MBMG 99
OCCURRENCE AND CHARACTERISTICS OF
GROUND WATER IN MONTANA
VOLUME 2
THE ROCKY MOUNTAIN REGION
by
Roger A. Noble, Robert N. Bergantino, Thomas W. Patton,
Brenda C. Sholes, Faith Daniel and Judeykay Schofield
1982
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PREFACE
R8
005S"
\A ^
This report on characteristics of aquifers in Montana is a two-volume
study; Volume I has been compiled for the Great Plains physiographic province
and Volume II for the Rocky Mountains physiographic province of Montana. The
division into two volumes was necessary in order to facilitate descriptions of
the various aquifers that occur in these two distinct topographic and structural
provinces. This report contains descriptions of thickness, potentiometric
surface, structural configuration and water-quality data for the major aquifers
within each province.
These two volumes contain a compilation of existing hydrogeologic informa-
tion for the State. Because statewide hydrogeologic investigations have only
recently begun in Montana, there are many data gaps, especially for the deeper
aquifers, and consequently some information is still conjectural. Demands on
Montana's ground water are expanding because of increasing energy development
and agricultural requirements (especially irrigation). For new developments,
ground water is the only alternative left, as most of Montana's surface waters
are already over-appropriated.
Montana is currently quantifying its water use and consumption through a
water-right adjudication program. This program is being implemented by the
Department of Natural Resources and Conservation through Senate Bill No. 76.
The completion date for the adjudication program is April 30, 1982; therefore,
quantitative statistics for Montana's ground-water use will not be available
until after this date. The ground-water use section is thus based on estimates
of current trends.
This study on aquifer characteristics in Montana was funded by the U.S.
Environmental Protection Agency through Contract No. GO-082-908-10, for the
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Underground Injection Control Program. The U.S. Congress enacted the Safe
Drinking Water Act (Public Law 93-523) for the purpose of protecting under-
ground sources of water from contamination caused by well injection. This
act mandated the U.S. Environmental Protection Agency to establish the Under-
ground Injection Control Program for the purpose of preventing underground
injections that endanger ground-water resources. The Montana Bureau of Mines
and Geology's role in the Underground Injection Control Program is to identify
and characterize the aquifers in the State of Montana.
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TABLE OF CONTENTS
CHAPTER PAGE
PREFACE ii
GENERAL STATEMENT 1
Purpose and Scope 1
Description of Montana 1
Previous Investigations 5
I. INTRODUCTION TO THE ROCKY MOUNTAINS REGION 6
Physiography 7
Topography 7
Surface Drainage 9
Climate 12
Cultural Geography 14
Population 14
Land Use and Ownership 19
Geology 20
Stratigraphy 20
Structure 22
II. HYDR0GE0L0GY BY AQUIFERS 26
Quaternary Unconsolidated Deposits 26
Tertiary Valley-Fill Sediments 29
The Tobacco Plains 32
Kalispell Valley 35
Swan Valley 38
Mission Valley 41
Little Bitterroot Valley 44
Missoula-Ninemile Valley . . 46
Blackfoot Valley 48
Prickley Pear Basin (Helena Valley) 51
Bitterroot Valley 57
Deer Lodge Valley 61
Townsend Valley 65
Three Forks Basin 69
Cold Spring Valley (North Boulder) 73
Little Whitetail and Jefferson Valleys 76
Melrose and Beaverhead Valleys 80
Madison Valley ..... 83
Emigrant Valley 86
Centennial Valley 89
Consolidated Sedimentary Rocks 93
Metamorphic and Igneous Rocks 95
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CHAPTER PAGE
III. GROUND-WATER USE 97
Agriculture 99
