falls
K-6 Klamath River bridge at Keno
K-7 Klamath River below Copco's Big Bend powerhouse
T S = total solids
3S S = suspended solids (thus, IDS = T S -SS)
-------
TABLE 4.5 AQUIFER UNITS OF KLAMATH BASIN
Unit Name
Sedimentary
Aquifer
Corresponding
geologic map-
unit symbols
(fieure 1)
Ql, Qal, Qf,
1st, Tpt,
Qtb
Lithologic
Composition
Sand, silt,
clay , gravel
and their
lithified
equivalents ;
basalt
Water-
bearing
Charac-
teristics
Poor
Corresponding
Units from
Sammel (1976)
1. Alluvial Ter-
race deposits
2. Pleistocene and
Holocene lake
deposits
3. Quaternary
basalt
4. Older lake
deposits
5. Yonna Forma-
tion
Volcanic
Centers
Aquifer
Lower
Basalt
Aquifer
Volcanic
Ash
Aquifer
QTvcb
QTvc
Ttf (deep
subsurface;
not present
on figure 1)
Lava flows Mod.
and cinders to
(mostly High
basaltic)
Basalt High
Volcanic ash Poor
and sediments
6. Quaternary/Late
Tertiary erup-
tive centers
7. Quaternary/Late
Tertiary basalt
249
-------
The Volcanic Centers Aquifer consists of basalt ash, cin-
ders, breccia and flows, which accumulated around local vents.
There are numerous exposures of these eruptive centers in moun-
tain ridges, and many small ones probably are buried beneath the
valleys. The water-yielding characteristics of this unit are
generally excellent, reflecting the porous nature of the brec-
cias and cinders. However, wells in this unit show a wide range
of specific capacity, from less than 12 to over 1,240 Ipm/m (1 to
100+ gpm/ft). Stratigraphically, this aquifer unit is discon-
tinuous and local and may be overlain or truncated by the
younger Sedimentary Aquifer. Locally, it may be in intrusive
contact with older portions of the Sedimentary Aquifer.
The Lower Basalt Aquifer unit is composed of basalt flows
and minor interflow cinder zones. It underlies the Pliocene-
Pleistocene lacustrine sequence mapped as (Qts) on the geologic
map, but it may grade laterally into the lavas of the Volcanic
Centers Aquifer. It is the main aquifer unit in the Klamath
Basin. It is usually buried by 300 m (1,000 ft) or more of
sediments in the graben valleys and exposed in numerous low
hills. High permeability in fractured lavas and interflow
cinder zones gives the unit specific capacities which range from
400 to 6,200 Ipm/m (33 to 500 gpm/ft) with an average of about
1,800 Ipm/m (145 gpm/ft). Sammel (1976) estimated an average of
only 460 Ipm/m (37 gpm/ft) , but he admits that his figure is
based on rough estimates and sparse data. In this unit, average
permeability and specific capacity figures may not be meaning-
ful, because interflow cinder and scoria zones 3 to 14 m (10 to
45 ft) in thickness may provide nearly infinite permeability.
Lost circulation zones in this unit make deep drilling expensive
and hazardous.
Many water wells located near the edges of the major graben
valleys are completed in the upper part of this unit, but none
of them are known to have penetrated it completely. However, it
is likely that the Thermal Power Company deep geothermal explor-
ation well in the Klamath Hills (SW 1/4 sec. 35, T. 40 S.,
R. 9 E.), drilled to a total depth of 1,781 m (5,842 ft)/did
pass through this unit into the underlying Volcanic Ash Aquifer.
No details concerning this well have yet been released.
The Volcanic Ash Aquifer is believed to be composed of
thick acidic ash-flow tuffs, interbedded with minor flows,
palagonite tuff lenses and some fine-grained tuffaceous sedi-
ments. The assemblage is not exposed in the fault-block ridges
around the Klamath Basin, but it is projected under the basin
from distant outcrops both to the east and west. No water wells
are known to have penetrated this unit in the basin, but it is
likely to have been encountered in the Thermal Power Company
(Natomas Company) deep geothermal test in the Klamath Hills.
250
-------
Ground Water Flow—
"The Klamath Basin includes regional, intermediate and local
ground water flow systems. Relationships among these systems
are shown in Figure 4.5. The regional system receives recharge
from the Cascade Range on the west and from highlands on the
east, to the limits of the drainage basin in the Yamsay
Mountain-Gearhart Mountain and Quartz Mountain areas. This
water is believed to descend to depths greater than 3,000 m
(10,000 ft) below land surface under some areas of the Klamath
Basin. It is considered to discharge in wells and springs in
the Lower Klamath region, based on the high temperature gradi-
ents encountered in this area and the relatively high ionic
concentrations in these waters.
Water of local and intermediate flow systems also dis-
charges within the regional discharge area, having shorter
transit times and shallower depths of circulation. Therefore,
mixing can be expected to cause appreciable variation in water
temperatures and in chemical characteristics, reflecting differ-
ences in depth and time of circulation. This may-be observed
even in closely spaced wells. Waters of intermediate flow
systems fall between those of regional and local systems in
terms of temperature, flow pattern, chemical character and
degree of seasonal water level fluctuation.
Intermediate depth ground water flow systems in this region
are characterized by temperatures from 7°to 29°C (45° to 85°F),
and TDS varying from 100 to 800 mg/1, but averaging less than
200 mg/1.
Low temperatures and low TDS are characteristic of the
local flow systems. These waters have short, shallow circula-
tion paths and are often recharged and discharged within the
same aquifer or topographic feature.
Sammel (1976) has provided a fairly comprehensive listing
of wells in the central part of Klamath Basin.
Permeability—
Numerous water wells produce from the Sedimentary Aquifer,
the Volcanic Centers Aquifer and the Lower Basalt Aquifer.
Wells in the Sedimentary Aquifer in the flatlands adjacent to
the Klamath Hills typically yield less than 110 1pm (30 gpm).
This contrasts with the Lower Basalt Aquifer, reached at depths
of more than 210 m (680 ft), with yields up to 13,000 1pm
(3,500 gpm) with 25 m (83 ft) of drawdown (530 Ipm/m 143
gpm/ft]). Basalt and cinders are encountered in the Keno area
at depths of 3 to 45 m (10 to 150 ft). Production from this
unit varies from 27 1pm (7 gpm) with 18 m (60 ft) of drawdown,
to 75 1pm (20 gpm) with no observable drawdown. A well area
near Henley, close to the center of the basin, produces up to
251
-------
NJ
tn
to
REGIONAL
Figure 4.5 Salient features of local, intermediate and regional groundwater
flow systems. (Illian, 1970)
-------
3,800 1pm (1,000 gpm) from water-bearing gravels of the Sedi-
mentary Aquifer, which here is over 380 m (1,250 ft) thick.
Closer to the hills, the Volcanic Centers and Lower Basalt
Aquifers are intercepted at from 90 to 180 m (300 to 600 ft).
Recharge and Discharge—
Ground water recharge occurs in the Cascade Mountains west
of the basin and in upland areas to the east and north of the
basin, where heavy precipitation occurs over areas of permeable
soil or fractured volcanic rocks. Few water wells have been
drilled in the recharge areas. Those that exist produce water
of low TDS and low temperature.
The Klamath Basin has been divided into four sub-basins
(Illian, 1970). Of these, only the southwestern corner of the
Upper Klamath Lake and the Lost River sub-basins are of concern
here.
The Upper Klamath Lake sub-basin is bounded on the west by
the crest of the Cascade Mountains and on the east by Chiloquin
Ridge and Naylox Mountain. It extends southward approximately
to Link River and Klamath Falls.
Based on climatological, soils and evapotranspiration
data, it is estimated that about 99,000 ha-m (800,000 acre-ft)
of water per year is recharged to the ground water system in
this sub-basin. Water wells in the area are not abundant; water
levels are generally shallow. Some artesian wells report pres-
sures to .67 kg/sq cm (9.6 psi) indicating a piezometric level
6.7 m (22 ft) above land surface. The highest reported pro-
duction is from the Lower Basalt Aquifer, which yields 4,500 1pm
(1,200 gpm) with 28 m (92 ft) of drawdown 137 Ipm/m (11 gpm/ft).
Water temperatures range from 8°to 11°C (47°to 51°F).
The Lost River sub-basin covers 7,820 sq km (3,019 sq mi)
in the southern portion of the Klamath Basin. Of the total,
3,405 sq km (1,315 sq mi) are in Oregon and 4,410 sq km (1,704
sq mi) are in California. The ground water boundaries approxi-
mately follow topographic divides.
It is estimated that the total average annual ground water
recharge in this sub-basin is about 111,000 ha-m (900,000
acre-ft). This consists of 67,800 ha-m (550,000 acre-ft) of
recharge from adjacent highlands, 24,700 ha-m (200,000 acre-ft)
of underflow from the Upper Klamath Lake and 18,500 ha-m
(150,000 acre-ft) of underflow from the Sprague River sub-basin
to the east.
253
-------
4.4-3 Hydrologic Budget
The outline of the ground water basin is essentially the
same as that of the surface water drainage system and has an
area of about 14,800 sq km (5,700 sq mi). Precipitation within
this area varies from about 380 mm (15 in) on the valley floors
to over 1,500 mm (60 in) in the upper parts of the Cascade
Range, along the western boundary of the basin. Precipitation
is estimated to supply a total inflow of about 826,000 ha-m
(6.7 million acre-ft) of water to the basin each year. The
complete water budget for the basin is:
Precipitation +8.264 x 10s ha-m (6.700 x 106 acre-ft)
i
Evapotranspiration -6.227 x 105 ha-m (5.048 x 106 acre-ft)
Pumped Ground Water - 0.428 x 105 ha-m (0.347 x 106 acre-ft)
Ground Water Outflow - 0.123 x 105 ha-m (0.100 x 106 acre-ft)
Surface Water Outflow -1.486 x 105 ha-m (1.205 x 106 acre-ft)
TOTAL: 0 0
The sum of pumped ground water and ground water outflow
represents total withdrawal from the regional system. For pur-
poses of this discussion, it is assumed to be in balance with
recharge via infiltration of precipitation. Increases in well
pumpage should be matched regionally by decreases in ground
water outflow from the system. Local deficits, however, may be
significant and may show up as lowered piezometric levels in
wells.
4.5 CHEMICAL CHARACTERISTICS OF GROUND WATER
Klamath Basin ground waters fall into two main chemical
groups (Table 4.6). Cool wells and springs are of the calcium
magnesium bicarbonate type, with low TDS. In these waters, TDS
averages about 100 ppm, with bicarbonate concentrations of about
50 ppm. Sodium may be equal to or less abundant than calcium or
magnesium in concentration, frequently being less than 10 ppm.
Magnesium is more abundant than potassium, with both generally
present in concentrations less than 5 ppm. Silica is present in
concentrations of about 25 ppm. Chloride and suIfate have very
low concentrations (<10 ppm). Relative ion abundances may be
given as calcium ^ sodium ^ magnesium > potassium and bicar-
bonate ^ sulfate S chloride.
254
-------
TABLE 4.6 CHEMICAL ANALYSES OF WATERS FROM SPRINGS AND WELLS
l-o
Ul
Name of Spring or Well
Eagle Point Spring
Shell Rock Spring
Cabin Spring
Hummingbird Spring
Neubert Spring
Well, 98.6 feet deep
OIT Well #6
Mer-Bell-Dairy
J. E. Ericson
Oregon Water Corp.
Keno Spring
Alfred Jacobson
Weyerhaeuser Well #4
U. S. Air Force
Dave O'Connor
0. H. Osborn
Anderson Well
Abe Boehm
Liskey Well
Tulana Farms Spring
Sample
Location
T, R, Sec.
36-7-23dca
38-8-27
37-8-26
37-9-6bcd
37-9-7adc
37-9-9dcc
38-9-20adb
38-9-28ccc
38-9-28cdc
38-9-30acb
38-12-14
39-9-34
39-9-18
40-7-llccc
40-9-23bab
40-9-27cda
40-9-27
40-9-28aca
40-9-34aca
41-8-5cbb
Date
of
Sample
4-6-75
8-6-75
8-5-72
4-2-75
8-6-75
8-6-75
3-31-75
1-24-55
2-19-55
8-8-75
10-16-75
5-20-74
10-11-73
5-27-74
5-7-74
5-31-74
11-8-75
5-30-74
5-9-74
8-8-75
Temp. ,
°C
85
7
11
11
10
10
79
81
83
15
11
30
22
15
24
90
27
25
93
13
PH
8.3
6.4
5.5
8.3
8.2
6.8
8.2
8.8
8.7
8.0
7.7
7.6
8.3
8.6
7.6
9.5
8.0
7.1
8.9
6.9
Specific
Conduc-
tance
y/cm
305
110
-
135-
160
150
1050
1160
1230
250
100
290
200
340
260
920
450
2700
1030
115
TDS
Evapo-
ration
—
_
—
-
158
_
_
_
-
72
_
_
^
-
286
_
724
_
-------
TABLE 4.6 (continued)
Concentrations (milligrams per liter)
Ui
Name of Spring or Well
Eagle Point Spring N
Shell Rock Spring
Cabin Spring
Hummingbird Spring
Neubert Spring
Well, 98.6 feet deep
OIT Well //6
Mer-Bell-Dairy
J. E. Ericson
Oregon Water Corp.
Keno Spring
Alfred Ja'cobson
Weyerhaeuser Well //4
U. S. Air Force
Dave O'Connor
0. H. Osborn
Anderson Well
Abe Boehm
Liskey Well
Tulana Farms Spring
Si02
38
32
29
18
21
24
31
81
87
27
40
65
16
31
42
90
41
100
90
24
Na
62
5.9
5.9
8.0
7.0
7.6
195
213
221
22
4.1
69
32
17
32
140
88
480
200
5.7
K
5.7
1.5
1.6
1.2
1.2
1.3
3.9
4.2
4.4
-
3.0
12
3.3
1.6
8.1
4.1
2.5
18
4.0
1.2
Ca
0.6
8.1
11.2
9.2
10.6
12.1
24.2
23
25
14.4
7
160
10
24
12
15
5.0
180
15
9.2
Mg
0.1
3.9
5.1
6.5
8.2
7.2
0.1
0
0
0.8
6.2
2.4
1.9
17
6.6
0
0.1
47
0.1
4.9
HC03
136
50
94
84
96
94
44
32
32
-
73
160
115
200
130
37
165
1460
48
60
C03
0
0
0
0
0
0
0
8
8
-
0
0
4.5
3
0
9
6.0
1
2
0
so4
<2
<2
<1
<2
<2
<2
400
403
1.2
0.4
13
4
2.3
14
270
36.2
300
360
2
•"
Cl
16
<1
<2
1
1
1
58
54
56
4.5
1.8
7.9
4
2.3
9.1
56
23
170
59
1
F
.75
.10
.10
.10
.10
.11
1.45
1.2
1.6
.01
.08
.10
.11
0
0
1.5
.40
.20
1.5
.07
B
.14
.05
.10
.07
.05
.05
1.0
.96
.91
-
.05
.50
.09
0.9
0
.77
.15
1.4
.65
.05
-------
TABLE 4.6 (continued)
to
en
-J
Name of Spring or Wei
Eagle Point Spring
Shell Rock Spring
Cabin Spring
Hummingbird Spring
Neubert Spring
Well, 98.6 feet deep
OIT Well //6
Mer-Bell-Dairy
J. E. Ericson
Oregon Water Corp.
Keno Spring
Alfred Jacobson
Weyerhaeuser Well #4
U. S. Air Force
Dave O'Connor
0. H. Osborn
Anderson Well
Abe Boehm
Liskey Well
Tulana Farms Spring
] Na:K
18.51
6.70
6.30
9.95
9.96
1.70
85.1
86.50
76.80
16.98
2.32
9.78
16.40
18.07
6.72
7.88
59.70
45.35
75.00
8.10
Na:Ca
180.99
12.70
0.90
1.15
1.10
1.51
14.05
16.20
15.40
2.66
1.02
.75
5.58
1.23
4.65
2.21
30.80
4.65
16.13
1.08
Na+K
Ca+Mg
149.60
.82
.50
.55
.61
1.08
14.12
16.40
15.61
1.33
.59
.81
4.51
.60
2.80
2.49
30.71
3.32
14.81
.65
bJ.:
Total
Alk.
.40
.07
.10
.04
.04
.04
4.53
4.63
-
-
.06
.17
.12
.04
.24
4.19
.46
.40
3.64
.06
Cl
so4
21.70
1.36
-
1.35
1.35
2.72
.39
.36
.35
10.0
12.18
1.64
2.71
2.71
1.76
.56
1.72
1.53
.52
.50
— JLOIIIC na
Cl
F
11.45
5.42
-
5.42
4.94
39.40
21.44
24.10
18.80
239.50
21.85
42.20
19.78
-
-
20.01
32.80
'455.48
18.40
7.83
CJ.US —
Cl
B
34,87
6.80
-
7.63
7.63
-
17.70
17.16
18.78
-
10.97
4.82
13.56
.08
-
22.19
46.91
37.05
28.17
6.10
HC03
B
172.31
177.38
269.60
340.56
333.47
-
7.80
7.39
7.80
—
259.50
56.76
235.52
400.08
-
10.06
194.20
185.11
15.40
212.85
Alk
so4
53.61
19.71
-
62.02
37.06
72.39
.09
.08
.07
—
200.10
9.70
23.55
69.54
7.31
.13
3.72
3.83
.14
9.72
-------
The second type of water, occurring in warm and hot wells
and springs, mostly within basins of the Klamath graben, is a
sodium bicarbonate chloride sulfate water. TDS in these waters
are as high as 4,000 ppm (Sammel, 1976) but average about
700 ppm. The bicarbonate ion is relatively less abundant than
in cold water but still may exceed 100 ppm. Sulfate and chlor-
ide concentrations characteristically are above 50 ppm. The
concentration of boron and fluorine increases with temperature.
The relative abundance of cations is sodium > calcium > potas-
sium > magnesium. Sodium concentrations in the hottest wells
may be several hundred ppm. The pH of the waters ranges from
8.5 to 9.5. They are more alkaline than the cold waters of the
basin, which range from neutral to mildly alkaline. Silica
concentrations reach and locally exceed 100 ppm.
4.5.1 Chemistry of Thermal Waters
Water chemistry data is useful in estimating reservoir
temperature, fluid state and fluid migration history.