Municipal and Domestic 100
Industry 102
IV. WATER QUALITY 104
Data Sources 104
General Water Quality 105
Cenozoic Basin-Fill Deposits 107
Early Tertiary through Precambrian
Consolidated Sedimentary Rocks 110
Igneous and Metamorphic Rocks 110
V. SUMMARY 114
VI. REFERENCES CITED . 117
APPENDIX A: Well-numbering system 125
APPENDIX B: Glossary of terms 127
APPENDIX C: Montana Water Law 131
APPENDIX D: Printout of injection wells
(available upon request at current copying rates)
APPENDIX E: Printout of water quality analyses
(available upon request at current copying rates)
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LIST OF TABLES
TABLE PAGE
I-1 Drainage Area in Montana 3
II-2 River Basin Inflow and Outflow 11
II-3 Population of Counties and County Subdivisions .... 15-17
II-4 Well Use by County 98
II-5 Comparison of Selected Elements and Ions in Waters of
the Rocky Mountains Region, Montana, to Drinking
Water Quality Standards 106
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LIST OF FIGURES
FIGURE PAGE
II-l Major Drainage Basins 4
II-2 Mountain Ranges and Intermontane Valleys of the
Rocky Mountains Region 8
II-3 Mean Annual Runoff of Major Streams 10
II-4 County Census Subdivisions 18
II-5 Stratigraphic Column 23
II-6 Generalized tectonic map of the Rocky
Mountains region 24
II-7 Cenozoic Basins Evaluated 33
II-8 Isopach of Cenozoic fill in the Tobacco Plains ... 34
II-9. Isopach of Cenozoic fill in the Kalispell Valley . . 37
11-10 Isopach of Cenozoic fill in the Swan Valley 40
11-11 Isopach of Cenozoic fill in the Little Bitterroot
and Mission Valleys 42
11-12 Isopach of Cenozoic fill in the Missoula-
Ninemile Valley 47
11-13 Isopach of Cenozoic fill in the Blackfoot Valley . . 50
11-14 Isopach of Cenozoic fill in the Prickly Pear Basin . 53
11-15 Isopach of Cenozoic fill in the Bitterroot Valley . . 59
11-16 Isopach of Cenozoic fill in the Deer Lodge Valley . . 63
11-17 Isopach of Cenozoic fill in the Townsend Valley ... 66
11-18 Isopach of Cenozoic fill in the Three Forks Basin . . 71
11-19 Isopach of Cenozoic fill in the Cold Spring Valley . 75
11-20 Isopach of Cenozoic fill in the Little Whitetail and
Jefferson Valleys 78
11-21 Isopach of Cenozoic fill in the Melrose and
Beaverhead Valleys 81
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FIGURE PAGE
11-22 Isopach of Cenozoic fill in the Madison Valley .... 85
11-23 Isopach of Cenozoic fill in the Emigrant Valley ... 88
11-24 Isopach of Cenozoic fill in the Centennial Valley . . 91
11-25 Frequency of occurrence versus dissolved solids*for
waters from Quaternary and Early Tertiary unconsolidated
deposits, Rocky Mountains Region, Montana 108
11-26 Frequency of occurrence versus dissolved solids for
waters from Early Tertiary through Precambrian
consolidated rocks, Rocky Mountains Region, Montana . Ill
11-27 Frequency of occurrence versus dissolved solids for
waters from igneous and metamorphic rocks, Rocky
Mountains Region, Montana 113
11-28 Diagram showing well-numbering system 126
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LIST OF PLATES
Plate
DS 100.10 IV Quaternary and Late Tertiary Unconsolidated Sediments
DS 100.50 W Cenozoic Basin-Fill
TF 100.50 W Cenozoic Basin-Fill, W 1/2
DS Consolidated Sedimentary Rocks
DS Metamorphic and Igneous Rocks
Legend
TF - Thickness of Formation
DS - Dissolved Solids
211.11 - Formation Code
W - Western Half of Montana's 1:500,000 scale map
AVAILABLE AT CURRENT COPYING RATES
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GENERAL STATEMENT
PURPOSE AND SCOPE
This report was prepared by the Montana Bureau of Mines and Geology in
order for the State of Montana to comply with Federal requirements relating
to ;the Underground Injection Control Program. Existing hydrogeologic data
were used for the aquifer characterization maps and the descriptive narrative.
The aquifer characterization maps depict (1) the areal and subareal extent;
(2) surface configuration; (3) thickness; (4) potentiometric surface; and
(5) water chemistry (expressed as dissolved solids) for the major aquifers in
Montana. The narrative describes the lithology, general hydrogeologic parameters
and potential well yields for individual aquifers. The inventory of injection
wells was compiled from information obtained from the Montana Oil and Gas
Commission. The inventory provides a listing of injection wells with locations,
owners, affected aquifers and injection rates. The report also contains a
section delineating well use by county. While broad in scope, this report is
designed to meet the needs of Federal regulatory agencies responsible for
writing and implementing regulations for underground injection.
DESCRIPTION OF MONTANA
Montana, the third largest state of the 48 contiguous United States, is
vast and diverse. It has an area of 147,138 square miles and a population of
786,690 (U.S. Department of Commerce, 1980); the average population density is
5.4 people per square mile. Most Montanans live in the major cities that are
geographically dispersed throughout the state. These cities are supported by
the surrounding rural communities. Although Montana is sparsely populated, it
is rich in natural resources and is a prime producer of agricultural staples for
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the nation. Montana's abundant natural resources include fossil fuels, minerals,
timber and water. These resources, however, are either fully appropriated or
are being exploited rapidly.
In 1980, Montana's low-sulfur coal reserves were estimated to be in excess
of 120 billion tons (U.S. Bureau of Mines, 1980). These coal deposits of the
Fort Union Formation are easily accessible through strip-mining procedures and
supply a substantial part of needed energy for the nation. Total coal production
for 1980 was 29,905,627 tons (Cole and others, 1981), of which 90 percent was
exported to other states. Montana also has projected oil reserves of 248 trillion
barrels, an undetermined reserve of natural gas and unknown potential for uranium
resources (Montana Department of Natural Resources and Conservation, 1980).
Montana's mineral resources are of great economic importance to the State.
Montana ranks among the top five states in the production of antimony, silver,
copper, talc, vermiculite and bentonite (U.S. Department of the Interior, 1979).
In addition to these commodities, Montana has significant deposits of lead, zinc,
tungsten, chromium, manganese, nickel, titanium, vanadium, platinum-group metals,
molybdenum, arsenic, iron, antimony, thorium and other rare earths. Metallic
and nonmetallic exploration activity in the State is increasing every year.
Most of western Montana is heavily forested, and most of these forests lie
within designated State and national forests or parks. Timber harvesting occurs
on selected tracts within these forests and on privately owned land. The volume
of timber harvested in Montana from 1976 to present (1982) has decreased because
high mortgage rates have substantially reduced the number of buildings being
constructed.
Montana's water, both from ground-water reserves and surface-water flow, is
one of the State's most valuable resources because it is vital to agriculture,
mining and power production. More than 43 million acre-feet of water flow from
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the State each year; 65 percent of it originates in Montana (Montana Department
of Natural Resources and Conservation, 1976). Three major river basins—the
Columbia, Upper Missouri and Yellowstone—account for 97 percent of this flow.
Statistics concerning the drainage areas of the major river basins are presented
in Table II-l, with the major drainage basins displayed in Figure II-l.
TABLE II-l
DRAINAGE AREA IN MONTANA
River basin Area (sq. mi.) Percentage of Percentage of
Montana's area Montana's water
Columbia 25,152 17 59
Upper Missouri 82,352 56 17
Yellowstone 35,890 24 21
Little Missouri 3,428 2 1
St. Mary 648 1 2
147,470 100 100
Of the 15 million acres of cropland in production in the State, 12.5 million
acres are dryland and the remainder are irrigated. Montana's major water use is
the irrigation of these 2.5 million acres of cropland from both surface-water
and ground-water diversions. Agricultural demands, hydroelectric generating
facilities and instream-flow reservations have already claimed most of the
surface water. This surface-water demand has resulted in over-appropriation of
these waters, placing additional demands on ground-water resources. New sources
of potable ground water in certain areas are now limited.
For the purpose of this report, the State has been divided into the Rocky
Mountains region and the Great Plains region. Because geology, climate and
aquifer characteristics of the Great Plains region are significantly different
from those of the Rocky Mountains region, this natural physiographic division
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MAJOR DRAINAGE BASINS
FIGURE 11-1
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was used to facilitate the aquifer descriptions in this report. The line
separating the two divisions is not precisely the same as that used by geographers,
because it follows the eastern edge of rocks that were severely disturbed by the
Laramide orogeny rather than the actual mountain front, except where the two
coincide. The following is a compilation of data for each of the major aquifers
of the Rocky Mountains region.