If calcium bicarbonate type waters enter the regional
circulation system in recharge areas and descend to depths
where temperatures are 80° to 120°C (175° to 250°F) or higher,
their composition will change. Characteristically, the change
involves an increase in sodium and potassium, derived from the
hydration of silicate minerals such as feldspar. Calcium and
especially magnesium are likely to decrease in concentration
somewhat, due to the decreased solubility of carbonate minerals
in water with increasing temperature; in any case, they show
depletion relative to sodium.
The magnitude of these changes depends on the validity of a
number of assumptions: temperature-dependent reactions actually
take place at depth; all of the cation constituents are suffi-
ciently abundant at depth; water-rock equilibration occurs at
reservoir temperature; no re-equilibration takes place as the
water returns to colder regions; and the hot, mineralized waters
do not mix appreciably with cooler meteoric or shallow ground
water; also, there are no evaporite beds at shallow depth to
yield ions to low temperature solubility reactions.
Most high temperature waters of the Basin and Range and
Lava Plateau Provinces exhibit, to varying degree, characteris-
tics of deep circulation. However, most thermal waters of the
Klamath Basin show larger amounts of calcium than potassium, and
high ratios of sodium to potassium. Therefore, something may
retard the solution of potassium in waters of this area; or
these waters may be diluted on a large scale by cold meteoric
water; or the subsurface temperatures may be lower than the 80°
to 120°C (175° to 250°F) range at depths of 2 to 3 km (6,500 to
10,000 ft). Sammel (1976) discussed calcium to magnesium and
bicarbonate plus carbonate to chloride ratios in Klamath Basin
258
-------
waters. This and other chemistry indicates that spring and well
waters having temperatures greater than 65°C (149°F) are not
significantly diluted with cold water but have been cooled
mainly by conduction.
Cool meteoric waters generally exhibit the following anion
balance: bicarbonate > sulfate g chloride. Heating of this
water as it descends into deep aquifers results in a change in
the balance as follows: sulfate £ chloride > bicarbonate. In
thermal waters of the Klamath Basin, sulfate and chloride con-
centrations increase both absolutely and relative to bicarbon-
ate, but not in proportion to increasing temperature. This sup-
ports the idea of relatively low temperature equilibration at
depth, as suggested by the cation ratios. The chloride-rich
waters of the Klamath Hills area appear to have cooled while
retaining chloride concentrations representative of higher
temperatues, along a unique dilution trend (Sammel, 1976).
Silica concentrations may be used to determine reservoir
temperatures (Fournier and Rowe, 1966). Temperature calcula-
tions require designation of either amorphous (chalcedony) or
crystalline quartz as the source of silica; usually, this is
problematic. Also, siliceous rocks characteristically yield
more silica and higher ratios of silica to other species than do
basic rocks. These factors affect silica geothermometry in
Klamath Basin, where a variety of rock types is present, in-
cluding diatomite, palagonite and basalt at shallow depths, and
acidic ash-flow tuffs at greater depths.
Generally, silica concentrations in Klamath Basin thermal
waters are moderate (50 to 118 ppm). With this range of values
for silica, and assuming equilibration with chalcedony, temper-
atures at depth are calculated to be in the range from 120° to
150°C (250° to 300°F), by the method of Fournier and Rowe
(1966).
The chloride content of water has been established as a
reliable indicator for distinguishing hot water from vapor-domi-
nated systems (White, et al., 1971), as well as for indicating
distance and duration of flow. In general, very low chloride
concentrations in hot springs and shallow wells characterize
vapor-dominated systems at depth, whereas chloride concentra-
tions above 50 ppm in thermal waters tend to characterize hot
water systems. Cool water associated with evaporite deposits or
connate water in marine formations may contain more than 50 ppm
chloride. However, evaporites are not known to occur here, and
the only marine formation still likely to contain connate water
is the upper Cretaceous sequence of unknown subsurface distri-
bution and depth. Thermal waters in the Klamath Basin tend to
have chloride concentrations of 50 ppm or above. Therefore, a
hot water rather than a vapor-dominated system is expected here.
259
-------
Other ions can have significance in the interpretation of
geothermal conditions. Among these, ammonia, boron, mercury,
carbon dioxide and sulfur compounds in thermal waters may indi-
cate subsurface boiling and consequent enrichment of volatiles
in springs and wells. Of these constituents, trace amounts of
mercury are present in the altered rocks of both Klamath Hills
and Klamath Falls. Boron is nearly absent from cooler waters of
the region but is present in higher concentrations in the
thermal waters at Klamath Falls. However, the concentration of
boron relative to chloride is not high and does not, therefore,
suggest vapor transport of boron from an underlying reservoir.
Fluoride in thermal waters may derive from the breakdown of
mica and hornblende in igneous rocks, from the presence of
primary magmatic gases or from the solubility of fluoride. High
fluoride concentrations are common in water from regions of
young igneous activity; however, due to the variety of possible
sources of the ion, its abundance does not indicate a magmatic
source. Relatively high fluoride concentrations characterize
thermal waters at Klamath Falls and the Klamath Hills. However,
in the absence of other evidence, fluoride abundance is not
interpreted to indicate a magmatic source.
Two main water types are present in the area; concentra-
tions of silica, sulfate, sodium and chloride differ systemat-
ically between them. Cold waters in upland recharge areas, and
in shallow circulation zones below, constitute one type. TDS of
these waters is low and the predominant ions are calcium and
bicarbonate.
The second water type comprises thermal springs and wells
in the area, which are discharge points in the regional circula-
tion pattern and are on or near known or inferred fault zones.
Deep circulation has carried these waters through Tertiary
tuffs, lavas, and breccias, and they are characterized by rela-
tively high TDS. Composition varies, but the most abundant ions
generally are sodium and sulfate, with moderately abundant
chloride. Silica, fluoride and boron also are relatively abun-
dant. A tentative conclusion is that the maximum reservoir
temperature, based on both the silica and alkali geothermo-
meters, is 120° to 150°C (250° to 300°F) at depths of 1 to
1.5 km (3,300 to 5,000 ft) and 160° to 180°C (320° to 355°F) at
depths of 2.5 to 3 km (8,000 to 10,000 ft). A few cool waters
of high alkali content may be explained by ion exchange with
clay minerals of near-surface rocks and/or selective yielding of
sodium and potassium from devitrification of silica and alkali-
rich tuffs, such as the surficial Mazama Pumice. Abundant
silica also probably results from leaching of low temperature
chalcedony in devitrified silicic tuffs and diatomaceous
sediments.
260
-------
The absence of well data from deeper than 600 m (2,000 ft)
prevents a definitive statement for the central Lower Klamath
Basin. Therefore, the thermal and geochemical anomaly patterns
do not conclusively evaluate the potential in the basin, partic-
ularly not at depths greater than a few tens of meters.
Although a hot water aquifer of mild salinity is likely, the
water chemistry does not exclude a saline hot water aquifer or
even a steam-bearing deeper horizon that heats the shallow
aquifer through upward leakage along faults. - *
4.6 SEISMICITY
4.6.1 Historical Seismicity
Most of Oregon and adjacent parts of Idaho, Nevada and
California form a large region of low seismicity, in comparison
with many parts of the western United States. Historically, no
major, destructive earthquakes have occurred in Oregon, nor has
any instance of surface faulting been reported. Moderate seis-
micity characterizes the Portland-Willamette Valley area of
northwestern Oregon; however, the rest of the state exhibits
lower or negligible seismicity (Fig. 4.6). Slight seismicity
has been reported near Klamath Falls but not elsewhere in
Klamath Basin. Berg and Baker (1963) reported five small
shocks, with intensity IV, at Klamath Falls during the years
1947 to 1951.
Throughout the Pacific northwest, including Klamath Basin,
very few seismograph stations operated until the year 1962;
earthquakes of magnitude smaller than 4.5 to 5 either were not
recorded at all or were not recorded at sufficient stations to
permit instrumental location of epicenters and determination of
Richter magnitude. Thus, nearly all pre-1962 shocks were loca-
ted using felt-reports, which are highly dependent upon the
distribution of population and time of day of occurrence. Also,
the "size" of these events was rated on intensity scales, which
are crude, graduated ratings of megascopic earthquake effects,
such as kind and degree of shaking or of damage to buildings.
Therefore, the earthquake history of this region is poorly
known as to the occurrence or non-occurrence, epicenter location,
and size of smaller shocks (M^ 5). For this reason, correlation
of seismicity with particular faults and determination of magni-
tude-frequency curves for various areas cannot be done with much
confidence.
4.6.2 Seismic Risk
Earthquake risk is poorly known in most of Oregon and
northernmost California because of the extremely low seismicity
and inadequate reporting of such shocks as have occurred.
261
-------
47°
46°
45"
44°
43°
42'
124" 123" 122° 121° 120° 119" 118° 117°
~~1 I I I I I I T~
EARTHQUAKE EPICENTERS IN OREGON
1841 - 1970
47°
46"
45'
44.
43'
42'
124° 123° 122'
121'
120° 119'
118° 117'
Figure 4.6 Earthquake epicenters in Oregon, 1841-1970.
(Couch and Lowell, 1971).
262
-------
Nevertheless, it may be useful to review the sparse statistics.
Couch and Lowell (1971) have analyzed earthquake occurrence in
Oregon and described the seismicity of several physiographic
provinces. One of the provinces is the Basin and Range, which
includes Klamath Basin.
Very limited data suggests a rate of energy release of
8.8 x 1016 ergs/yr for the period 1870 to 1970 (Couch and
Lowell, 1971); this figure is probably too low, as ^tftie lack of
any reported shocks for 1870 to 1906 is highly dubious. In any
case, this rate of energy release is equivalent to the occur-
rence of one magnitude 3.3 earthquake per year per 10,000 sq km;
or to one shock of M^5 per 50 years per 104 sq km. This occur-
rence rate has been used, along with an assumed "b-slope" of
1.0, to draw the magnitude-frequency curve in Figure 4.7
Clearly, this area has exhibited very low seismicity. Compare
the seismicity of central coastal California, which may be
expressed as ten MS 5 shocks per 50 years per 104 sq km.
Based upon the above data, the maximum probable earthquake
acceleration per 100 years at a given site in the Klamath Basin
is expected to be about 0.07 g. Therefore, earthquake risk to
well-engineered facilities in this area is quite low in compari-
son with many other areas, particularly coastal or southern
California.
4.6.3 Seismicity and Tectonism
As already noted, earthquake epicenters for most of the
period of record (i.e., before 1963) are inaccurately located.
Couch and Lowell (1971) estimate that epicenters located from
felt-data in the sparsely populated area east of the Cascades
have a probable error of 13 km (8 mi); this seems optimistic
because the location errors are probably greater. From 1963 to
1971, no instrumentally located shocks occurred in Klamath Basin
(Couch and Lowell, 1971). Therefore, available data does not
permit correlation of epicenters and faults nor definition of
seismically active faults.
Focal mechanism studies by Couch and McFarlane (1970) and
Dehlinger, et al. (1963) show a regional stress field that has
minimum compressive stress axis oriented east-west, and maximum
compressive stress axes in a vertical, north-south plane. This
fits a pattern of north-south trending normal faults, and over-
all east-west extension, as well as right-lateral strike-slip on
northwest trending faults.
Therefore, the regional stress field does not fit Klamath
Basin, dominated by northwest trending normal faults. This
disagreement has two obvious possible explanations:
263
-------
.1-
CJ
JC
*O
oc.
UJ
LJ
X .01-
§
o
h-
o:
LJ
L.
o
a:
LJ
CD
z
.001-
\
_\
: \
: \
: \
\ DATA POINT F
\ / AND LOWELL
*
\
: \
; \
\tp
^
\
^
• \
: \
: . . \
ROM COUCH
(1971)
MAGNITUDE
Figure 4 . 7
Magnitude vs frequency of occurrence for earthquakes
in the Basin and Range Physiographic Province of
southern Oregon^
264
-------
(1) The present stress field does not characterize that of
late Tertiary and Quaternary time in this region.
2) Young faulting in the Klamath Basin was primarily the
result of volcanic subsidence causing reactivation of
much older, strike-slip faults.
The second explanation is preferred for two reasons:
1) it does not require a radical change in the stress^field, and
2) it fits the observation that late Quaternary fault movements
and present-day seismicity are very minor in this region, and
that major faulting seems to have been closely associated, in
both space and time, with Plio-Quaternary volcanism.
265
-------
REFERENCES
Berg, J. W.,and C. D. Baker. Oregon Earthquakes, 1841 through
1958. Bull. Seism. Soc. Am., v. 53, p. 95-108, 1963.
Callaghan, E., and A. F. Buddington. Metalliferous Mineral
Deposits of the Cascade Range in Oregon. USGS Bull. 893,
141 p., 1938.
Couch, R. W., and R. P. Lowell. Earthquakes and Seismic Energy
Release in Oregon. Oregon Dept. of Geol. and Min. Ind.,
The Ore Bin, v. 33, no. 4, p. 61-84, 1971.
Couch, R. W.,and W. T. McFarlane. A Fault Plane Solution of the
October, 1969 Mount Rainier Earthquake and Tectonic Move-
ments in the Pacific Northwest from Fault Plane and First
Motion Studies (abs.). Trans. Am. Geophys. Un., v. 52,
1970.
Dehlinger, P., et al. Investigations of the Earthquake of
November 5, 1962, North of Portland. The Ore Bin, v. 25,
p. 53-68, 1963.
Fournier, R. 0., and J. J. Rowe. Estimation of Underground
Temperatures from the Silica Content of Water from Hot
Springs and Wet-Steam Wells. Am. J. Sci., v. 264, p.
685-697, 1966.
Hanna, G. D., and G. C. Gester. Pliocene Lake Beds Near Dorris,
California. Calif. Acad. Sci. Occ. Papers 42, 1963.
Hardyman, R., J. R. Mclntyre and L. K. Richardson. Geologic Map
of the Southern Klamath Basin. USGS Open File Map, 1972.
Illian, J. P. Interim Report on the Ground Water in the Klamath
Basin, Oregon. Report of the Oregon State Engineer, Salem,
Oregon, 1970.
Leonard, A. R.,and A. B. Harris. Ground Water in Selected Areas
in the Klamath Basin, Oregon. Oregon State Engineering
Ground Water Report No. 21, 1974.
266
-------
Lund, J. W., G. G. Culver and L. S. Svanevik. Utilization of
Geothermal Energy. Proc. of the International Conference
on Geothermal Energy, Oregon Institute of Technology,
Klamath Falls, Oregon, 1974.
Newcomb, R. C. and D. N. Hart. Preliminary Report on the Ground
Water Resources of the Klamath River Basin, Oregon. USGS
Open File Report, 1958.
. *•
Oregon State Sanitary Authority. Quality of Klamath Basin
Waters in Oregon, July 1959 to December 1963, 1964.
Pacific Northwest River Basins Commission Meteorological Com-
mittee. Climatologic Handbook, Columbia Basin State,
1968-1969.
Peterson, N. V., and E. A. Groh. Geothermal Potential of the
Klamath Falls Area, Oregon: A Preliminary Study. Oregon
Dept. Geol. and Min. Ind., The Ore Bin, v. 29, no. 11, p.
209-231, 1967.
Peterson, N. V., and J. R. Mclntyre. The Reconnaissance Geology
and Mineral Resources of Eastern Klamath and Western Lake
County, Oregon. Oregon Dept. Geol. and Min. Ind. Bull. 66,
1970
Phillips, K. N. Water Resources and Development; in Mineral and
Water Resources of Oregon, A. E. Weissenborn, Principal
Investigator, Oregon Dept. Geol. and Min. Ind. Bull. 64,
1969.
Sanunel, E. A. Hydrologic Reconnaissance of the Geothermal Area
Near Klamath Falls, Oregon. USGS Open File Report 76-127,
1976.
Sass, J. H., and E. A. Sammel. Heat Flow Data and Their Relation
to Observed Geothermal Phenomena near Klamath Falls,
Oregon. J. Geophys. Res. v. 81, no. 26, p. 4863-4868,
1976.
U.'S. Geological Survey. Surface Water Supply of the United
States, 1966-1970, Part II, Pacific Slope Basins in Cali-
fornia. USGS Water Supply Paper 2129, 1976.
Wells, F. G- Geology of the Medford Quadrange. USGS Map Q 89,
1956.
White, D. E., L. H. P. Muffler and A. H. Truesdell. Vapor-
dominated Hydrothermal Systems Compared with Hot Water
Systems. Econ. Geol., v. 66,,p. 7597, 1971.
267
-------
Williams, H. Geology of the MacDoel Quadrangle, California.
Cal. Div. Mines and Geol. Bull. 151, 78 p., 1949.
268
-------
SECTION 5
RIO GRANDE RIFT ZONE
5.1 INTRODUCTION
This section presents baseline data on climatology, geol-
ogy, hydrology and seismology to aid in assessment of environ-
mental impacts of potential geothermal development in the Rio
Grande Rift Zone, New Mexico. Aspects of climatology, geother-
mal characteristics, geology, hydrology and chemical character-
istics of ground water are discussed. Seismicity of New Mexico,
of the Rio Grande Rift and of the Valles Caldera region is also
described.
5.1.1 Summary
For this report, the Rio Grande Rift in New Mexico runs
from the Colorado border on the north to the border with Texas
and Mexico on the south and has a variable width limited by
geologic structures. It includes the valley of the Rio Grande
itself and all or part of the closed basins bordering the Rio
Grande Valley. Climate and vegetation in the rift vary with
altitude and latitude. The low southern river valley is a lower
Sonoran desert with 180 mm (7 in) average annual precipitation,
1,780 mm (70 in) average annual evaporation, and a mean annual
temperature about 16°C (60°F). The high northern mountains
range from Canadian zone forests to arctic tundra, with up to
810 mm (32 in) average annual precipitation, 1,020 mm (40 in)
average annual evaporation, and a mean annual temperature about
4°C (40°F).
Surface water and ground water both derive ultimately from
precipitation. The Rio Grande is the only large perennial
stream in the rift. The ground water surface or water table
usually follows the land surface contours. Both surface and
ground water are used for domestic, agricultural and industrial
purposes in the Rio Grande Rift. Agricultural water usually
comes from surface water diversions. Municipal and industrial
users mostly rely on ground water.
Geology of the rift is complex. Older rocks, generally
Precambrian to Cretaceous in age, occupy the uplifted blocks.
Younger sediments, mostly Tertiary and Quaternary in age, fill
the downdropped troughs. Complex folding in the mountains and
269
-------
discontinuous faulting throughout the rift make the geologic
structure difficult to interpret. A series of subparallel
faults bounds the rift. The discontinuous nature of the graben-
forming faults allows a great variety of interpretations and
leads to major variations in the width of the rift zone.