PREVIOUS INVESTIGATIONS AND SOURCES OF INFORMATION
The collection of data for this report was made possible by the cooperation
of the U.S. Geological Survey, especially Richard D. Feltis and William R.
Hotchkiss, who furnished essential information on particular aquifer units.
Other data were compiled from oil-well logs of the Montana Oil and Gas Commission,
various Montana Bureau of Mines and Geology and U.S. Geological Survey publica-
tions, numerous theses and dissertations and unpublished information generated
from water-well logs and records.
Water-quality data in this report were obtained from Montana Bureau of Mines
and Geology files. Additional analyses were collected from the U.S. Geological
Survey.
Special gratitude is also expressed to Betty McManus for her patience and
clerical services in preparing this report.
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I. INTRODUCTION TO THE ROCKY MOUNTAINS REGION
The Rocky Mountains region of Montana is predominantly an area of rugged
mountain ranges and intervening valleys constituting the western one-third of
the State. This region extends from the eastern front of the Disturbed Belt
(a northwest-trending zone 25 miles wide where mountain-building forces deformed
the rocks, but did not result in a mountainous terrain) west to the Montana-
Idaho border. Latitude 49° north establishes the northern border and the
region's southern extent is delineated by Montana's borders with Idaho and
Wyoming. Linear mountain ranges form the Continental Divide separating this
region into two major drainage basins. The headwaters of the Columbia River
drain the northwestern portion of the region, whereas the tributaries of the
Missouri River drain the southeastern portion. Most of the State's large-scale
hydroelectric generating sites are located along these major rivers or their
tributaries. Although the rugged mountains are especially scenic features
within this region, the intermontane valleys or basins are important areas for
habitation, agriculture and ground-water usage.
The economy of the Rocky Mountains region is based on forest products,
mining, smelting, agriculture, governmental and educational activities and light
industry. Glacier and Yellowstone national parks and numerous designated wilder-
ness areas account for a substantial amount of the seasonal tourism. Oil and
gas exploration is increasing rapidly, with the current interest generated
along Montana's Overthrust Belt.
These economic operations have already placed a significant demand on the
region's water resources. As the population continues to grow, additional sources
of potable water will be needed. Because of the geologic nature of this region,
there exist only limited areas suitable for ground-water development. Volume II
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of this report is an examination of the occurrence and characteristics of ground
water in Montana's Rocky Mountains.
PHYSIOGRAPHY
Topography
The Rocky Mountains region of Montana covers approximately 54,750 square
miles of the northern Rocky Mountains physiographic province or roughly the
western one-third of Montana. The region consists of contrasting steep mountain
slopes and flat river valleys, which often contain some well-defined terraces
but relatively few foothills or prairie expanses. About three-fourths of the
region is occupied by a series of 40 or more individual mountain ranges that
are 25 to 75 miles long. In general, the mountain fronts rise abruptly from the
valley floors to peaks varying in altitude from 10,448 feet above sea level at
Mount Cleveland in northern Glacier National Park, to 12,799 feet above sea
level at the summit of Granite Peak in the Beartooth Mountains, northeast of
Yellowstone National Park. Floors of the intermontane valleys that separate the
mountain ranges lie at elevations ranging from 2,800 to 6,700 feet above sea
level (the Mission and Centennial valleys, respectively). These valleys, generally
containing a river, may be from a few miles to as much as 20 miles wide and 10 to
50 miles long. Elevations in the Rocky Mountains region range from 1,825 feet
above sea level, where the Kootenai River flows out of the State, to 12,799 feet
above sea level at Granite Peak. The locations and names of many of the mountain
ranges and intermontane valleys are shown in Figure II-2. Terraces or pediments
commonly adjoin the mountain fronts.
With some exceptions, the mountains of western Montana are dominantly com-
posed of metasedimentary rocks of Precambrian age; marine sandstones, shales and
carbonate rocks of Paleozoic and Mesozoic age; marine strata of Jurassic and
Cretaceous age; and andestitic volcanic rocks of Late Cretaceous and early
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Map of western TVIdntnri.i nnd julJ.nvnt arena, nhowlnir relations of the mountain ranges and Intermontnne valleyB (stippled):
1, I'un-fll Treneh ; U, Fl;ithe;i.l Valley; 3. KnlNpi'U Valley ; 4, Little lUttrroot Valley; 5, Camas i'rnlrlc Uasln; G, Mission Valley, 7, Jocko
Valley; 8, Ulnekfont Valley; ;i, Missoula Valley; 30, Ciiiiimr i'niirlc; 11, Nevnda Valley; 12, Bltterroot Valley; 13, Flint Creek Valley; 14,
Avon Valley; 35, Prlekly IYnr Vnlley; It), IMiilipshurp Valley; 17, Deer Lodge Valley; 38, Townsend Valley; 10, Smith Klver Valley;
20, Silver How Valley; lll, JUy ilolo Basin; 112, Vlpoiul i'urk; 23, Jefferson Valley; 24, Gallatin Valley; 25, Bcaverhend Valley; 20, Madison
Valley ; 27, C'entennlnl Vnlloj.
MOUNTAIN RANGES AND INTERMONTANE VALLEYS OF THE ROCKY MOUNTAINS REGION
FIGURE 11-2
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Tertiary ages. The Boulder batholith and its associated satellites in the
center of the region are composed principally of quartz monzonite of Cretaceous
age. The intermontane basins have been filled with Tertiary and Quaternary
sediments derived from the surrounding mountains.
Mountain glaciers extended over most of the region, leaving either various
glacial deposits or erosional features. These glaciers were responsible for
such erosional features as the jagged peaks and U-shaped valleys in Glacier
National Park and the Beartooth Mountains. They also produced the hummocky
kame and kettle topography around Ovando and the low hills (which are moraines)
in the Kalispell area. Many of the mountain lakes that dot mountain slopes and
valley plains mark the occurrence of glacial activity. Because of the geologic
diversity, topographic variability and structural complexity of this region,
isopach, potentiometric surface and structural configuration maps could be
produced only for specific aquifer units.
Surface drainage
Three major river systems in North America have their origins along the
Continental Divide in the Rocky Mountains region of Montana. These three river
systems are the Columbia, Missouri and Saskatchewan rivers. The common point
of juncture for these rivers is located at Triple Divide Peak in Glacier National
Park. Because of the westward deflection of the Continental Divide, most of the
drainage area for the Columbia River occupies the northwest portion of the
region, while the watershed of the Missouri River lies within the southeastern
portion of the region. Tributaries of the Saskatchewan River drain only a small
part of the region located in Glacier National Park. The mean annual runoff of
the major streams for the Rocky Mountains region is presented schematically in
Figure II-3, with a breakdown of drainage-basin inflow and outflow values shown
in Table II-2.
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MEAN ANNUAL RUNOFF OF MAJOR STREAMS
Width of stream line corresponds to top width of channel. Mean annual discharge, in
thousands of cubic feet per second, is represented by channel cross section.
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TABLE II-2
RIVER BASIN INFLOW AND OUTFLOW (IN ACRE-FEET)
Drainage
Inflow
Originating in Leaving Percentage originat-
the region the region ing in the region
Clark Fork
Kootenai
694,800 15,515,200
6,600,000 2,510,000
0 4,913,000
0 510,000
2,259,000 475,000
16,210,000
10,110,000
4,913,000
96
25
100
100
17
Missouri
Hudson Bay
Yellowstone
510,000
2,734,000
The Columbia River basin comprises all land in Montana west of the Contin-
ental Divide. This area has a substantial volume of surface water compared with
its total land area. While containing only 17 percent of the land mass of
Montana, this basin is the source of 59 percent of the State's total surface-
water outflow. The Clark Fork River and the Kootenai River are the two major
tributaries of the basin. The Clark Fork River heads in Silver Bow basin south
of Butte, originating as Silver Bow Creek. The Clark Fork River joins other
major tributaries—the Bitterroot, Blackfoot and Flathead rivers—at their
confluences, to become the Pend Oreille River in Idaho. A small area in the
northwestern corner of the region adds to the watershed of the Kootenai River.