Seismicity of the rift area may be evaluated from historic
earthquake reports, instrumental data from earthquakes and
microearthquakes, and faulting of geologically recent.geomorphic
features. These methods agree in general that the area of
greatest seismic activity is near Socorro. The predicted maxi-
mum shock in a 100-year period varies widely with the data
used to evaluate seismic risk. Historic records show the
highest level, a magnitude 6 shock; instrumental data from
microseisms show the lowest level, a magnitude 4.6 shock.
5.1.2 Background
This report integrates reports published on the geology,
hydrology, climatology, and seismology of the Rio Grande Rift
Zone in New Mexico. It provides the background for preparation
of an assessment report on the possible environmental impact of
geothermal development in the Rio Grande Rift. The environ-
mental impacts that will be considered include ground water
pollution, seismic activity and subsidence potential.
Hundreds, perhaps thousands, of publications deal with some
aspect of the Rio Grande Rift. Numerous government organiza-
tions, schools, groups and individuals have published documents
concerning the area. For instance, the New Mexico Geological
Society began publishing its annual field conference guidebook
in 1950, and of the 27 guidebooks published, 15 contain articles
pertinent to the Rio Grande Rift. The New Mexico Bureau of
Mines and Mineral Resources lists over a hundred publications
that cover parts of the area. Sources have had to be chosen,
read and integrated in this report from among the hundreds
available, and that choice was often arbitrary. Most sources
used are readily available and cover a large area.
Definition of the rift caused another problem in sorting
data for use in this report. Most documents deal with the Rio
Grande Valley or the Rip Grande drainage basin. Each publica-
tion makes its own definition of the area included. The Rio
Grande Valley, as we use the term here, refers to the stream
valley of the Rio Grande itself and includes the drainage area
that contributes direct surface runoff (Fig. 5.1). The Rio
Grande drainage basin, as we use the term, includes all the
surface area that ultimately contributes to the flow of the Rio
Grande. The Rio Grande drainage basin, under this definition,
begins in Colorado and ends in Texas and Mexico where the river
enters the Gulf of Mexico. Several drainage sub-basins and
basins with interior drainage lie within this large Rio Grande
270
-------
WT;M=d
r*Sf*«-r*^
.v°.", i i ;-, "?-i'""i I i . i—i*v" s...J . ! -C-U-
-: ~--»^ue^xX
*' I H ^ . i . l« 1 ^ I
I "07 E R'O ']'
._..^._, 1 • "•"'•!
*-v-Tra'_-rr iH i ' ' ** i ' i
:H^tx=!
_ °'i"," __. "_
j^^-i^^"--^"
"•-' * i i
NEW MEXICO
'"•
;
.-: _J
DC
1
10V
i .• .-• 5- •! « ., ;
i - — "- • — -
106' '05- ,c«- 103
LEGEND
—^ 0«AIM*6E BASIN BOUNDARY
I IrtH GirtO LAND
Figure 5.1 Map of Rio Grande Valley and area of direct surface
runoff. (Anonymous, 1967)
271
-------
Basin (Figs. 5.2 and 5.3). Some of the basins with interior
drainage discharge ground water to the Rio Grande.
Geologic structures bound the Rio Grande Rift area on the
east and west sides. The structural geology is complex. The
rift may be interpreted as a narrow graben running the length of
New Mexico in about the same position as the Rio Grande Valley
(Fig. 5.4), or the Rio Grande Rift may be interpreted as a broad
series of related and subparallel troughs and horsts..
For this report, the Rio Grande Rift is defined as the part
of New Mexico that appears to be physically bounded by a series
of related subparallel faults and cross faults that form a
structural basin now occupied by the Rio Grande (Plate 5.1).
Because this definition is based on geologic structure, it
excludes some areas, such as the Pecos River Basin, which lie
within the Rio Grande drainage basin. Likewise, it includes
some areas west of the Rio Grande that lie outside the area of
direct surface runoff, such as the San Augustin Plains. By
considering only the area in New Mexico, this report also
excludes both the structural and hydrologic extensions of the
Rio Grande Rift Valley in Colorado, Texas and Mexico.
5.1.3 Climatology
Spanish colonization of New Mexico began in the sixteenth cen-
tury and sporadic collection of climatologic data began almost
immediately. Although systematic data collection began about
1850, few stations have continuous records.
Table 5.1 and Figures 5. 5 and 5.6 show average temperatures
and average precipitation values for several places in the Rio
Grande Rift.
The Rio Grande Rift extends roughly 645 km (400 mi) in New
Mexico, covering 5° of latitude and over 2,750 m
(9,000 ft) of altitude. These extremes combine to produce
climates ranging from low desert to alpine conditions. Vegeta-
tion types vary with altitude, latitude, and precipitation
(Figs. 5.7, and 5.8).
Generally, the incised river valley has lower precipitation
and higher evaporation than the more mountainous regions border-
ing it. The northern end of the rift has higher precipitation
and lower evaporation than the southern part. Average annual
precipitation ranges from 180 mm (7 in) in the far south and
incised Rio Grande Valley to about 810 mm (32 in) in the high
northern mountains. Water loss by evapotranspiration increases
southward along the rift zone. Average annual evaporation
ranges from about l,02D mm (40 in) in the north to about 1,780
mm (70 in) in the southern valley. Table 5.3 shows data from
several stations measuring evaporation in the Rio Grande Rift.
272
-------
—'—fr»..m ' "j j/i -c.>k-j i ,
i*tlTl ~'~J rJi"^-'-/-i—PTT
! <\ hf ' ' -1-4- ' ' ^T I ' '-rr-rd-H
'"r^^iTiT^^;/..!!
: " 1 i !
1-- tr^: : \ M F * 1
i . , , 1 , i^* 1
• u [ ' >D :
C 0
NEW M
• >~. i L
10»- 101* I07« I0i' JOS'
EXICO
»c 7. w ,,
fc^==d
104- 103
BASIN WITH EXTERNAL DRAINAGE
A, Rio Grande VUley
8, Pecos River Bosin
BASINS WITH INTERNAL DRAINAGE
I, Esloncio Basin 6, Salt Bosin
Z, North Plains ?, Mimbres Bosir,
i, Son A-j^iretin Plaint 8, Playos Bosir
4, Jorroco del Muerto Bosir, 9. Worn*I Bosin
5, Tuloroso Bos;n 10, Hochito Bosin
Figure 5.2 Rio Grande drainage basin in New Mexico.
(Anonymous, 1967)
273
-------
1.
2.
3-
J».
5.
6.
7-
8.
9-
10.
11 .
12.
13.
T».
15-
16.
17.
18.
19-
20.
21 .
22.
EXPLANATION
San Luis basin
Espanola basin
Belen-A)buquerque basin
Engle-San riarcial basin
Palomas basin
La Mesa bo)son
Hueco bolsont
Quitman bo 1 son
Mimbres basin
Hachito basin
Wamel basin
North basin
San Augustin Plains basin
Estancia basin
Jornado del Muerto basin
Tulorosa basin
Sa11 bas i n
Upper Pecos region
San Juan bas i n
Delaware-Val Verde basin
Big Bend region
Coastal Plains
Boundary of topographic
subd i v i s ion
Boundory of Rio Gronde drainage
Major areas of igneous rock
outcrop
too*
o . «p . to nowowo met
Figure 5.3 Major topographic subdivisions of Rio Grande Rift,
(Kelly, et al., 1970)
274
-------
[NEW MEXICO"
Jemez
colder a
elen
Bernardo
Magdalenoo
Socorr
NEW MEXICO!. FI Paso
^^^^^••* WMMMMMMMM^**• MMMHi^MMWH^^^ ^» I I VV 9\J
FMEXICO ^ 0
1 i_
/Fault boundary Q
of trough
/ Edge of trough
100 miles
Figure 5.4 "Narrow" interpretation of the Rio Grande Rift
Zone-(Sanford, et al.. 1972)
275
-------
TABLE 5.1 MEAN TEMPERATURE AND PRECIPITATION AT PLACES IN THE RIO GRANDE BASIN,
NEW MEXICO (Anonymous, 1967)
iMfelUr UK
Can*
0*iilM
JMM« •prl«c*
!«••••• M
0*>t« r*
TlWM «B0rtl-
HMta HMintai**
M-JUT -4
U«fluiit hut. I
"iCMU^lUklKt.)
Agricultural [ -
C.ll««. E
It
j
3
^
|
al
^T-
it ^i
0.74
1.79
1.6?
1.04
32,5 .M
.79.
19.2 1.01
24.2 1.02
19.4 .44
.74
27.2 .42
.39
41.0 .40
37.3 .4*
.44
4O,3 .47
'«*"•" —
! 1
1*49
34.3 .99
11.2 Ul*
29.2 1.22
31.2 .33
39.3 .33
44.3 ,43
43.0 ,*7
43.2 .44
_lteSi
f I
41.9 1.06
11*2 1.42
34.0 1.23
39.2 .72
39.1 .42
44.0 .44
32.3 .30
49.7 .24
.63
30.9 .24
r
30.7
37.1
44.0
41.3
46.1
33.3
60.)
3B.7
3*. 3
1
.01
.63
.34
.03
.46
.46
.33
.32
.43
.66
.19
n
31.0 .41
43.2 .78
32.0 .13
36.7 .43
35.3 .30
.53
63.3 .47
69.2 .37
66.7 .77
67.1 .32
! 1
66.2 1.44
33.3 1.21
61.0 .79
66.1 1.13
64.1 .63
.•7
74.» .71
78.1 .73
73.7 .6*
73.9 .37
,? *
70.6 2.36
34.2 2.61
66.6 2.21
70.4 2.26
69.2 1.73
2.21
79.0 1.43
•0.3 1.47
79.2 1.33
2.67
79.4 1.31
£ 1
49.2 3.12
37.4 3.O6
64.9 2.34
68.6 2.21
64.4 2.33
2.33
76.9 1.3*
70.6 1.92
77.3 1.53
2,47
77.7 1.37
1.99
1 I
63.7 2.34
2.09
51.6 1.63
50.2 L.49
62.4 1.19
1.13
1.53
39.6 1.19
2.09
69.9 1.05
1.34
73.0 1.94
70.7 1.44
1.32
71.3 1.14
1.4O
1.93
fi—_
! I
.17
.70
.09
.42
.14
33.9 .40
.34
42.4 .10
47.3 .JO
52.2 .97
1.01
.49
49.3 .47
.04
30.2 .44
.74
43.0 .41
39.3 .41
.97
41.0 .71
.41
•91
>r<*i'
! 1
42.0 .41
19.3 .97
34.7 .43
39.2 .42
34.1 .44
.33
44 .O .42
49.7 .JD
43.9 .24
47.4 ,J1
"
""*"
! i
34.7 .03
11.7 .93
14.9 1.19
31.9 .47
29.3 .44
.30
34.0 .3*
41.7 .41
30.4 .44
41.* .10
— 1_
! i
31.4 |7.*T
•.» M.1I
4i.» M.M
11.W
M.« •.•
39).! 0.?4
• • tf
»»•• T.M
cr\
-------
EXPLANATION
^>—to
Line of equal average annual
precipitation in inches
Line of equal average annual
lake evaporation, in inches
Boundary of Rio Grande drainage
Hajor areas of igneous rock
outcrop
Figure 5.5 Average annual precipitation and lake surface
evaporation. (Kelly, et al., 1970)
277
-------
^:Tjf:rjEV.; ^...aJ7]
x ! J,L. ! \j . 1.&.A-J ;
•«r^"f V "i , ^
n£^3ii
, ^
IM.O.... o.«i...a.
Figure 5 - 6 Normal annual precipitation in New Mexico
(Jetton and Kirby, 1970)
278
-------
|B HUOIOMIM MO MCTIC ZOHC
m CMAOUN zone
B^8 TKANSITKW ZOMC
[!;' J ur«n SOMOKAN
| | LOWCR 9ONOMM
Figure 5.7 Life and crop zones in New Mexico,
(Anonymous, 1967)
279
-------
•reoored ky N. Met. C»lltt* A«r. owl Mtch. Art*. 1957
^ff Irrijattd londi with water teurctt 'from wrfac* water «nly or -from
Mirfae* water tupplementad ky Dumping e-t around water
II I I I Irrigated landl with water Murce antlrely -froai oumaod or artetlan
•round watar
V
Lake* and reeerveirt
Figure 5.8 Vegetative-type map of New Mexico. (Anonymous, 1967)
280
-------
Average annual temperature in rift rises from 4°C (40°F) in the
northern mountains to 16°C (60°F) in the southern valleys.
5.2 GEOTHERMAL CHARACTERISTICS
The Rio Grande Rift has attracted attention as a prospec-
tive geothermal region, primarily because the Union Oil Company
has completed several steam wells in the Valles Caldefa.
In addition to the caldera, other geologic phenomena assoc-
iated with the rift suggest that geothermal resources may be
developed elsewhere within it. These phenomena include:
1) a high heat flow,
2) a distribution of warm and hot ground water,
3) a distribution of late Tertiary volcanic rocks,
4) a thin crust, and
5) a possible magma body near Socorro.
The heat flow ranges from 1.5 to more than 2.5 HFU. Per-
haps even more important, the heat flow is more than 2.0 HFU
over a broad band along the western edge of the rift (Fig. 5.9).
A compilation map (Summers, 1965) showed that thermal water
occurrences are concentrated in the rift.
Late Tertiary rocks, including those of the caldera, occur
throughout the rift. The associated volcanic activity appears
to have begun during Oligocene time and has continued inter-
mittently. Numerous cinder cones mark the landscape. The most
recent events are local basalt flows.
Sanford and his associates at the New Mexico Institute of
Mining and Technology at Socorro have been monitoring micro-
earthquakes for more than a decade. Recent interpretations of
this data suggest that a magma body exists within the rift near
Socorro (Sanford, et al.,1976a and b; Shuleski, et al.,1977).
Gravity studies of Reddy (1966), Bridwell (1976) and
Cordell (1976) suggest that the crust beneath the rift may be
significantly thinner than average. Woodward (1975) has esti-
mated that the crustal extension of the rift near Albuquerque
averages about 0.25 mm/yr (0.01 in/yr). He believes that below
depths of 10.0 to 15.0 km (6.2 to 9.3 mi) the crust is under-
going plastic deformation.
281
-------
109
37°
36°
|rjx;:.l5r2.0HRJ:::
32 °-
109
Figure 5.9 Heat flow in New Mexico. (Reiter, et al.,1974)
282
-------
For geothermal purposes Stone and Mizell (1977) subdivided
the rift (Fig. 5.10) into the following geothermal regions:
1) San Luis Basin,
2) Jemez Mountains,
3) Albuquerque Basin,
4) Socorro-La Jencia Basin,
5) Truth or Consequences-Rincon Basin
6) Southern Jornada del Muerto-Mesilla
Basin and
7) Tularosa Basin.
Detailed discussion of each of these regions is beyond the scope
of this report. Therefore, only major items relevant to geo-
thermal development of each area are mentioned below.
San Luis Basin—
The San Luis Basin is actually the New Mexico portion of a
larger basin by that name that spans the Colorado-New Mexico
border. It consists of a complexly faulted graben located at
the northern extremity of the New Mexico portion of the Rio
Grande Rift in the Rocky Mountains Province (Fig. 5.10). It
covers western Taos County and part of eastern Rio Arriba
County. It is bounded on the east by a major fault system at
the edge of the Sangre de Cristo Mountains and on the west by
the Ojo Caliente Uplift.
Leasing within the San Luis Basin has been confined to
state geothermal resource lands north of Ojo Caliente. No
drilling is known in this area.
Jemez Mountains—
The Jemez Mountains lie within the Rocky Mountains Province
west of the Rio Grande Rift. They cover northern Sandoval
County and most of Los Alamos County. Numerous hot springs
occur within this target area. Four wells have also yielded
thermal waters: the two Los Alamos Scientific Laboratory
(LASL), Fenton Hill or Granite Test wells, the site of the LASL
Dry-hot-rock experiment and two Kaseman oil wells. Valles
Caldera, the remnant of a large volcano which is the dominant
feature of the landscape, is also evidence of intense geothermal
activity in this area about 40,000 years ago.
Leasing and drilling activity in the Jemez Mountains target
area is centered around the Baca Location No. 1 KGRA and the San
Ysidro KGRA. Presently, only state geothermal resource lands
283
-------
Gronta
DATIL-MOOOLLOH
VOLCANIC FIELD
r
MAGDALENA MOUNTAINS
30 mi
Figure 5.10 Subdivisions of the Rio Grande Rift,
(Chapin, 1971)
284
-------
have been leased but Federal lands are available for leasing.
Drilling has been confined to private and fee lands. Union Oil
Company terminated its recent drilling program in 1975; Sun Oil
Company has just begun drilling; Phillips Petroleum Company and
Thermal Power Company both have drilled wells in this region.
Albuquerque Basin—
~The Albuquerque Basin is the largest structural basin
within the Rio Grande Rift. It lies fully within the. Basin and
Range Province covering parts of Valencia and Bernalillo Coun-
ties. Aside from the Quaternary basalt flows capping mesas
along the Rio Grande near Albuquerque, the main evidence of
geothermal activity in this part of the rift has come from three
wells which reportedly yield thermal water.
No Federal or state geothermal resource lands have been
leased in the Albuquerque Basin. Drilling activity is associ-
ated only with private or fee lands.
Socorro-La Jencia Basin—
This area consists of two semiparallel basins separated by
the Socorro-Lemitar-Chupadera Mountains. These basins may
actually be remnants of a larger single basin split by a north-
west trending intrarlift horst (Chapin, 1971). The Socorro-La
Jencia Basin straddles the boundary between the Basin and Range
Province and the Colorado Plateau Province. Woodward, et al.
(1975) would place the western edge of the Basin and Range
Province and the Rio Grande Rift farther west than shown in Fig-
ure 5.10.
Thermal waters discharge at three springs in this area;
infiltration galleries have been constructed at each. Hot water
has also been encountered in a well in Blue Canyon. In addition
to these discharges of thermal water, Tertiary volcanic rocks
occur in the vicinity.
In anticipation of the designation of the Socorro Peak
KGRA, considerable state lands have been leased. No drilling is
known in this target area.
Truth or Consequences-Rincon Basin—
" This area is situated at the western edge of the Basin and
Range Province and includes the portion of the Rip Grande Rift
extending southward from Truth or Consequences in the Engle
Basin, through the eastern part of the Palomas Basin to Rincon
in the central part of the Jornada del Muerto Basin. The area
lies within Sierra County.
Thermal springs in the area include those within the town
of Truth or Consequences (formerly called Hot Springs) and
Derry Warm Springs. Two wells in the area also yield thermal
waters (Summers, 1976).
285
-------
The Truth or Cpnsequences-Rincon Basin has been the focus
of considerable leasing of state geothermal resource lands. No
drilling for geothermal resources is known for this area.
Southern Jornada Del Muerto-Mesilla Basin—
This area lies within the Basin and Range Province and
coincides with the southernmost extension of the Rio Grande
Rift. It also lies within Dona Ana County.
*. *
Thermal waters at Radium Springs are obtained from one
well. Other wells in the area yield thermal waters according to
Summers (1976). The area of the Kilbourne Hole KGRA contains
basalt cinder cones and extensive basalt flows of late Tertiary
age.
Both Federal and state geothermal resource lands have been
leased in the northern part of this area near the Radium Spring
KGRA.
In the southern part of the area, however, in the vicinity
of the Kilbourne Hole KGRA, only Federal lands have been leased
to date. No drilling is known in this area.
Tularosa Basin—
The only occurrence of thermal water in the Tularosa Basin
is at the Carton Well, south of White Sands National Monument.
In addition to this occurrence of thermal water, the young
(about 10,000 years old) and extensive lava flow on the basin
floor near Carrizozo, together with its volcanic source to the
northeast, attest to the considerable geothermal activity here
in very recent geologic time.
5.3 GEOLOGY
The Rio Grande flows through a structurally and physio-
graphically low valley that constitutes the Rio Grande Depres-
sion. A major continental rift, the depression extends south-
ward over 645 km (400 mi) from southern Colorado, through the
length of New Mexico, to near El Paso, Texas (Kelley, 1952).
The rift contains the highest mountains and deepest intramontane
basins of the territory it traverses. Altitudes in the Rio
Grande Rift range from 1,100 m (3,600 ft) in the El Paso Valley
to 4,010 m (13,160 ft) on top of Mount Wheeler. Altitudes along
the floor of the Rio Grande Valley range from 1,100 m (3,600 ft)
in El Paso Valley at the Texas state line to 2,270 m (7,440 ft)
in San Luis Valley at the Colorado state line.
In New Mexico, four geological provinces with very dif-
ferent characteristics exist in juxtaposition with the Rio
Grande Rift. The northern part of the rift bisects the high
ranges of the southern Rocky Mountains and has intermittent
286
-------
contact with the Colorado Plateau to the west. The southern
part of the rift is bordered on the west by the Colorado Plateau
and the Basin and Range Province. The Great Plains lie to the
east of the mountains bordering the rift (Kelley, 1954).
Plate 5.1 shows the surface geology of the Rio Grande Rift
area. Countless faults criss-cross the area,and ages of exposed
rocks range from Precambrian to Recent. Exposures in ^the north-
ern mountains show Mississippian and Pennsylvanian Sedimentary
strata overlying the Precambrian rocks. A few rocks of ques-
tionable Devonian age crop out in the Sangre de Cristo Mountains,
but no older Paleozoic rocks have been found. In the south,
Cambrian, Ordovician, Silurian, Devonian and Mississippian
strata all crop out between the Precambrian and Pennsylvanian.
Table 5.2 gives a generalized stratigraphic section.
Faulting in the Rio Grande Rift is discontinuous. No
single huge fault bounds the Rio Grande Rift on either side.
Instead, a series of subparallel faults combine to create linear
features that we may regard as bounding the rift area. An
individual fault may be traced for miles along its strike until
the throw diminishes and that fault dies out. Nearby faults in
the system take up the movement and the overriding pattern of
blocks and troughs continues even though individual faults do
not.
Normal faults commonly bound rift zones, but thrusts and
high-angle reverse faults form the apparent limits of some parts
of the Rio Grande Rift area. Most of the reverse faults occur
along the northeastern rift boundary in the Sangre de Cristo
Mountains.
With discontinuous faulting in both uplifted and down-
dropped parts of the rift system, some areas can be interpreted
as horsts within a broad structural trough or as uplifted blocks
along the rift boundary. Similarly, some structural depressions
may be treated as separate grabens flanking the main rift
graben, or as parts of the main rift graben which lie beside
horsts in that depression.
The complex structure and wide range of geologic formations
found in the Rio Grande Rift prevent any simple, brief charac-
terization of the area from being universally accurate.
The uplifted blocks expose Precambrian rocks in several
places. Cambrian to early Miocene sedimentary strata lie above
the Precambrian rocks. Tertiary and Quaternary volcanics (not-
ably in the Jemez Mountains), intrusive rocks of various ages
(mostly Late Cretaceous and Cenozoic) and alluvial deposits
round out the geologic assemblage in the uplifted blocks. Steep
reverse faults, normal faults and folds complicate the struc-
tural picture. In general, the northern ends of uplifted blocks
287
-------
TABLE 5.2 GENERALIZED STRATIGRAPHIC SECTION IN THE RIO
GRANDE BASIN, NEW MEXICO (Anonymous, 1967)
(•Known or probable •quLfeir. r*9*rdl**« of araal extant or production potential.
Svateei
Quaternary
Quaternary
•nd
Tertiary
Quaternary! T)
e*d
Tertiary
Tertiary
Cretaceova
JuraaalC
Trleaelc
Feral or
Fenian and
Pannaylva-
nlan
.la*
DevefllW
Cawferlw
Frecavkrlan
StrattgrtpMt
•AllwTllM
race, and b» Ja-
la depeeUi
•Volcanic
oeMOlai
•Santa F*
Croup
Cellaceo fore*-
Sodlaemtary
rochi
*0}o AlMO
Sandelone
Ilrtlmnd Shale
and Fruit l«nd
POTMilon
*Hctured
Cllffa
SaJidptone
Lewi. Shale
Croup
Shalt
"Dakota
Sv.ii.tan
•Horrlwn
Formation
•Bluff
Sandetone
•uaaMrvllla
formation
Twill to
LlMBtone
*tntred*
$anda tone
•Chlnli
PDraaLtlon
*San Andrea
•Clorlex*
Sandstone
•YeeO
rotation
*abo
"Braetlon
**an|re do
Crlato
Formation
*Naajdalena
CtouB
Lake V.ll.y
Liawatone
Itrcba
•bel.
ruBMlawn
Dolomite
DolaaUte
11 F.BO
LlaHBtona
ill., Fere»-
tlen
**•(» orphic
and Ifneoua
ncia
ThlCBJiee*
(EMI)
Canerally
thtni leei
cban 100
auch ea
JOO
0 to I. ttO*
0 to 4,000*
HO to
i.JOO
0 to
6,000+
70 to 100
100. to
600*
33 to 73
400 to
1.400
2,500*
2,500
35 co 2*5
210 to 910
75 to ISO
H to 120
0 to IOT
ISO to 250
600 Co
1,600
X to 1,OOO
70 co 300
200 to
1,100
300 to
1,100
230 to
i.too
0 to
1.300
0 to 60
3D to tOS
!*•• than
30 to
•hout 90
43O*
ISO co
4 SO*
Dl it r I but Ion
hronnlal atroa* channel!,
flood fUlni, and Locally
In dry arrayoi.
to witolni. T«rr»e*a ar*
orwlnint ilonf tta Unta
Fa llvff.
C»»* *any aaui and occuri
MdlMntary roeki in •cit
of tba Rio Grand* bmiin.
Fill! th« Rio Grand* trvufh.
aga la SanCi Fa County; prob-
araa it it««t dtoth.
SodtaMitmry rock* ara priaant
throughout th» Ho Grand* baain',
howavar. aboniU-'t MMvicUtur*
hart.
San Juan litructural) haaln.
do.
do.
do.
!!•• WBC of the Rl* Grande
baain at ar.at dapth.
(atructural) baain and under-
lie* avit of the Rio Crvdc
San Juar (atruttural) b»«ln
and oeat of tie Crinda baain.
San Ju*n (•tructural)
Wain; m*y luiderll* other
p*rta of the Ho Crajidc
baain, but probably at
.treat dapth.
5*n Ju*r UtructuraL)
b*»ln| thla foramtlon oc Ita
•qulvftlant my underlie ochar
•erta at the Rio Grande b.iln.
do.
do.
do.
do.
Frobcbly widaeprood and crop*
out In or undarll« acat of
Klo Grand* baeln.
aan Juan (atructural) baain.
Thli Corawtlon or It* aqulva-
lant aey underlie other parti
of tbe lio Gr*nd« baain.
Uldeapraadl crop* aut In or
un4orllai Mat of Klo Grande
baaln.
do.
fanfri da Crlato tewitaln.;
•ay unoarlla Santa Pa
Vldeapreedi cropa out In or
woorllee aoat of the baeln.
Mauntalne In aowthan part of
tho haain.
do.
d*.
do.
Underlie all of tbe Uo
Crande baa In.
Fhyaieal ar«MrUn
Unconaolldatad allc. tanit.
and fra««l.
•tit, aand, graval , and
•out dart. Cravat and
bout da r devoalta a*y ba
lenticular.
laaalt, •ndealte. rkyolUa,
Clay, illi, aand. and
unconaolldattd. Conial na
ahalat alac My cortaln
eoew congiMMrete.
Sar-deton*. a.lltitofia, ahala.
CoarM 'grained, eon|Ioe»ratfc
•endaton*.
Sbale. aondy ahale, alltacone
and Interbodded aandacone.
Thin- to thick-bedded Band-
atone with lnt«rb*dd*d ellt-
etone and ahale.
bedded alltitone, aandatone,
and Ua.iton*.
atone and coal.
•ton* interbadded naar the baa*
locally.
Sandatonr with Interbedded
carbonecvoui ahalr.
V«Tlecated ahale, clayatonc,
and •llt*ton« with Intar-
bedded avdetonc.
Senditon«.
Sendacone, ellteton*, end
•andy ahale.
Gysaua and Claalle llatt-
atone.
Croaa-bedded aand it one.
Hudacona and il Intone with
incerbedded avditona.
LlMaatone, aandatone,
elltetonc, and §ypii4».
Thick- bcddod to Maalve
aandatone.
Slltttone, Bwdatone, and
ahala.
arkoilc undatone, allc-
atona, end ahale.
Arhoalc ehala, aandatona,
and eong loaNrata .
LlBMBtone, Mndatone, and
interbaddad ehala.
LlMBton* and eoaM ehale.
•hale, elayetone, and eoew
aendatone and alltaton*.
Cbarty doloadte
Haaalva doloadte, chert Ua»-
etona, claTatone. and a baaal
aandetena.
Thin-bedded llaaatona) baaal
unit la laadnated, chart y
Ueatetone.
Thin- co talek.beaded aand-
atone wich aoeai een«lomcat.
and llwatont.
Cranlta, achlat, ptelaa, and
other BBptiBBtritilc ncka.
watir-baarini eKera
to well*.
on fracture pereaiablllty and ^aturated
or reljjible aaulfer.
Ytelda lar»* quantliUi of vattr I aa
Thta la th* aoac aitt-alve » d rtllibj
Sewta Fc.FonMUO'- tlva at |r«ai depth
eleewnare 1". the boaln and uneconomical
to t«o.
Contrail y yl*'d aaal< quar>iltl*» of
H«t«r to wile; locally, boda of aand-
atona might yield andaratB quantltlaai
•rd cuawlatlve yield frae. eeu>y bad* of
aandatone could be lane.
Known to yield 2 to 30 |pau
lada of aandatonc of low paraeabtllty
might ylald aawll quantity of vatcr.
Genera I Li not considered aa an aquifer.
Low poroalty and low permeability.
Generally noc conaldered aa an aquifer;
however, a*y yield aawll quanclUea of
Mter locally.
bed! of land it on* In lover part Bight
yield aw 11 awmnt at water, but It prob-
ably la laUna.
quantltla* of wateri not tapped lr eonv
areaa became of great depth.
quancltlea of water.
Ylelda anall to Moderate qu«ntltlaa of
water to welli; not tapped at «er>
quality orobablv beat near outcrooa.
Ylelda aawll to aod«r,te quantltlei of
water to walla; depend i on Mturaicc)
thlckneaa of aandatone.
Hay yield ***LL quantltlea of Macer to
well* where aatureted. Generally hat
low perMeblllty.
Not known to yield water t? walla.
Yictda very little vater to wclla.
Hater generally baa hl|h aulfate con-
tent.
nay yield eaaUl ouantltlai of poor
aualtty water to wella.
Sanditone a«y ylald aaaill to Moderate
quantities of (eneratly poor quality
water; quality la boat cloae to the
out c rose,
Fracture or eolutfon-cbann*! peneabll-
Ity. Hay yield larj» quantldea of
vater to wolle. C Ylelda aa eucb aa
3,000 ipai near Cranta.) Hater quality
la variable and la b*at cloae to the
outcrooa.
tUy ylald avderate quantltlec. of water
EO valla.
of vater ta valla.
Generally low penaaabllity. but yield
of water Co walla My range fnm avail
to lane.
Generally not «i aquifer In the baaln
bee HIM depth to water la too great.
Hay yield avail quantltlea of water to
wella.
Unknown.
DC
Do.
Do.
Do.
Do.
Yield aawll quantltlea of water to
walla, generally new the outcrope.
288
-------
are structurally higher, exposing rocks older than those in
their southern parts.
Downdropped troughs contain thick sedimentary deposits
usually assigned to the Santa Fe Group with an age of Miocene to
Recent. Several areas of Miocene and younger volcanics follow
the rift. The great thickness of combined Tertiary and Quater-
nary sediments and volcanics masks older structures in the
basins.
Exposed faults in the Santa Fe Group show dips of 70° to
90°. These high angles may not represent the faults at depth
since faults cutting the Santa Fe Group are young and the dips
probably are measured close to the original surface. They may
therefore represent fault refraction near the surface. Most
faults in the Rio Grande Valley have a northward trend; those
trending eastward tend to be shorter and more widely spaced.
5.4 HYDROLOGY
The Rio Grande Rift includes several drainage basins (Figs.
5.1 and 5.2) which are not always defined in the same way.
Both surface water and ground water are ultimately derived
from precipitation. Most water evaporates; plants transpire
some of it; and some water runs off so rapidly that it erodes
the land and picks up suspended and dissolved solids that make
it unfit for most desired uses. A small portion, perhaps as
much as 10% in the mountains, infiltrates to become ground water
recharge.
The actual amount of water consumed by evaporation (Table
5.3) and transpiration depends on several factors, including
temperature, relative humidity of the surrounding air and
velocity at which the air passes, and density and type of vege-
tation. The division of water between surface flow and ground
water is affected by these variables and also by other factors
such as rate of precipitation and porosity and slope of the
surface on which precipitation falls. Gentle rains infiltrate
more completely than cloudbursts delivering the same volume of
water, irrespective of the vegetation they fall on.
All these factors interact to determine actual water sup-
plies available for use, with no single factor completely over-
riding the others. For instance, a desert assemblage of brush,
sparse grass and cactus transpires less water than the trees,
brush and thick grass of mountain forests, but the forest assem-
blage covers the ground more completely and thereby increases
infiltration. The forest vegetation also reduces erosion and
thereby reduces sediment load in streams.
289
-------
TABLE 5.3 AVERAGE CLASS A LAND PAN EVAPORATION IN INCHES, RIO GRANDE BASIN IN NEW MEXICO
MEXICO (Anonyipou s, 1967)
to
vo
o
Station
Bosque del Apache
(1947-62)
Cabal lo Dan
(1942-62)
El Vado
(1936-62)
Elephant Butt* Dam
(1934-62)
Jemez Dam
(1954-62)
Narrows
(1947-62)
Santa Fe
(1948-62)
State University
(1918-62)
Jan*
3.21
3.65
1.84*
3.49
2.96*
2.99
2.25*
2.94
Feb.
4.42
5.42
1.85*
5.30
2.97*
4.68
2.26*
4.39
Mar.
8.18
9.34
3.69*
8.95
5.93*
7.72
4.51*
7.61
Apr.
10.49
12.34
5.74
12.58
9.76
11.09
8.17
10.01
May
12.80
15.28
7.78
15.80
12.70
13.67
9.62
12.20
June j
13.79
16.80
9.73
17.41
14.98
15.26
10.94
13.20
July
12.08
13.96
8.97
14.75
13.97
13.59
10.29
11.96
Aug.
11.02
12.29
7.55
12.94
12.10
11.81
8.79
10.33
Sept.
8.66
10.36
6.3?
10.66
10.34
10.18
7.90
8.37
Oct.
6.40
7.56
4.57
8.17
7.12
7.52
5.47
6.10
Nov.
3.80
4.83
2.20
"5.13
4.03
4.36
3.48
3.78
Dec.
2.74
3.22
1.23*
3.42
1.98«
.2.84
1.50*
2.64
Annual
97.61
115.05
61.54*
118.60
98.84'
105.71
75.1*
93.53
* Calculated by percentage distribution.
-------
Water in New Mexico has long been regarded as a public
resource that may be appropriated for beneficial use by a pri-
vate party. This appropriation doctrine contrasts the theory
that possession of land carries with it the right to water
occurring on or under that land. It protects early water users
from ruin by latecomers whose developments interfere with estab-
lished use. This doctrine serves well in arid environments
where water often limits development, and security in water
supply is therefore a requisite part of any project. *
The State Engineer exercises jurisdiction over appropri-
ation and use of surface water in New Mexico and has similar
control over ground water in underground basins that he "de-
clares" by determining and publishing the boundaries of said
basins. Most water in the rift also is directly or indirectly
affected by interstate and international agreements with
Colorado, Texas and Mexico concerning the flow of the Rio
Grande System.
Use of surface water in the Rio Grande Rift of New Mexico
predates all known records. Indians were irrigating crop land
when the Spanish arrived and ruins of even earlier irrigation
projects can be found. Surface waters are still diverted and
impounded for irrigation and other uses ranging from industry to
recreation. Figures 5.11 and 5.12 show surface water measurements
for some stations in the rift.
Gaging stations on the Rio Grande record stream flow at
several places,but the stream flow they record is not identical
with the runoff resulting from precipitation. Reservoirs con-
trol their discharge flows, irrigation works remove water from
the river at several places, the return flow from irrigation
water seldom can be measured, and ground water enters the river
in unmeasured amounts. Still, the discharge measured at gaging
stations provides the basic data on which surface water appor-
tionments are based.