The Clark Fork has an average annual flow of 16,210,000 acre-feet near Cabinet,
Idaho, at the Montana-Idaho border, as compared to the Kootenai's average out-
flow of 10,110,000 acre-feet per year at Leonia, Idaho. Major tributaries of
the Kootenai River are the Yaak and Fischeries rivers.
The Columbia River basin has almost 12 million acre-feet of storage. Lake
Koocanusa is the largest reservoir, with a storage capacity of 5,850,000 acre-
feet. Hungry Horse reservoir and Flathead Lake are the other major storage sites,
with capacities of 3,468,000 and 1,791,000 acre-feet of total storage, respectively.
The Missouri River basin drains the eastern slopes of the Continental Divide.
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At the eastern border of the Rocky Mountains region, the Missouri River has a
drainage area slightly smaller than the Columbia River, yet has about one-third
of the Columbia River's average discharge. The Missouri River begins at the
confluence of the Jefferson, Madison and Gallatin rivers below Three Forks.
Canyon Ferry, with a total storage capacity of 2,051,000 acre-feet, on the main
stream of the Missouri River, is the largest reservoir in this portion of the
region.
The Hudson Bay drainage in the Rocky Mountains region consists primarily
of the St. Mary River and its tributaries draining the northeast corner of
Glacier National Park. The river flows northward to join the Saskatchewan
River in Canada.
A portion of the Yellowstone River's watershed also arises in the south-
eastern corner of the Rocky Mountains region. Only a few hundred cubic feet
per second are produced from its small watershed.
Climate
Because western Montana has a great amount of topographic variation, it
also has a great variety of climate. This climatic diversity is such that most
small-scale climate maps show western Montana as having merely a "highland"
climate. More detailed climate maps using the Ko'ppen classification system
would show that the intermontane valleys have a "steppe" climate (BSk); that
the mountains would have various microthermal or "snow forest" climates such as
Dbf, Dbs, Dcf and Dcs; and that the summits of the higher mountains would have
"tundra" climates (ET). The Thornwaite climate classification shows the climate
of the intermontane valleys and some of the mountains in southwestern Montana
to be "subhumid, microthermal, precipitation deficient in all seasons" (cc'd).
The mountains of northwestern Montana and those in the southeastern part of the
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Rocky Mountains region are shown to have the following climates: subhumid,
microthermal, precipitation adequate in all seasons (cc'r); humid, microthermal,
precipitation adequate in all seasons (Bc'r); and taiga (d'). Not shown on the
Thornwaite map, but present on many of the higher peaks, would be "tundra" (ET).
That a map has yet to be prepared for Montana accurately showing the extent of
these climatic provinces is not surprising, considering that many other factors
besides topography are important in determining mountain climates. Some of
these other factors are rainshadow effect, direction and strength of the prevail-
ing wind, slope angle, air drainage, latitude, longitude, valley width and valley
orientation. Long-term temperature and precipitation records are generally
available only for major cities, most of which are located in intermontane valleys.
Supplemental climate data from snow-survey sites on the mountains are now adding
greatly to the understanding and quantification of the climate of western Montana.
Climate records show that the valleys of extreme west-central Montana have
the warmest July temperatures. July average maximum temperatures of 88°F occur
at Thompson Falls along the Clark Fork River. Warm July temperatures in this
part of the State result from long, clear days, lower altitudes and reflective
heating from the north valley slopes (south-facing slopes). The July average
maximum in Butte is 80°F, and at West Yellowstone it is 75°F. Maximum shade
temperatures on mountain summits in July often average 65°F or less. Average
minimum temperatures in July are as low as 40°F in northwestern Montana and the
high valleys of southwestern Montana. Because of the low humidity, radiative
cooling begins as soon as the sun sets. January average minimum temperatures
are generally as much as 15°F warmer than those in northwestern Montana, and
usually keep the temperature more moderate compared to the Great Plains region
where Arctic air masses are dominant in winter. Extreme low temperatures occur
in western Montana when Arctic air masses spill across the mountain barriers.