Various people and government agencies have divided the Rio
Grande drainage basin into streams. These sections do not
provide for a unit called the Rio Grande Rift in New Mexico.
The major distinction between the Upper Basin and Lower
Basin of the Rio Grande follows from the character of the river
itself. From its headwaters in Colorado to Fort Quitman, Texas,
the Rio Grande flows rapidly downhill along the major rift
valley in a series of constrictions and irrigable valleys.
Below Fort Quitman the river leaves the main rift valley and
meanders slowly southeast down a gentle grade to the Gulf of
Mexico. The Rio Grande runs 3,060 km (1,900 mi) from its head-
waters to the Gulf of Mexico of which 1,050 km (650 mi) lie in
the Upper Basin. The Upper Basin includes all the drainage area
above Fort Quitman and contains 82,970 sq km (32,035 sq mi).
I
291
-------
... STBTE LINE
COUNTY LHC
'— DRAINAGE BASIN BOUNDARY
A USGS GAGING STATION
$ STATE CAPITAL
• COUNTY SCAT
O OTHER TOWNS
Figure 5.11 Average monthly and annual discharges at selected
gaging stations, Rio Grande Valley and area of
direct surface runoff. (Anonymous, 1967)
292
-------
• M j'iJ-A L e o j ,_ [_
Mtor dltchorgt Of flrtomi,
In cubic ft«t ptr itcond.
(Mognitud* of ditchorgt
r«pr»»«nf»d by nldth of
tin*. Sot icolt.)
Lin* olong which tquol
runoff occurs, in inchtt
Figure 5.12 Mean discharge of principal streams, in cubic feet
per second, and annual runoff, in inches, in New
Mexico, for periods of record. (Anonymous, 1967)
293
-------
The Upper Basin of the Rio Grande is further divided into
the San Luis Section, the Middle Section, and the San Marcial-
Fort Quitman Section. These sections of the Upper Basin hold
importance in the division of surface water among the states of
Colorado, New Mexico and Texas as prescribed by the Rio Grande
Compact.
The San Luis Section includes the Rio Grande drainage in
Colorado, which contains 19,900 sq km (7,700 sq mix above the
gaging station at Lobatos, Colorado. The gaging station at
Lobatos Bridge measures Colorado's delivery of water to New
Mexico under the Rio Grande Compact. The 68-year mean discharge
through 1967 was 54,350 ha-m (440,650 acre-ft). Table 5.4 shows
discharge data for the Rio Grande at Lobatos.
The Middle Section of the Upper Basin of the Rio Grande
includes the river and its tributary valleys from the Colorado-
New Mexico border to the San Marcial gaging station at the head
of Elephant Butte Reservoir, a river distance of 435 km (270 mi)
that contains about 52,000 sq km (20,000 sq mi) of drainage
basin. This area contributes most of the water supply to the
Rio Grande that originates in New Mexico.
In the language of the Rio Grande Compact, the Rio Grande
below San Marcial runs in Texas, and New Mexico's water delivery
is measured at the gaging station at San Marcial. That delivery
shows a 72-year mean discharge of 114,910 ha-m (931,590 acre-ft)
through 1967. Table 5.5 gives discharge data from the San
Marcial gaging station. Across the Middle Section of the Upper
Basin of the Rio Grande, gaging stations show an increase of
5,540 ha-m (44,940 acre-ft) in average annual discharge.
The San Marcial-Fort Quitman section of the Upper Basin of
the Rio Grande contains 400 km (250 mi) of river between San
Marcial, New Mexico, and Fort Quitman, Texas, and about 11,140
sq km (4,300 sq mi) of drainage area. Two major storage facili-
ties of the Rio Grande System, Elephant Butte and Caballo reser-
voirs, lie in this southern reach. The Rio Grande discharges
19,180 ha-m (155,490 acre-ft) at Fort Quitman, according to a 46-
year average through 1968 (Table 5.6).
Irrigated acreage varies widely through the years from an
estimated 10,342 ha (25,555 acres) in about 1600 to an estimated
103,780 ha (256,445 acres) in 1964. Of the 103,780 ha irrigated
in 1964, about 53,657 ha (132,590 acres) relied on surface water,
8,630 ha (21,325 acres) used groundwater and the other 41,492 ha
(102,530 acres) used a combination of surface and groundwater.
Surface water in the Rio Grande above Elephant Butte Reser-
voir has been fully appropriated. Therefore, any new use of
surface water would force the abandonment of a previous use.
294
-------
TABLE 5.4
ANNUAL DISCHARGE OF THE RIO GRANDE NEAR LOBATOS,
COLORADO (Jetton and Kijrby, 1970)
Calendar
year
-
(1)
1900
01
02
03
OU
05
06
07
08
09
1910
11
12
13
11*
15
16
17
18
19
1920
21
22
23
21*
25
26
27
28
29
1930
31
32
33
~f~t
31*
35
•J S
36
37
38
39
Annual
discharge
in
acre-feet
(2)
301*, ooo
281*, 000
98,700
627,000
188,000
986,000
851*, ooo
1,1*1*0,000
362,000
933,000
556,000
1,01*0,000
81*9,000
295,000
595,000
1*71,000
769,000
799,000
260,000
612,000
1,01*0,000
863,000
671*, ooo
696,000
753,000
323,000
1*26,000
72U,000
325,000
598,000
270,000
126,000
596,000
237,000
•" M/ i y ^ —••»*•
98,880
360,1*00
^J^s-+r J • *r v
281,000
1*65,800
570,900
207,700
Five-year
moving
average
in
acre -feet
(3)
-
-
-
-
300,31*0
1*36,7UO
550,71*0
819,000
766,000
915,000
829,000
866,200
71*8,000
73l*, 600
667,000
650,000
595,800
585,800
578,800
582,200
696,000
711*, 800
689,800
777,000
805,200
661,800
571*, 1*00
58U, 1*00
510,200
1*79,200
1*68,600
1*08,600
383,000
365,1*00
265,580
283,660
3lU,66o
288,620
355,1*00
377,160
Ten-year
moving
average
in
acre -feet
00
^
-.
-.
-
—
—
-.
—
—
607,670
632,870
708,1*70
783,500
750,300
791,000
739,500
731,000
666,900
656,700
621*, 600
673,000
655,300
637,800
677,900
693,700
678,900
6l*U, 600
637,100
61*3,600
61*2,200
565,200
1+91,500
1*83,700
1*37,800
372,390
376,130
361,630
335,810
360,1*00
321,370
Departure
from
mean in
acre-feet
(5)
-136,651*
-156,651*
-31*1,95!*
+186,31*6
-252,65U
+51*5,3^6
+1*13,31*6
+999,31*6
- 78,651*
+1*92, 3!*6
+115,3!*6
+599,31*6
+1*08,31*6
-11*5,65!*
+15!*, 31*6
+ 30,3!*6
+328,31*6
+358,3!*6
-180,65!*
+171,^31*6
+599, 3U6
+1*22,31*6
+233,31*6
+255,31*6
+312,31*6
-117,651*
- 1U.65U
+283,31*6
-115,651*
+157,31*6
-170,651*
-311*, 651*
+155,346
-203,65!*
-3l*l,77l*
- 80,25!*
-159,651*
+ 25,11*6
+130,21*6
-232,951*
Accumulative
departure
J'rom mean
. *. in
acre- feet
(6)
- 136,651*
- 293,308
- 635,262
- 1*1*8,916
- 701,570
- 156,22^
+ 257,122
+1,256,1*68
+1,177,811*
+1,670,160
+1,785,506
+2, 38U, 852
+2,793,198
+2,61*7,51*1*
+2,801,890
+2,832,236
+3,160,582
+3,518,928
+3,338,27!*
+3,509,620
+1*, 108, 966
+1*, 531, 312
+1*, 76!*, 658
+5,020,001*
+5,332,350
+5, 211*, 696
+5,200,01*2
+5,1*83,388
+5,367,73!*
+5,525,080
+5,35^,1*26
+5,039,772
+5,195,118
+1*, 991, l*6U
+1+, 61*9, 690
+U, 569, 1*36
+1*, 1*09, 782
+1*, 1*3!*, 928
+1*, 565,17U
+1*, 332, 220
295
-------
TABLE 5.4
Calendar
year
(1)
191*0
1*1
1*2
1*3
1*1*
1*5
1*6
1*7
1*8
±9
1950
51
52
53
5!*
55
56
57
58
59
I960
61
62
63
6U
65
66
67
Annual
discharge
in
acre-feet
(2)
105,700
95^,300
681,800
183,500
606,300
276,800
115,100
230,300
661*, 200
572,600
132,100
7l*, 320
1*68,1*00
122,100
59,570
63,120
70,130
l*l*U, 900
362,500
88,1*20
201,000
169,200
315,300
72,570
57,1*1*0
1*98,600
255,1*00
160,1*00
Five-year
moving
average
in
•cre-feet
(3)
326,220
1*60,880
50^,080
U26.600
506,320
5^0,5^0
372,700
282, UOO
378,5^0
371,800
3^2,860
33^,700
382,320
273,900
171,300
157,500
156,660
151,960
200, QUO
205,810
233,390
253,200
227,280
169,300
163,100
222,620
239,860
208,880
Ten-year
moving
average
in
acre- feet
00
30U,9^0
387,770
396,350
391,000
UUl,7Uo
1*33,380
1*16,790
393,21*0
1*02,570
1*39,060
1*1*1,700
353,700
332,360
326,220
271,550
250,180
21*5,680
267,lUo
236,970
188,560
195A50
201*, 930
189,620
181*, 670
18U, 1*60
228,010
21*6,530
218,080
Departure
from
mean in
acre -feet
(5)
-33^,95^
+513,61*6
+2l*l,ll*6
-257,15^
+165,61*6
-163,851*
-325,55^
-210, 35^
+223,5^6
+131,9^6
-308,55^
-366,33^
+ 27,71*6
-318,55!*
-381,081*
-377,53!*
-370,521*
+ It, 2H6
- 78,153
-352,231
-239,651
-271,1*51
-125,351
-368,081
-383,211
+ 57,9^9
-185,251*
-280,25!*
Accumulative
departure
from mean
in
acre-feet
(6)
+3,997,266
+1*, 510, 912
+1*, 752, 058
+1*, 1*9!*, 901*
+U, 660, 550
+1*, 1*96, 696
+1*, 171,ll*2
+3,960,788
+1*, 181*, 33!*
+1*, 316, 280
+1*, 007, 726
+3,61*1,392
+3,669,138
+3,350,581*
+2,969,500
+2,591,966
+2,221,1*1*2
+2,225,688
+2,11*7,535
+1,795,301*
+1,555,653
+1,281*, 202
+1,158,851
+ 790,770
+ 1*07,559
+ 1*65,508
+ 280,25!*
0
68 year mean dischargeJ 1*1*0,650 acre-feet.
296
-------
TABLE 5-5
ANNUAL DISCHARGE OF THE RIO GRANDE AT SAN MARCIAL
NEW MEXICO (Jetton and Kirby, 1970)
Calendar
year
(1)
1896
97
98
99
1900
01
02
03
OU
05
06
07
08
09
1910
11
12
13
11+
15
16
17
18
19
1920
21
22
23
21+
25
26
27
28
29
1030
31
32
^^-
33
~s J
Ojj,
^5
Jx
36
.J^
37
~t (
38
39
Annual
discharge
in
acre-feet
(^
581,500
1,781,000
865,100
239,500
1+67,900
656,200
200,700
1,309,000
65!*, 200
2,1+22,000
1, 561*, 000
2,158,000
771* , 100
1,280,000
852,700
1,800,000
1,500,000
525,1*00
1,178,000
1,373,000
1,61*9,000
1,050,000
1*11,200
1,579,000
1,91*3,000
1,1*88,000
938,1*00
l,22l*,000
1,1*10,000
1*19,000
1,050,000
1,350,000
591,000
1,1*60,000
731,000
1*90,000
1,1*00,000
716,100
2l*l*,UOO
1,028,000
866,900
1,558,000
1,051*, ooo
52l*,l*00
Five-year
moving
average
in
acre- feet
(3)
_
_
—
—
787,000
801,91*0
1*85,880
57**,660
657,600
1,01+8,1*20
1,229,980
1,621,1*1+0
1,51**, 1*60
1,639,620
1,325,760
1,372,960
1,21+1,360
1,191,620
1,171,220
1,275,280
1,21*5,080
1,155,080
1,132,21+0
1,212,1*1+0
1,326,1*1*0
l,29l+,2l+0
1,271,920
l,l+3l+, 1+80
1,1*00,680
1,095,880
1,008,280
1,090,600
96U, 000
971*, ooo
1,036,1*00
921*, Uoo
931*, 1*00
959,1*20
716,300
775,700
851,080
882,680
950,260
1,006,260
Ten -year
moving
average
in
acre-feet
oo
_
_
—
_
—
_
, _
_
_
917,710
1,015,960
1,053,660
1,01*1*, 560
1,11*8,610
1,187,090
1,301,1*70
1,1*31,1*00
1,353,01*0
1,1*05,U20
1,300,520
1,309,020
1,198,220
1,161,930
1,191,830
1,300,860
1,269,660
1,213,500
1,283,360
1,306,560
1,211,160
1,151,260
1,181,260
l,i99,2>*o
1,187, 3^0
l,o66.lUo
966,3^0
1,012,500
Q6l,710
81*5,150
906,050
887,71*0
908,5^*0
95!*, 81*0
861,280
Departure
from
mean in
acre-feet -
(5)
- 350,090
+ 81+9,1+10
66,1+90
- 692,090
- 1+63,690
- 275,390
- 730,890
+ 377,1+10
- 277,390
+1,1+90,1+10
+ (32,1+10
+l,?26,UlO
- 157,^90
+ 31*8,1+10
- V8,890
+ 868,1+10
+ 568,1+10
- i+06,190
+ 21*6, UlO
+ 1+1+1,1+10
+ 717,1+10
+ 118,1*10
- 520,390
+ 61*7,1*10
+1,011,1*10
+ 556,1*10
+ 6,810
+ 292,1*10
+ 1*78,1*10
- 512,590
+ 118,1*10
+ 1*18, UlO
- 3^0,590
+ 528,1*10
- 200,590
- 1*1*1,590
+ 1*68,1*10
- 215,1*90
- 687,190
+ 96,1*10
- 6U.690
+ 626,1*10
+ 122,1*10
- 1*07,190
Accumulative
departure
- from mean
*• in
acre-feet
(6)
- 350,090
+ 1*99,320
+ 1*32,830
- 259,260
- 722,950
- 998,3^0
-1,729,230
-1,351,820
-1,629,210
- 138,800
+ 1*93,610
+1,720,020
+1,562,530
+1,910,9^0
+1,832,050
+2,700,1*60
+3,268,870
+2,862,680
+3,109,090
+3,550,500
+1*, 267, 910
+1*, 386, 320
+3,865,930
+1*, 513, 3^0
+5, 52U, 750
+6,081,160
+6,087,970
+6,380,380
+6,858,790
+6,31*6,200
+6, 1*61*, 610
+6,883,020
+6,51*2,1+30
+7,070,81+0
+6,870,250
+6,1*28,660
+6,897,070
+6,681,580
+5,99^,390
+6,090,800
+6,026,110
+6,652,520
+6, 77U, 930
+6,367,71*0
297
-------
TABLE 5.5 (continued)
Calendar
year
(1)
19^0
Ui
1*2
1*3
1*1*
U5
1+6
1*7
1+8
1*9
1950
51
52
53
5^
55
56
57
58
59
1060
61
62
63
6U
65
66
67
Annual
discharge
in
acre-feet
(2)
369,000
2,831,000
1,9^0,000
1+18,200
l,02l+,000
8ii*,Uoo
289,300
1*33,700
933,500
1,051*, 000
307,000
111*, 100
1,003,000
260,500
215,600
26U.200
136,300
1,21*0,000
1,292,000
2l+7,500
551,600
5M*,500
71*5,900
267,000
169,000
1,036,000
568,800
61*6,700
Five-year
moving
average
in
acre-feet
(3)
8?!*, 1+60
l,2tv, ,280
1,3^3,680
1,216,520
1,316,^0
1,U05,520
897,180
595,920
698,980
70U,980
603,500
568>60
682,320
5^7,720
380, oUo
371,^80
375,920
U23,320
629,620
636,000
693,1*80
775,120
676,300
1*71,300
1*55,600
552,1*80
557,3^0
537,500
Ten-year
moving
average
in
acre-feet
CO
825,080
1,059,180
1,113,180
1,083,390
1,161,350
1,139,990
1,082,230
969,800
957,750
1,010,710
1,001*, 510
732,820
639,120
623,350
5U2,510
1*87,1*90
1*72,190
552,820
588,670
508,020
532,1*80
575,520
5^9, 810
550,1*60
51*5,800
622,980
666,230
606,900
Departure
from
mean in
acre-feet
(5)
- 562,590
+1,899, Mo
+1,008,1*10
- 513,390
+ 92,UlO
- 117,190
- 61*2,290
- 1*97,890
+ 1,910
+ 122,1*10
- 62U,590
- 817,1*90
+ 71,1*10
- 671,090
- 715,990
- 667,390
- 7%, 290
+ 308,1*10
+ 360,1*10
- 681*, 090
- 379,990
- 387,090
- 185,690
- 66**, 590
- 762,590
+ 10U,1*10
- 362,790
- 28U, 890
Accumulative
departure
from mean
in
acre-feet
(6)
+5,805,150
+7, 70U ,560
+8,712,970
+8,199,580
+8,291,990
+8, 17U, 800
+7,532,510
+7, 03!*, 620
+7,036,530
+7,158,91+0
+6,53^,350
+5,716,860
+5,788,270
+5,117,180
+1*, 1*01, 190
+3,733,800
+2,938,510
+3,21*6,920
+3,607,330
+2,923,21*0
+2,51*3,250
+2,156,160
+1,970,1*70
+1,305,880
+ 5U3,290
+ 61*7,680
+ 281*, 910
+ 0
72 year mean:931,590
298
-------
TABLE 5.6
ANNUAL DISCHARGE OF THE RIO GRANDE AT FORT QUITMAN ,
TEXAS (Jetton and Kirby, 1970)
Calendar
year
(1)
1923
24
25
26
27
28
29
1930
31
32
33
34
35
36
37
38
39
1Q40
41
42
1+3
44
45
46
47
1+8
1+9
1950
51
52
53
*/ J
54
55
s s
56
x*-'
57
58
59
Annual
discharge
in
acre- feet
(2)
332,1+00
373,800
267,880
276,250
240,920
263,810
211,780
188,030
211,650
211,120
213,790
102,420
145,380
149,590
178,290
276,240
152,180
124,320
330,490
1,270,400
233,290
272,900
207,710
131,380
90,780
75 , 340
131+, 030
123,530
25,690
11,129
20,329
*•• v y -^ x
14,886
5,888
X J w w
6,010
4,843
36,152
13,226
Five-year
moving
average
in
acre-feet
(3)
_
—
—
_
298,250
284,530
252,130
236,160
223,240
217,280
207,270
185,400
176,870
164 , 460
157,890
170 , 380
180 , 340
176,120
212 , 300
1+30,730
422 \ 140
446^280
462,960
423,140
187,210
155,620
127,850
111,010
89,870
73,91+0
62,Q40
39,110
15 , 580
^ jf 7 jf
11,650
10,390
13,560
13,220
Ten-year
moving
average
in
acre-feet
(1+)
—
_
—
_
_
_
—
_
_
257,760
245,900
218,760
206,520
193,850
187,590
188,830
182,870
176,500
188,380
294 , 310
296,260
313,310
319,540
317,720
308,970
288,880
287,060
286,980
256,500
130,580
109,280
83,480
63,300
50,760
42,170
38,250
26,170
Departure
from
mean in
acre -feet
(5)
+ 176,910
+ 218,310
+ 112,390
+ 120,760
+ 85,430
+ 108,320
+ 56,290
+ 32,540
+ 56,160
+ 55,630
+ 58,300
- 53,070
10,110
5,900
+ 22 , 800
+ 120,750
3,310
31,170
+ 175,000
+1,114,910
+ 77,800
+ 117,410
+ 52,220
24 , 110
- 64,710
80,150
- 21,460
- 31,960
- 129,800
- 144,360
- 135,160
- 140,600
- 149,600
- 149,480
- 150,650
- 119,340
- 142,260
Accumulative
departure
from mean
in
acre- feet
(6)
+ 176,910
+ 395,220
+ 507,610
+ 628,370
+ 713,800
+ 822,120
+ 878,410
+ 910,950
+ 967,110
+1,022,740
+1,081,01+0
+1,027,970
+1,017,860
+1,011,960
+1,034,760
+1,155,510
+1,152,200
+1,121,030
+1,296,030
+2,410,940
+2,488,740
+2,606,150
+2,658,370
+2,634,260
+2,569,550
+2,489,400
+2,467,940
+2,435,980
+2,306,180
+2,161,820
+2,026,660
+1,886,060
+1,736,460
+1,586,980
+1,436,330
+1,316,990
+1,174,730
299
-------
TABLE 5.6 (continued)
Calendar
year
(H
I960
61
62
63
64
65
66
67
68
Annual
discharge
in
acre-feet
(2)
51,093
17,220
73,705
23,361
3,129
1,662
31,778
3,608
19,150
Five-year
movi ng
average
in
acre-feet
(3)
22,260
24,510
38,280
35,720
33,700
23,820
26,730
12,710
11,870
Ten-year
moving
average
in
acre-feet
(4)
18,920
18,080
24,34o
24,640
23,460
23,040
25,620
25,4%
23,790
Departure
from
mean in
acre-feet
(5)
- 104,400
- 138,270
- 81,780
- 132,130
- 152,360
- 153,830
- 123,710
- 151,880
- 136,340
Accumulative
departure
from mean
in
acre-feet
(6)
+1,070,330
+ 932,060
+ 850,280
+ 718,150
+ 565,760
+ 411,930
+ 288,220
+ 136 , 340
0
46 Year Average:155,490
300
-------
Exploitation of groundwater was negligible before about
1900, when expanding population increased demand for all classes
of water use. Figure 5.1 shows irrigated areas in the Rio Grande
Valley. Groundwater use has expanded until about 90% of the
municipal and industrial use in 1969 and 1970 came from ground-
water (Lansford, et al.,1973). That use significantly affects
water table contours in several local areas. Figure 5.13 shows
one area with measured water level changes. Such changes often
reverse after pumping ceases.
Figure 5.14 shows the depth to groundwater in New Mexico.
Figure 5.15 outlines the major groundwater reservoir in the Rio
Grande Basin. In general, the water table contours follow the
land surface contours. Water moves from an area of higher head
(or potential energy) into an area of lower head, so that the
net movement is down the hydraulic gradient, and individual flow
paths intersect lines of equal potential at right angles. This
generally means that groundwater travels downhill from a moun-
tainous recharge area to a low discharge area such as a river
valley or lake.
5.5 CHEMICAL CHARACTERISTICS OF GROUNDWATER
Natural water quality depends on the type of rocks through
or over which the water travels. Water running over loose
sediments picks up particles and carries them as suspended
sediment (Fig. 5.16). Water in contact with soluble rocks
carries away part of the rock as dissolved solids (Fig. 5.17).
Dissolved solids are commonly reported in terms of parts
per million or milligrams per liter. The U.S. Public Health
Service (USPHS) defines saline water as water that contains more
than 1,000 mg/1 TDS, which equals one gram per liter (gm/1). The
Rio Grande Rift contains great volumes of saline water as
defined by the USPHS (Fig. 5.18). Kelly, et al. (1970) divided
the saline water category into four water quality ranges.
Following their scheme, slightly saline water contains 1 to 3
gm/1 TDS, moderately saline water contains 3 to 10 gm/1, very
saline water contains 10 to 35 gm/1 and brine contains more than
35 gm/1. For comparison, average sea water contains more than
35 gm/1, the Salton Sea in California contains 21 gm/1 and the
Dead Sea in Israel contains 315 gm/1 TDS (Krauskopf, 1967).
Slightly saline water is commonly used for drinking, irrigation
and industrial purposes in New Mexico where better quality water
is not available.
Saline gconridw&lrer in the rift area usually occurs below
potable groundwater, but the thickness of the fresh water zone
and the available volume of fresh water vary widely among
local areas in the rift. Figure 5.19 shows the thickness of the
fresh water unit in the Rio Grande Valley, and Figure 5.20 esti-
mates availability of fresh water.
301
-------
ft. T E.
ft. 8 E.
R.t E
H 10 E.
ft II C.
Contour showing decline
in water level, in feet.
Dashed where inferred.
Interval 5 feet.
Figure 5.13 Decline of groundwater. level in Estancia Basin,
Santa Fe and Torrance Counties, New Mexico,
1948-1960 . (Anonymous, 1967)
302
-------
, ,Mt
0 t S«.>.,,(.I I,,,,, ».,. ..,
EXPLANATION
L»«i tk«» tOO »«•! (00 t« 500 t««l M*rt IM* 500 l«tl »rt«» in .kick !«•••••
••••••4 t* k* tfr
Figure 5.14 Depth to groundwater in New Mexico .
(Anonymous, 1967)
303
-------
WMOXMUTC UlUTt OP TnK« VftTtR-KII
~ "
MMCTHM V ••«
OUINMC BASIN IMOEX
S-mo aMMOC
, 5 - TW.«OS<
I • 4 - JOWUM DEL MJCWTQ
KAI.C HI MLEt
Figure 5.15 Groundwater reservoir in the Rio Grande
Depression, New Mexico. (Anonymous, 1967)
304
-------
/ - " *> • « i _
$M'<" •«••!• « 1^
V* O f» * i II
,. _ ^ »\ MAUD MO
- • • T"
; HI DA L. a o
W—..-L.
I >"* , '
0 20 «O 60 SO M.m
EXPLANATION
Averoge suspended- ledimanl ditchargi
in tons per year. Magnitude of dit-
chargi represented by width of bar
Fioure 5.16 Average annual suspended sediment discharge of
streams and suspended sediment discharge by years
at selected stations in New Mexico. (Anonymous, 1965)
305
-------
- __^ if HA* O I N
r.'utumcofi I
QUAY !_„.
'0OfO»00 t^f'
I «'• ^Wt
CATRON'SOC
£ £
! I L I NfC,,O L N P
— -if- —I
jt^^m »,*ii.i.nf
flmr 1
•T i
EXPLANATION
Average annual dittolvtd solid* discharge in font
Magnitude of discharge represented by width of bar.
( Woft •• Vertical volutl en iflMt gropht rtttr to eittolvtd tolitft 4i«chargt in milliont o-f tent. )
Figure 5.17 Average annual dissolved solids discharge in years
-at selected stations in New Mexico (Anonymous, 1965)
306
-------
I O
t.
MIDALCO
-U..J?
S !
EXPLANATION
•• Midi* •«t«r »••••
,000-1,000
>,OOO- IO.OOO
W.OOO-ll.OOO
Ovir 35,000 M<"
Figure 5.18 General occurrence of saline groundwater in
New Mexico. (Anonymous, LVbi)
307
-------
EXPLANATION
Igneous and uplifted tedimentory
rocks that generally liove tow
yields of water to weds.
Line of equal saturated thickness
of fretrt- water unit. Intevol 500
ond 1000 feet.
ME tttf AOMTn FROM U.*. (EOLOCICAL XMVEY SA&E MAPS Q
or eoLORAOO •»), MEW MEXICO IWSOI.AND TEXM ises) i_
CO
tO MLB
Figure 5.19 Thickness of the fresh water unit (less than one gram
per liter dissolved solids). (Kelly, et al. 1970)
308
-------
»»•
!•••
!••• «t
-"-^l-l
r—-4—1_
-. J .. _ . . :\ •—
LOt
ALAMO*
: tANDOV
^ I « L t Y
JJ.
0 M 40 <0 W Win
n«t
CXPL ANATION
•MlM •
ftr •Mch
100 <• 300
M*r« HMH SOO
f»r •^rvlMl
Figure 5.20 General availability of relatively fresh ground-
water in New Mexico. (Anonymous, 1967)
309
-------
Human activities create wastes that sometimes enter the
water and significantly lower water quality. Figure 5.21 locates
several sources of waste water in New Mexico.
5.6 SEISMICITY
Seismicity in New Mexico is relatively low, about one-
eighteenth that of southern California and about one-tenth that
of Nevada (Slemmons, 1975).
Despite the fact that New Mexico was settled by the Spanish
in 1542, no earthquakes were reported until 1849 (Northrop,
1976). This is indicative of the poor earthquake history of New
Mexico which is due in part to the lack of instrumentation to
record even a moderate event and in part to a sparsely distrib-
uted population throughout most of New Mexico.
Instrumental studies of New Mexico started in June 1960,
when high magnification seismographs were put into operation by
the New Mexico Institute of Mining and Technology at Socorro and
by the Atomic Energy Commission at Sandia Base near Albuquerque.
More high gain stations were placed in operation from 1962 on,
and availability of data from several stations, rather than one
or two, increased the accuracy of location and magnitude deter-
minations. However, the relatively short period of instrumental
records makes it extremely difficult to derive reliable long-
term earthquake recurrence statistics.
5.6.1 Seismicity Along the Rio Grande Rift
The Rio Grande Rift has been structurally active for thou-
sands of years, but earthquake activity does not appear to be
limited to major faults. Large earthquakes reported in New
Mexico during the hundred-odd years for which records have been
kept occurred almost exclusively in the Rio Grande Rift. Only
one strong shock occurred outside the rift from 1869 to 1960,
while nine were reported within the rift (Sanford, et al., 1972).
The distribution of seismic activity in the Rio Grande Rift
is fairly well established. Historical reports and recent
instrumental studies indicate that most of the shocks have been
centered near Socorro. Northrop (1976) reports that/ of 523
definitely recorded earthquakes with epicenters in New Mexico
from 1849 to 1975, 76% occurred within the rift, and of those,
96% were restricted to the 121 km (75 mi) long segment between
Albuquerque and Socorro. Instrumental data from earthquakes
with local magnitudes (ML) (Richter, 1958) greater than 2.7
places the zone of highest activity in the rift south of Socorro
to Las Cruces. Instrumental data from microearthquakes
(M,> 2.7) places the highest activity in the rift near Socorro
(Sanford, et al.,1972). Sanford, et al.,(1972) show that on
310
-------
-i-,..
".
I *
I S A N J^ u A
• ' »ANOOv»L /**«*•'£ I
«- « r | jf/1 C» I
• A N T A | V^"^ SAN M I O U
-V--AH
r-ucumcin i
QUAY l_
—: 7
1..
S i
EXPLANATION
mills
Oil (i«ldi
krlut
Nuclear «n*r«y lak»rit«rit«
Figure 5.21 Principal sources of waste water in New Mexico.
(Anonymous, 1965)
311
-------
the average about 400 earthquakes are recorded each year with
magnitudes above 0 and epicenters within 20 km (12.5 mi) of
Socorro.
The relatively short record of earthquake activity in New
Mexico makes it difficult to accurately appraise the long-term
level of activity. Recent instrumental work, including micro-
earthquake surveys, indicates a modest degree of seismicity with
a maximum MT magnitude of 4.2 to 4.9 (Sanford, et al., 1972). On
the other hand, historical records show that at least one shock
in excess of magnitude 6 has occurred in the rift within the
last 100 years (Sanford, et al.,1972). Northrop (1976)
predicts a shock of magnitude 6 between Socorro and Albuquerque
once every 100 years and a shock of magnitude 5.5 near Los
Alamos once every 100 years.
Study of faults cutting and displacing recent geomorphic
features such as pediments, alluvial fans and stream drainages
can also provide an estimate of the area's seismic activity.
The wide variation in ages assigned to these geomorphic features
causes a variation in the predicted maximum shock in a 100-
year period. Even so, the maximum magnitude earthquake pre-
dicted for a 100- year period ranges from 4.6 to 6-6 and thus
falls in the range of predictions based on microseismic data or
historic reports. Using an intermediate age of less than 40,000
years for the fault scarps cutting recent geomorphic features
gives a magnitude of 5.6 for the maximum earthquake in a 100-
year period.
Separate data sources agree in general on the area of
greatest seismic activity but do not agree in detail. Likewise,
the prediction of seismic risk varies among the methods. The
highest risk, a maximum earthquake of about magnitude 6 in a
100-year period, comes from historical data; the lowest of
about 4.6 comes from microseismic data, with instrumental data
from earthquakes giving a maximum magnitude of about 5. Because
historical data considers a longer period, it probably produces
the best available current estimate of seismic risk.
The New Mexico region of the seismic risk maps prepared by
Richter (1956) and Algermissen (1969), are reproduced here as
Figures 5.22 and 5.23. Note that Richter's map shows a zone of
high seismic risk in central New Mexico, extending along the Rio
Grande, in which earthquakes of intensity IX may occasionally be
expected. However, Algermissen1s map suggests only earthquakes
of intensity V and VI in eastern New Mexico. Sanford, et al.
(1972) conclude that Richter's estimate of seismic risk for the
Rio Grande Rift Zone appears to be too high and Algermissen's
too low.
312
-------
(occasional)
(occasional)
\
Figure 5.22
Seismic risk map by Richter (1958).
(Intensities according to Modified Mercalli
Intensity Scale of 1931)
313
-------
Figure 5.23 Seismic risk map by Algermissen (1969).
(Intensities according to Modified Mercalli
Intensity Scale of 1931)
314
-------
5.6.2 Seismicity of the Valles Caldera Region
Valles Caldera lies in the Jemez Mountains along the west-
ern margin of the Rio Grande Rift. The Jemez Mountains, a
complex of Tertiary and Quaternary volcanics, are genetically
associated with the formation of the Rio Grande Rift structure.
Purtyman and Jordan (1973) have noted that this geologic regime
could produce seismic activity by rupture along faults bounding
the rift or by failure of rocks in the Valles Caldera as a
result of expansion and movement of magmas along volcanic vents
in the Valles Caldera Volcanic Field. However, several authors
(Newton, et al., 1976; Slemmons, 1975; Sanford, 1976) have noted
the surprisingly low seismicity in the Jemez Mountains. Sanford
(1976) reviews the seismicity within a radius of 111 km (69 mi)
of Los Alamos for a period of 100 years. Pre-1962 earthquakes
are based mainly on historical data. During the 14 years
of instrumental observation, 75% of the shocks occurred within
the Rio Grande Rift, but the Valles Caldera experienced no
seismic activity above the ML = 2.5 level. The largest shock
reported in the Jemez Mountains for the 100-year study was a
felt earthquake of magnitude 4.0, located directly under Los
Alamos on August 17, 1952.
The strongest earthquake within the 111 km (69 mi) radius of Los
Alamos was the Cerrillos earthquake of May 28, 1918, located
approximately 60 km (37 mi) southeast of Los Alamos. The shock
had an energy release of about 14 times the combined energy
release of all other shocks within the 111 km (69 mi) radius of
Los Alamos during the 100-year period (Sanford, 1976).
Sanford (1976) estimates the recurrence interval for a
magnitude 5.5 earthquake once every 100 years for the part of
the Rio Grande Rift from Albuquerque to Questra, the limits of
the 111 km radius from Los Alamos within the rift. This implies
that the seismicity of Los Alamos region is somewhat less than
the seismicity of the Albuquerque to Socorro segment of the rift
and only one-eighteenth that of the recurrence interval in
southern California (Slemmons, 1975).
Sanford (1976) notes a period of relatively high seismic
release within the Los Alamos area during the years 1930-31
and 1947-56. Excepting these two periods of high energy
release, Sanford's (1976) data appears to indicate a steady
decline in seismic energy, release for the Los Alamos region
since 1918 and a slight increase since 1970 Sanford states
that this could be the beginning of a period of relatively
accelerated seismic activity similar to that observed during the
periods of high seismicity.
315
-------
Sanford (1976) concludes that his estimate for seismic risk
is based upon the assumption that seismic activity will continue
at the same level as observed in the past 100 years and esti-
mates the magnitude of the strongest earthquake to occur within
a 111 km (69 mi) radius of Los Alamos during a 100-year period
as M, = 5.5, producing effects up to intensity VII. He gives a
probability of 0.08 for this earthquake to occur within the 111 km
(69 mi) radius of Los Alamos, based on the assumption that the shock
has equal probability of occurring anywhere within the Rio
Grande Rift.
316
-------
REFERENCES
Algermissen, S. T. Seismic Risk Studies in the United States;
in Proc. of the Fourth World Conference on Earthquake
Engineering. Asociacion Chilena de Sismologiae Ingenieria
Antismica, Santiago, Chile, v. 1, p. 14-27, 1969.
Anonymous. Water Resources of New Mexico: Occurrence, Develop-
ment and Use. State Planning Office, Santa Fe, New Mexico,
321 p., 1967.