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Average annual precipitation amounts in western Montana range from less
than 10 inches in the intermontane basins of southwestern Montana to more than
100 inches in Glacier National Park. Precipitation amounts generally increase
with altitude except where severe rainshadow conditions exist on the lee side
of the mountains. Monthly weather records show that two precipitation maxima
occur in western Montana—one in midwinter and the other in late May to early
June. Average annual snowfall amounts range from 25 inches in the area near
Townsend (along Canyon Ferry reservoir) to more than 1,000 inches on the summits
in Glacier National Park. The average snowfall in most of the major cities is
between 40 and 90 inches. The snowpack on the mountains of western Montana
serves as a great storage reservoir for the many streams that have their head-
waters in the area. Melting snows release water slowly to these streams, keeping
them flowing long after the late spring rains have ceased.
CULTURAL GEOGRAPHY
Population
The Rocky Mountains region encompasses roughly one-third of Montana's
land area, yet one-half of the State's population inhabits the region. According
to 1980 census figures, 393,625 persons are living in the region, yielding a
population density of 7.12 persons per square mile. Because the region is pre-
dominantly comprised of rugged mountain ranges, approximately 90 percent of the
people live in the intervening valleys. Major cities exceeding 10,000 people
account for 37 percent of the region's population. The 1980 census defined a
city as an incorporated place, and according to this classification the major
cities in order of their size are Butte, Missoula, Helena, Bozeman, Anaconda and
Kalispell. The population distribution for the Rocky Mountains region is sum-
marized in Table II-3, with the county census subdivisions represented in Figure II-4.
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TABLE II-3
POPULATION OF COUNTIES AND COUNTY SUBDIVISIONS
OF THE ROCKY MOUNTAINS REGION, MONTANA
County/County Subdivision 1980 1970 % Change
Beaverhead County 8,186 8,187
Big Hole Basin Division 740
Clark Canyon-Horse Prairie Division 426
Dillon Division 6,567
Lima-Centennial Valley Division 453
Broadwater County 3,267 2,526 29.3
Townsend East Division 2,522 2,016 25.1
Townsend West Division 745 510 46.1
Cascade County 80,696 81,804 - 1.4
Sun River Valley Division 3,258 2,558 27.4
Deer Lodge County 12,518 15,652 -20.0
Anaconda Division 10,403
Deer Lodge Valley Division 2,115
Flathead County 51,966 39,460 31.7
Bad Rock-Columbia Heights
Division 2,793
Columbia Falls Division 6,574
Creston-Bigfork Division h,114 2,315 77.7
Glacier Division 105 153 -31.4
Kalispell Division 22,860
Kalispell Northwest Division 1,939
Kalispell Southwest Division 2,700
Lower Valley-Somers Division 1,183
South Fork Division 2,000
Whitefish Division 7,698
Gallatin County 42,865 32,505 31.9
Belgrade Division 5,884
Bozeman Division 28,604
Gallatin Gateway Division 1,949
Manhattan Division 3,057 2,448 24.9
Three Forks Division 1,997 1,839 8.6
West Yellowstone Division 1,374 1,099 25.0
Glacier County 10,628 10,783 - 1.4
Blackfeet Division 6,039
Glacier National Park Division 49
Granite County 2,700 2,737 - 1.4
Drummond Division 1,092 1,141 - 4.3
Philipsburg Division 1,608 1,596 0.8
Jefferson County 7,029 5,238 34.2
Boulder Division 4,518 3,350 34.9
Whitehall Division 2,511 1,888 33.0
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TABLE II-3 (Continued)
POPULATION OF COUNTIES AND COUNTY SUBDIVISIONS
OF THE ROCKY MOUNTAINS REGION, MONTANA
County/County Subdivision 1980 1970 % Change
Lake County
19,056
14,445
31.9
Big Fork-Swan Division
1,998
Charlo Division
1,242
1,111
11.8
Poison Division
7,492
Ronan Division
4,875
St. Ignatius Division
3,449
2,797
23.3
Lewis and Clark County
43,039
33,281
29.3
Augusta Division
847
854
- 0.8
Helena Division
38,853
Lincoln Division
2,234
Wolf Creek Division
1,105
Lincoln County
17,752
18,063
- 1.7
Eureka Division
3,727
3,558
4.7
Libby Division
10,960
12,045
- 9.0
Troy Division
3,065