Bridwell, R. J. Lithospheric Thinning and Late Cenozoic Thermal
and Tectonic Regime of the Northern Rio Grande Rift. New
Mex. Geol. Soc., Guidebook 27th Field Conf., p. 283-292,
1976.
Chapin, C. E. The Rio Grande Rift, Part I: Modifications and
Additions. New Mex. Geol. Soc., Guidebook 22nd Field
Conf., p. 191-201, 1971.
Cordell, L. Aeromagnetic and Gravity Studies in the Rio Grande
Graben in New Mexico Between Belen and Pilar. New Mex.
Geol. Soc., Spec. Pub. No. 6, p. 62-70, 1976.
Jetton, E. V./ and J. W. Kirby. A Study of Precipitation,
Streamflow, and Water Usage on the Upper Rio Grande.
Atmospheric Science Group, University of Texas at El Paso,
Report No. 25, 203 p.,1970.
Kelley, V. C. Tectonics of the Rio Grande Depression of Central
New Mexico. New Mex. Geol. Soc., 3rd Field Conference, p.
93-105, 1952.
. Tectonic Map of a Part of the Upper Rio Grande
Area, New Mexico. Oil and Gas Inv., Map No. OM 157, 1954.
Kelly, T. E., B. N. Myers and L. A. Hershey. Saline Ground
Water Resources of the Rio Grande Drainage Basin, a Pilot
Study. Office of Saline Water, Research and Development
Progress Report, No. 560, Los Angeles, 1970.
Krauskopf, K. B. Introduction to Geochemistry. McGraw-Hill,
Inc., 721 p., 1967.
317
-------
Lansford, R. R., S. Ben-David, T. G. Gebhard, Jr., W. and C.
Brutsaert and J. Bobby. An Analytical Interdisciplinary
Evaluation of the Utilization of the Water Resources of the
Rio Grande in New Mexico: Socorro Region. New Mex. Water
Res. Inst. Report No. 023, 1973.
Newton, C. A., D. J. Cash, K. H. Olsen and E. F. Homuth. Los
Alamos Scientific Laboratory Seismic Program in the Vicin-
ity of Los Alamos, New Mexico. Los Alamos Scientific
Laboratory Informal Report No. LA-6406-MS, 1976.
Northrop, S. A. New Mexico's Earthquake History 1849-1975; in
Tectonics and Mineral Resources of Southwest North America.
New Mex. Geol. Soc. Spec. Pub. No. 6, p. 77-87, 1976.
Purtyman, W. D., and H. S. Jordan. Seismic Program of the Los
Alamos Scientific Laboratory. Los Alamos Scientific Labor-
atory Pub. No. LA-5595-MS, 1973.
Reddy, R. S. Crustal structure in New Mexico. M.S. thesis, New
Mex. Inst. of Mining and Tech., unpub., 1966.
Reiter, M., C. L. Edwards, H. Jartman and C. Weidman. Terres-
trial Heat Flow along the Rio Grande Rift, New Mexico and
Southern Colorado. Bull. Geol. Soc. Am., v. 86, p. 811-
818, June 1974.
Richter, C. F. Elementary Seismology. W. H. Freeman and
Company, Inc., 786 p., 1958.
Sanford, A. R. Seismicity of the Los Alamos Region Based on
Seismological Data. Los Alamos Scientific Laboratory
Information Report No. LA-6416-MS, 1976.
Sanford, A. R., A. J. Buddington, J. P. Hoffman, 0. S. Alptekin,
L. A. Rush and T. R. Toppozada. Seismicity of the Rio
Grande Rift in New Mexico. New Mex. Bur. of Mines and
Mineral Res., Circ. 120, 1972.
Sanford, A. R., et al. Micr©earthquake Investigation of Magma
Bodies in the Vicinity of Socorro, New Mexico (abs.).
Geol. Soc. Am. Abs. with Program, p. 1085, 1976a.
Sanford, et al. Geophysical Evidence for a Magma Body in the
Crust in the Vicinity of Socorro, New Mexico. Paper pre-
sented at the ONR-CSM Symposium on "The Nature and Physical
Properties of the Earth's Crust," Vail, Colorado, Aug. 2-6,
1976b.
Slemmons, D. B. Fault Activity and Seismicity Near the Los
Alamos Scientific Laboratory Geothermal Test Site, Jemez
Mountains, New Mexico. Los Alamos Scientific Laboratory
Informal Report No. LA-5911-MS, 1975.
318
-------
Shuleski, P. J., F. J. Caravella, E. J. Rinehart, A. R. Sanford,
T. C. Wallace and R. M. Ward. Seismic Studies of Shallow
Magma Bodies Beneath the Rio Grande Rift in the Vicinity of
Socorro, New Mexico. Geol. Soc. Am. Abs. with Program, v.
9, No. 1, p. 73, 1977.
Stone, W. J., and N. B. Mizell. Geothermal Resources of New
Mexico — a Survey of Work to Date. New Mex. Bur. of Mines
and Mineral Res., Open File Report 73, 117 p., 1977.
Summers, W. K. A Preliminary Report on New Mexico's Geothermal
Energy Resources. New Mex. Bur. of Mines and Mineral Res.,
Circ. 80, 41 p., 1965.
Catalog of Thermal Waters in New Mexico. New Mex.
Bur. of Mines and Mineral Res. Hydrology Report 4, 80 p
1976.
Woodward, L.A., J. F. Callender, J. Cries, W. R. Seager, C. E.
Chapin, W. L. Shaffer and R. E. Zilinski. Tectonic Map of
Rio Grande Region from New Mexico-Colorado Border to Pre-
sidio, Texas. New Mex. Geol. Soc., Guidebook 26th Field
Conf., p- 239, 1975.
319
-------
APPENDIX A. GEOLOGIC TIME SCALE (Slemmons, 1975)
MAJOR STRATIGRAPHIC AND TIME DIVISIONS
Subdivisions In Use By The U. S. Geological Survey
Era Or
Era them
Cenozoic
Mesozoic
Paleozoic
Precambrian
System Or Period
Quaternary
Tertiary
Cretaceous
Jurassic
Triassic
Permian
Pennsylvanian
Mississippian
Devonian
Silurian
Ordovician
Cambrian
Series Or Epoch
Holocene
Pleistocene
Pliocene
Miocene
Oligocene
Eocene
Paleocene
Upper (Late)
Lower ^Early)
Upper (Late)
Middle (Middle)
Lower (Early)
Upper (Late)
Middle (Middle)
Lower (Early)
Upper (Late)
Lower (Early)
Upper (Late)
Middle (Middle)
Lower (Early)
Upper (Late)
Lower (Early)
Upper (Late)
Middle (Middle)
Lower (Early)
Upper (Late)
Middle (Middle)
Lower (Early)
Upper (Late)
Middle (Middle)
Lower (Early)
Upper (Late)
Middle (Middle)
Lower (Early)
Time Subdivisions Of The Precambrian
Precambrian Z — base of Cambrian to 800 m.y.
Precambrian Y — 800 m.y. to 1600 m.y.
Precambrian X — 1600 m.y. to 2500 m.y.
Precambrian W — older than 2500 m.y.
Age Estimates Commonly
Used For Boundaries (In
Million Years)
<•>
f *"
?On
-430-440
— ca. 500—
(b)
* 0
C f
Geol. Soc. London, The Panerozoic Time-Scale, A Symposium, Geol. Soc. London, Quart.
Journ. 120, Suppl., 260-262, 1964 .
W. A. Berggren, A Cenozoic Time Scale — Some Implications for Regional Geology and
Paleobiogeography, Lethaia 5 No. 2, 195-215^1972 .
. p
Slemmons, D.B. Fault Activity and Seismicity near the
Los Alamos Scientific Laboratory Geothermal Test Site,
Los Alamos Scientific Laboratory Informal Kept, LA-5911-MS,
1975-
320
-------
U.S. CUSTOMARY
APPENDIX B. U.S.-METRIC CONVERSION TABLE
U.S. EQUIVALENT METRIC EQUIVALENT
inch (in)
inch
foot (ft)
yard (yd)
mile (tni)
square foot (sq ft)
square yard (sq yd)
acre
acre
square mile (sq mi)
gallon
acre-foot (acre-ft)
acre-foot/acre
cubic feet (cu ft)
cubic mile (cu mi)
gallons per second
gallons per minute (gpm)
gallons per day (gpd)
gallons per minute/foot
(gpm/ft)
gallons per day/ft
(gpd/ft)
18.2 gpd/sq ft
pounds per hour
cu ft per sec (cfs)
Length
0.082 ft
"0.083 ft
0.33 yd, 12 in
3 ft, 36 in
5,280 ft, 1,760 yd
Area
144 in
1,294 sq in, 9 sq ft
43,560 sq ft, 4,840 sq yd
43,560 sq ft, 4,840 sq yd
640 acres
Volume
4 quarts
325,850.28 gallons
Flow Rate
Darcy
25.4 millimeters (mm)
"2.54 centimeters (cm)
0.3048 m3534 (m)
0.9144 m
1.609 kilometer (km)
0.0929 sq m
0.836 sq m
4,047 sq m
0.4046 hectare (ha)
2.59 sq km
3.785 liters (1)
0.12335 hectare-meter
(ha-m)
0.3048 ha-m
0.02832 cubic meter
(cu m)
4.1655 cu km
3.785 liters per second
(IPS)
3.785 liters per minute
(1pm)
3.785 liters per day
(Ipd)
12.418 Ipm/m
12.418 Ipd/tn
8.58 x I0~k cm/sec
1.262 x lQ~k kg/sec
28.32 Ips
321
-------
U. S. CUSTOMARY
U. S. EQUIVALENT
Miscellaneous
pounds per square inch (psi)
pounds per square inch (psi)
British Thermal Unit (BTU)
BTU/lb
ounce
pound
ton
METRIC EQUIVALENT
9/5 (°C) + 32
(°F - 32) 5/9
0.7031 gm/sq cm
0.0689 bar
1,055 joules (J)
2,325.84 J/kg
28.35 grams
0.4536 kilogram (kg)
0.907 metric ton
322
-------
APPENDIX C
BASIC CONCEPTS AND SEMANTICS OF HYDROLOGY
The basic premise of groundwater hydrology is that under
natural conditions part of the precipitation that falls in an
area moves from the land surface down an energy gradient to the
water table where it enters the zone of saturation. It then
moves through the zone of saturation until it leaves this zone
so that it may (1) enter the overlying unsaturated zone, (2)
become stream flow, or (3) become vapor and move directly to the
atmosphere.
By definition, only the water in the zone of saturation is
properly called groundwater. The precipitation that moves to
the water table is called recharge and the area over which
percolation to the water table occurs is called the recharge
area. Water in the groundwater reservoir is said to b~ein
transient storage. The water that leaves the zone of saturation
is called discharge, and the area over which discharge occurs is
called the discharge area.
Under natural conditions, over a long period of time, a
state of dynamic equilibrium exists in which recharge equals
discharge and the volume of water in transient storage remains
constant (or more precisely fluctuates about a mean).
Because modern hydrologists recognize that under natural
hydrodynamic conditions the water moves through the unsaturated
zone, they now consider groundwater flow systems to include
both saturated and unsaturated flow, so for this report the
groundwater flow system shall be used in this larger context.
The water in a natural groundwater flow system has chemi-
cal characteristics that depend upon its position in the system
and upon the kind of rock through which it flows. The systems
are three dimensional, and flow may be across bedding or strati-
graphic units as well as parallel to them, so the chemical
character of water in a formation does not necessarily reflect
chemical changes due exclusively to flow through that formation.
In natural discharge areas, groundwater near or at the
surface tends to discharge primarily via evapotranspiration.
Local surface buildup of dissolved solids occurs simply because
the residual water is enriched in soluble salts.
323
-------
ENERGY
The energy to drive the water from the recharge area to the
discharge area is primarily the potential energy due to gravity
acting upon the mass of water.
In general, the energy at a point in a groundwater flow
system is expressed as the sum of (1) a quantity that is a
function of the mass of water, its altitude, and the gravita-
tional constant at the point, and (2) a quantity that is a
function of the pressure exerted by the water at the point. The
pressure depends in turn on a number of factors. However, by
assuming (1) a gravitational constant, (2) water of uniform
density, and (3) no unusual source of pressure (such as electro-
osmotic phenomena) one may represent the energy at any point in
a groundwater flow system by associating with that point the
altitude to which water would rise above the given point. This
altitude is generally referred to as the head or potential. For
the zone of saturation this altitude would be the altitude of
the water level in a piezometer open only at the point. In the
unsaturated zone, the determination of the value is much more
difficult since capillary pressure must be measured and
accounted for. At the boundary between the unsaturated zone and
the zone of saturation there exists a capillary fringe. We,
therefore, define the water table arbitrarily as the surface
through those points where the pressure is equal to local atmos-
pheric pressure. At this surface and below, the effects of
capillarity become negligible. Because head consists of an
altitude term and a pressure term, groundwater may move from
low to high pressure as well as high to low pressure.
HYDRAULIC GRADIENT
The energy gradient, or hydraulic gradient as it is gene-
rally called, is a statement of the rate of change of energy
along a given flow path. It may be considered to have two
components, one horizontal, the other vertical. Where the verti-
cal component is directed downward, the flow is downward; where
it is directed upward, the flow is upward.
Recharge occurs where the vertical component of the hydrau-
lic gradient is directed downward. In this region the water
table is concave downward.
Discharge occurs where the vertical component of the hy-
draulic gradient is directed upward. In this area the water
table is concave upward. The line along which the vertical
component is zero is an inflection line on a water table map and
can be used to distinguish the recharge from the discharge
areas.
324
-------
Since flow occurs in response to an energy gradient, hori-
zontal flow through the unsaturated zone is possible and should
never be categorically assumed to be negligible. Because ver-
tical hydraulic gradients exist, the shape of the water table
should be considered only a guide to the near-surface ground-
water flow direction.
DIVIDES
Groundwater flow is three-dimensional. Therefore, in any
natural groundwater flow situation under dynamic equililibrium
there exists a series of surfaces that extend from the recharge
area to the discharge area in such a way that for the flow above
the surface, recharge equals discharge. These surfaces are
called divides. Between divides recharge equals discharge. At
the land surface, the groundwater divide need not follow sur-
face drainage basin divides.
NATURAL GROUNDWATER FLOW SYSTEMS
Natural groundwater flow systems may be classified as
simple or complex. They are also classified as local, inter-
mediate or regional. A simple or local flow system involves
recharge and discharge over a relatively small area, relatively
short flow paths and shallow depth of circulation. Recharge
occurs over an essentially continuous area. Discharge derives
exclusively from nearby recharge.
A complex or intermediate flow system involves recharge and
discharge over a larger area than a local flow system. Flow
paths are longer. Circulation extends to greater depths. Re-
charge areas are not continuous; consequently at least one local
flow system is evident.
The most complex flow system is the regional system, which
includes recharge and discharge over large areas and contains some
very long flow paths that underflow at least one intermediate
flow system and one local flow system.
Based on studies of (1) the distribution of head, (2)
hydrogen-oxygen isotopes, (3) geochemistry of groundwater, (4)
age of groundwater, (5) oceanic discharge of groundwater, and
(6) paleohydrologic systems, we know that groundwater flow
systems may extend to depths that reach to thousands of feet
below sea level.
325
-------
GROUNDWATER FLOW THROUGH ROCKS
If we examine rocks closely, we find that they are made up
of solid mineral grains, interconnected pores and isolated
pores. Water flows through the interconnected pores. These
pores may be classified as intergranular, fracture or tubular.
Intergranular pores are pores between minerals or other
rock - forming particles. The ratio of the shortest to the
longest dimension ranges from about 1:1 to 1:5. Usually the
pore dimensions of intergranular pores are measured in microns
or millimeters.
Fracture pores are all those planar pores such as bedding
planes and cracks that develop in response to stresses (e.g.,
faults, sheetings, columnar joints). These pores have two very
long dimensions and one very short dimension. The long dimen-
sion is usually measured in meters or tens of meters, whereas
the short dimension is usually measured in millimeters or tenths
of a millimeter.
Tubular pores include such features as solution cavities
and lava tubes as well as a host of trivial near-surface phenom-
ena such as worm tubes. They may also include such items as
geyser tubes and man-made wells or bore holes. Tubular pores
have two relatively short dimensions and one very long dimen-
sion. The short dimensions are usually measured in centimeters
or meters, whereas the long dimension is generally measured in
hundreds of meters or even kilometers.
TRANSIENT WATER LEVELS
Although a natural groundwater flow system may be in
dynamic equilibrium when considered for a long period of time,
there may be substantial departures from equilibrium for periods
ranging from a few minutes to a few years.
During these transient periods/ water is taken into or
discharged from storage and associated water level changes
occur.
Short -term changes in storage occur because pressure
changes cause an elastic response in the rock so that water is
taken into or released from storage with no change in the posi-
tion of the water table. Changes of this sort are brought on by
air pressure changes, tidal fluctuations, earthquakes, short
term loading or unloading, and pumping from or injecting into
wells. These water level changes are here referred to as
elastic-storage transients.
326
-------
When the works of man—such as the installation of a well
construction of a dam or the creation of a sustained synthetii
recharge condition-create a long-term changefnthe flw
^^;vt^n;alast^c-st?ra?e transients are noted first and then
porosity-storage transients become evident. Finally, if the new
condition is sustained for a sufficiently long period a new
i££ w«t£W ^ * iS Crea,ted ^ is in dynamic equilibrium.
The water table shape adjusts to fit the new equilibrium.
Energy distribution around the new feature also adjusts until a
fixed divide becomes evident and measurable. in those cases
where there are many wells or there are many recharge points,
the short-term transients associated with individual wells will
mask the developing long-term equilibrium of the new flow system.
GROUND WATER MANAGEMENT CONCEPTS
The works of man—wells, irrigation systems, mines and
excavations, dams, drains and canals, sewage disposal facili-
ties, etc.—alter natural groundwater systems by changing the
location and amount of recharge and/or discharge, and by chang-
ing the energy distribution in the groundwater reservoir.
Management of a groundwater resource consists of controlling
the discharge and recharge rates and durations from or the
energy (water level) distribution within the groundwater reser-
voir, or both, through the use of the works of man.
Management of a groundwater reservoir takes into account
the consequence of changes in the discharge-energy relationship
as a function of time that are a consequence of the works of
man. Management may also take into account the changes in water
chemistry and temperature of the water as a function of time due
to the works of man.
SAMPLE TYPES
Two types of chemical analyses of groundwater are
available.
The most common one is the analysis made to establish the
character of the water as it will be used. These are water
quality analyses. The other type is rather rare for it reveals
(hopefully) the chemical character of the water in the ground.
These are hydrogeochemical analyses.
If the water sample represents only a small portion of the
flow continuum, and the water sample did not age, it can be
considered a hydrogeochemical analysis. Sometimes water quality
analyses will meet these criteria.
327
-------
If we know the chemical character of the water in the
ground, we can predict the chemical character of the water as it
will be used. The inverse is not necessarily true. A monitor-
ing program should define the chemical character of the water in
the rocks as a function of time.
328
-------
APPENDIX D
GLOSSARY
alluvium: Relatively unconsolidated detrital material (clay,
silt, sand, gravel) deposited in comparatively recent geo-
logic time by flowing water.
aquiclude: Relatively impermeable strata that absorbs water
slowly and functions as a boundary of an aquifer. It does
not transmit ground water quickly enough to supply a well
or spring. Clay or shale beds and faults often act as
aquicludes.
aquifer: A body of rock or sediment that contains sufficient
saturated permeable materials to conduct ground water and
yield significant quantities of ground water to wells and
springs.
aquitard: Confining strata that retards the flow of water but
does not prevent flow to or from an adjacent aquifer.
artesian water: Ground water confined under hydrostatic pres-
sure. Water in an artesian well rises above the level of
the water table underartesian pressure, but does not
necessarily reach the land surface. The term is sometimes
restricted to mean only a flowing artesian well.
Bouguer anomaly: A gravity value calculated by allowing for the
attraction effect of topography but not for that of iso-
static compensation.
brine: A solution containing more than 3.5% total dissolved
solids (35,000 mg/1). This is the approximate TDS of sea
water.
caprock (geothermal): A relatively impermeable rock layer over-
lying a hot water or steam reservoir which prevents the
heat or fluid from directly migrating or dissipating upward
to the surface.
clast: A rock fragment produced by mechanical weathering of a
larger rock mass.
329
-------
conductive heat flow: Heat transfer from a higher-temperature
to a lower-temperature region by molecular impact
(vibration) without transfer of matter itself.
convective heat flow: Mass transfer of heat due to temperature-
caused density gradients, e.g., circulation of hot water in
a convecting geothermal reservoir.
connate water: Water trapped, at the time of deposition, in the
interstices of a sedimentary or extrusive igneous rock.
contour line: A line that passes through all consecutive points
of equal value for a parameter which is variable, e.g.,
topographic elevation, ground water level or temperature.
craton: A part of the earth's crust which has attained stabil-
ity and which has been little deformed for a prolonged
period.
deuterium: The hydrogen isotope that occurs in water and has
twice the mass of ordinary hydrogen. It is also called
heavy hydrogen and its chemical symbol is "D".
diktytaxitic: Rock texture of some olivine basalts in the
Pacific Northwest, characterized by numerous jagged, ir-
regular vesicles bounded by crystals.
effluent: Flowing forth or out, emanating: 1) a surface stream
that flows out of a lake or larger stream, 2 ) a liquid
discharged as waste.
electrical resistivity survey: A geophysical exploration tech-
nique where electric current is artificially introduced
into the ground and the distribution of current below the
surface is measured by electrodes separated by increasing
increments. Depths to geologic interfaces may be deter-
mined by plotting apparent resistivity versus electrode
separation.
eutrophication: The artificial or natural enrichment of a lake
by an influx of nutrients required for the growth of
aquatic plants.
fault: A surface or zone of rock fracture along which there has
been displacement, from a few centimenters to hundreds of
kilometers in scale. Faults are classified according to
the relative motion of the rock on each side of the frac-
ture zone, or fault plane. These classifications are
illustrated below in the diagrams of fault types.
330
-------
STRIKE -SLIP NORMAL REVERSE ROTATIONAL TRANSFORM
fault scarp: A fairly steep slope or cliff formed directly by
movement along one side of a fault and representing the
exposed surface of the fault plane before modification by
erosion and weathering.
fumarole: A volcanic vent from which gases and vapors are
emitted; it is characteristic of a late stage of volcanic
activity.
geomorphology: The science of the earth's surface; specifically
the classification, description, origin and development of
present land forms and their relationships to underlying
structures.
geosyncline (variety eugeosyncline, miogeosyncline): An
elongate crustal depression or basin, often subsiding,
where thousands of meters of sediment accumulate, usually
in some phase of a marine environment.
geothermal gradient (temperature gradient): The rate of in-
crease of temperature in the earth with depth. The average
gradient is approximately 1°C per 30 m (2°F per 100 ft).
geothermometry (geologic thermometry): 1) The science of the
earth's heat; 2) a mineral or mineral assemblage whose
characteristics are fixed within known thermal limits thus
allowing conclusions about temperatures during process of
formation, e.g., sodium, potassium and calcium concen-
trations in natural waters may be used to predict the last
temperature of water-rock equilibration.
graben: A crustal block that is bounded by faults on its long
sides, the block being downdropped in relation to the
surrounding land.
groundwater: Subsurface water, especially that contained in a
saturated zone, or strata, including underground streams.
horst: A crustal block that is bounded by faults on its long
sides, the block being uplifted in relation to the sur-
rounding land.
331
-------
hydraulic gradient: In an aquifer, the rate of change of pres-
sure head (height of a column of water that the pressure
can support) per unit of distance of flow at a given point
and in a given direction. It is usually expressed in
meters per kilometer or feet per mile.
hydrologic budget (variety water budget): An accounting of the
inflow to, outflow from, and storage in, a hydrologic unit,
e.g., drainage basin, aquifer or reservoir; the relation-
ship between evaporation, precipitation, runoff and change
in water storage is implied.
hydrology: The science that deals with all properties of water
(liquid and solid) on, under and above the earth's surface.
hydrothermal: Pertaining to heated water (or aqueous solution)
or products resulting from heated water, i.e., alteration
of rocks or minerals by reaction of hydrothermal water.
igneous rock: A rock that solidified from molten or partly
molten material, i.e., from a magma. Intrusive - usually
having visible crystal components, and formed deep under
the earth's surface, e.g., granite, diorite, gabbro, peri-
dotite. Extrusive - an igneous rock that solidified on or
near the surface, e.g., rhyolite, andesite, basalt (lava
flows).
inflow: The act or process of flowing in, e.g., the flow of
water into a drainage basin.
inlier: An area or group of rocks surrounded by outcrops of
younger rocks.
intensity (of an earthquake): A subjective measurement rating
the severity of ground motion at a specific site during an
earthquake. The Modified Mercalli scale uses Roman
numerals from I to XII to describe the motion that was
felt and the damage to man-made structures. Intensity at a
point depends not only upon the strength of an earthquake
(the earthquake magnitude), but also upon the distance to
the earthquake epicenter and the geologic and soil condi-
tions at the point.
intrusion: The injection of magma into preexisting rock, re-
sulting in plutpns, batholiths and laccoliths (large
scale) or stocks, dikes and sills (small scale).
isotherm: A line connecting points of equal temperature.
332
-------
isotope ratios: Isotope abundances given as a ratio relative to
a standard rather than an absolute. Different ratios can
indicate changes in environment or origin for a given
chemical element. The standard is often Standard Mean
Ocean Water (SMOW). Some common ratios are defined as
follows:
6018(in °/00) = f(0 /0 ^ample _ 1 ^
L(018/016)
u } Standard -»
Similar definitions exist for ratios of deuterium(D)
to hydrogen (H) and for C14 to C12
juvenile water: Water derived directly from a magma, reaching
the earth's surface for the first time.
KGRA: Known Geothermal Resource Area - a legally defined land
area that is considered to have potentially economic geo-
thermal resources.
Langelier-Ludwig diagram: A diagram representing groupings of
chemical composition of aqueous solutions.
lithic fragment: A fragment from a preexisting rock mass,
usually used in describing a medium-grained sedimentary
rock or certain types of volcanic deposits.
mafic: Generally igneous or volcanic rocks, containing iron,
magnesium and other dark-colored minerals.
magnetic survey: Measurement of a component or element of the
geomagnetic field at different locations. It is usually
made to map either the broad patterns of the earth's main
field or local anomalies due to variation in rock magneti-
zation. It is often conducted as an aeromagnetic survey.
magnetotelluric survey (MT): An electromagnetic method in which
natural electric and magnetic fields are measured; usually
two-dimensional horizontal electric field and three-dimen-
sional magnetic field components are recorded.
magnitude (earthquake): A measure of the strength of an earth-
quake or the strain energy released by it, as determined by
seismologist C.F. Richter, who first applied it to southern
California earthquakes. For that region he defined local
magnitude as the logarithm, to the base 10, of the ampli-
tude in microns of the largest trace deflection that would
be observed on a standard torsion seismograph (static
magnification = 2,800, period =0.8 sec, damping constant =
0.8) at a distance of 100 km from the epicenter. Magni-
333
-------
tudes determined at teleseismic distances using the
logarithm of the amplitude to period ratio of body waves
are called body-wave magnitudes and using the logarithm of
the amplitude of 20-sec period surface waves are called
surface-wave magnitudes. The local body-wave and surface-
wave magntidues of an earthquake will have somewhat differ-
ent numerical values.
melange: A mixture of rock materials derived from more than one
depositional realm, usually sheared and deformed. It is a
mappable body, sometimes several kilometers in length.
metamorphic rock: Rock resulting from once solid, preexisting
rock subjected to extreme heat, pressure or chemical
changes, e.g., slate, schist, greiss, quartzite, marble,
serpentine.
meteoric water: Water of atmospheric origin, e.g., rain.
microearthquake: An earthquake having a magnitude of two or
less on the Richter scale (cutoff may vary accoridng to
user).
Mohorovicic discontinuity (moho): A sharp seismic-velocity
discontinuity that separates the earth's crust from the
subjacent mantle. Its depth varies from 5 to 10 tan (8 to 16 mi)
beneath the ocean floor to about 35 km (55 mi) below the
continents.
nanoearthquake: An earthquake having a magnitidue of zero or
less on the Richter scale (cut off may vary according to
user.)
outflow: The act or process of flowing out, e.g., ground water
seepage and stream water flowing out of a drainage basin.
pediment: Gently inclined erosion surface carved in bedrock,
with a thin veneer of alluvium derived from the upland
masses and in transit across the surface. Pediments occur
between mountain fronts and valley floors.
percent reactance: The ratio of one anion species to the total
anion species, expressed in milliequivalents per liter, and
similarly for cation species. For example, if a water
contains 0.8 meq/1 Ca and the sum of all the cation species
is 13.7 meq/1 then the percent reactance Ca would be
0.8/13.7 or 6%. This expression provides a method of "nor-
malizing" chemical analyses for data having a wide range of
concentrations.
334
-------
perched water table: Unconfirmed ground water separated from an
underlying main body of ground water by an aquiclude and an
unsaturated zone.
permeability: Ability of a rock, sediment or soil to transmit a
fluid without impairment of the structure of the medium. A
measure of the relative ease of fluid flow under unequal
pressure. The customary unit of measurement is the darcy.
It is equivalent to the passage of one cubic centimeter of
fluid of one centipore viscosity flowing in one second
under a pressure differential of one atmosphere through a
porous medium having a cross sectional area of one sq cm
and a length of 1 cm.
porosity (effective): The ratio of the continuous void space
(through which water can move) to total volume, measured at
a point in a flow system.
radiometric age-dating: A method of absolute age determination
based on nuclear decay of natural elements. Calculating an
age, in years, for geologic materials by measuring the
presence of short-life radioactive elements, e.g.,
carbon-12/carbon-14, or by measuring the presence of a
long-life radioactive element and its decay product, e.g.,
potassium-40/argon-40.
recharge: The processes involved in the absorption and addition
of water to the zone of saturation.
reinjection well: A well in which fluid is introduced; often
used to dispose of waste liquid or possibly to replace
ground water removed from strata which might subside if the
water were permanently removed.
rift zone: A system of crustal fractures, usually producing a
valley or graben-like depression.
sag pond: A small body of water in a depression formed because
active or recent fault movement has impounded drainage.
salinity: Total quantity of dissolved salts in water, measured
by weight in parts per thousands or parts per million (ppm)
with the following qualifications: all carbonate has been
converted to oxide. bromide and iodide converted to chlor-
ide, and all organic matter completely oxidized.
sedimentary rock: Rock resulting from accumulation of sediment
or organic matter, e.g., shale, sandstone, conglomerate,
limestone.
335
-------
seismic survey: A geophysical prospecting technique that uti-
lizes a seismic source, such as a thumper or dynamite, and
sensitive detection instruments to record travel times.
Interpretation of this data allows the location of geologic
structures such as faults and thickness of lithologic
units.
sparker survey: A seismic survey in which an electrical dis-
charge in water is the energy source (also called exploding
wire).
solfataric activity: A late or decadent type of volcanic activ-
ity characterized by the emission of sulfurous gases from
the vent.
specific yield: The ratio of the volume of water a given mass
of saturated rock or soil will yield by gravity to the
volume of that mass.
Stiff diagram: A closed polygon representing the chemical char-
acteristics of a substance. Distinctions between substan-
ces can be easily observed by comparison of the different
polygonal shapes for each substance.
subduction zone: A region where one crustal block descends
beneath another by folding or faulting or both.
temperature gradient: See geothermal gradient.
transmissivity: In an aquifer, the rate at which water of the
prevailing viscosity is transmitted through a unit width
under a unit hydraulic gradient.
trilateration: A method of surveying where the lengths of the
three sides of a series of touching or overlapping trian-
gles are measured (usually by electronic methods) and the
angles are computed from the measured lengths.
underflow: The flow of water through the soil or a subsurface
stratum, or under a structure.
volcanic rock (extrusive): A rock formed from a magma at or
near the earth's surface. Usually fine-grained, sometimes
solidifying as ejected from a volcano, e.g. pumice, rhyo-
lite, andesite, basalt (lava flows).
water budget: See hydrologic budget.
336
-------
APPENDIX E
LIST OF ABBREVIATIONS
acre-ft
atm
BTU
°C
cal
Cal Tech
CDWR
cfs
cm
cu
d
ERDA
EPA
EPRI
OF
ft
ft/mi
g
gm
gpd
gpm
ha
ha-m
HFU
hr
in
J
KGRA
kg
kH
km
kW
kW.hr
LASL
1
-acre-feet
-atmosphere
-British Thermal Unit
-degrees Celsius (or Centigrade)
-calorie
-California Institute of Technology
-California Department of Water Resources
-cubic feet per second
-centimeter
•-cubic
•-day
•-U.S. Energy Research and Development
Administration
•-U.S. Environmental Protection Agency
•-Electric Power Research Institute
•-degrees Fahrenheit
-feet
•-feet per mile
•-acceleration of gravity
•-grams
•-gallons per day
•-gallons per minute
•-hectare
•-hectare-meter
—heat flow unit
•-hour
•-inch
•-joule
•-known geothermal resource area
•-kilogram
—transmissivity
•-kilometer
•-kilowatt
•-kilowatt-hour
•-Los Alamos Scientific Laboratory
—liter
337
-------
Ib
LBL
LLL
Ipd
1pm
Isd
m
M
ML
ma
md-ft
meq/1
mg
mg/1
mgal
m/km
mm
MM
msl
mv
MW
NCER
NOAA
ohm-m
OIT
oz
pci/l
PG&E
ppm
psi
psia
psig
SDG&E
sec
sq
TDS
U.C.B.
USER
USGS
USPHS
U.C.R.
(j mho/cm
P
4>ch
-pound
-Lawrence Berkeley Laboratory
-Lawrence Livermore Laboratory
—liter per day
•-liter per minute
•-land-surface datum
•-meter
•-earthquake magnitude determined from
instrumental data
•-earthquake magnitude, local scale
•-millidarcy
—millidarcy-feet
—milliequivalence per liter
•-milligram
•-milligram per liter
•-milligal
•-meters per kilometer
•-millimeter
•-Modified Mercalli Intensity
—mean sea level
•-millivolt
•-megawatt
•-National Center for Earthquake Research
•-National Oceanic and Atmospheric Administration
—ohm-meter
--Oregon Institute of Technology
—ounce
—picocurie per liter
—Pacific Gas and Electric Company
•-parts per million
—pounds per square inch
•-pounds per square inch absolute
—pounds per square inch gage
--San Diego Gas and Electric
•-second
—square
--total dissolved solids
--University of California, Berkeley
--U. S. Bureau of Reclamation
—U.S. Geological Survey
--U.S. Public Health Service
--University of California, Riverside
—micro mho per centimeter
—density
--storage capacity due to compressibility
338
* U.S. GOVERNMENT PRINTING OFFICE: 1979—786—265
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing}
. REPORT NO.
EPA-600/7-78-188
3. RECIPIENT'S ACCESSION NO.
TITLE AND SUBTITLE
GEOTHERMAL ENVIRONMENTAL IMPACT ASSESSMENT
Baseline Data for Four Geothermal Areas in the United
States
5. REPORT DATE
September 1978
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Subir Sanyal
Richard Weiss
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Geonomics, Inc.
3165 Adeline Avenue
Berkeley, CA 94703
10. PROGRAM ELEMENT NO.
1NE624
11. CONTRACT/GRANT NO.
68-03-2468
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency-Las Vegas, NV
Office Research and Development
Environmental Monitoring and Support Laboratory
Las Vegas, NV 89114
13. TYPE OF REPORT AND PERIOD COVERED
Interim
14. SPONSORING AGENCY CODE
EPA/600/07
is. SUPPLEMENTARY NOTES This ±8 the flrat ±n fl series of five reports prepared toward
developing a groundwater monitoring strategy in a geothermal resource area. Contact
Donald B. Gilmore. Project Officer. FTS 595-2969, x241, for additional information.
16. ABSTRACT
This report describes the existing data on climatology, hydrology, water chemistry,
seismicity, and subsidence in the Rio Grande Rift Zone, New Mexico; The Geysers,
California; the Klamath Falls, Oregon; and, with special emphasis, The Imperial Valley,
California.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
COSATl Field/Croup
Geothermal energy
Environmental studies
Geothermal groundwater
Monitoring
97P, R
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS {This Report)
TFWCT.ASSTFTRD
21. NO. OF PAGES
360 + 14 plates
20. SECURITY CLASS (This page)
UNCLASSIFIED
22. PRICE
EPA Form 2220-HR**- 4-77) PREVIOUS EDITION is OBSOLETE
------- |