2,460
24.6
Madison County
5,448
5,014
8.7
Harrison Division
762
800
- 4.8
Madison Valley Division
1,466
1,179
24.3
Sheridan Division
1,525
1,337
14.1
Twin Bridges Division
1,387
1,437
- 3.5
Virginia City Division
308
261
18.0
Meagher County
2,154
2,122
1.5
Martinsdale-Ringling Division
377
White Sulphur Springs Division
1,777
Mineral County
3,675
2,958
24.2
Alberton Division
587
600
- 2.2
Superior Division
2,126
1,580
34.6
West End Division
962
778
23.7
Missoula County
76,016
58,263
30.5
Frenchtown-Enaro Division
3,665
1,547
136.9
Lolo Division
4,871
1,747
178.8
Missoula Division
65,476
Seeley Lalce-Blackfoot Valley
Division
2,004
1,201
66.9
Park County
12,660
11,197
13.1
Gardiner-Cooke Division
860
845
1.8
Shields Valley Division
1,471
Upper Yellowstone Valley
Division
10,329
- 16 -
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TABLE II-3 (Continued)
POPULATION OF COUNTIES AND COUNTY SUBDIVISIONS
OF THE ROCKY MOUNTAINS REGION, MONTANA
County/County Subdivision 1980 1970 % Change
Pondera County
Blackfeet West Division
Powell County
Avon-Elliston Division
Deer Lodge Division
Helmville Division
Ravalli County
Darby Division
Hamilton Division
Stevensville Division
Sula-Edwards Division
Victor Division
Sanders County
Flathead Division
Plains Division
Thompson Falls-West End Division
Silver Bow County
Butte'Division
Silver Bow Northwest Division
Silver Bow South Division
Toole County
South Toole Division
Sunburst Division
Yellowstone County
Yellowstone National Park Division
6,731 6,611 1.8
473
6,958 6,660 4.5
1,002 1,018 - 1.6
5,473
483
22,493 14,409 56.1
1,718
11,467
6,516
950
1,842
8,675 7,093 22.3
1,887 1,907 - 1.0
2,553 1,938 31.7
4,235 3,248 30.4
38,092 41,981 - 9.3
36,817
491
784
5,559 5,839 - 4.8
3,932
1,627 1,904 -14.5
108,035 87,367 23.7
275 64 329.7
- 17 -
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CANADA
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COUNTY
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INCORPORATED OR UNINCORPORATED
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WASHINGTON COUNTY
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COUNTY CENSUS SUBDIVISIONS
FIGURE 11-4
- 18 -
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Butte is the largest incorporated place within the region, attributing its
size to a prosperous copper-mining industry of the past. Butte typifies a boom
town, which had a population of over 100,000 around the turn of the century and
has now receded to 35 percent of that early-day size. This trend in population
decline roughly parallels the decline in employment in the copper industry.
According to Rand-McNally's 1977 Atlas, Butte's basic trading area includes
91,300 people.
Missoula and Helena are, respectively, the second and third largest incor-
porated places of the region; however, Missoula's metropolitan area now exceeds
80,000 people. Missoula initially owed its growth to the timber industry, once
being the home of five major lumber mills for the area. The population of this
city, however, has increased 13.2 percent since 1970 as small industry and the
University of Montana expand. Serving in excess of 118,000 residents, Missoula
has the largest basic trading area in the Rocky Mountains. Helena is the capital
of Montana and is dominantly supported by government employees. Its population,
though, continues on an upward trend.
The overall population of the Rocky Mountains region has increased 16.6
percent since the 1970 census, yet particular counties deviate greatly from this
trend. An example of this is the 56.1 percent increase of Ravalli County, which
is due to an influx of people throughout the Bitterroot Valley. The other extreme
is the 9.3 percent decline of Silver Bow County owing to a depressed copper-
mining industry.
Land use and ownership
The primary land use in the Rocky Mountains region is forest. Roughly
one-half of this region is considered forest land, of which 60 percent is class-
ified as commercial forest. However, timber harvesting has been reduced owing
to the associated decline in construction. Most of the forest land in the region
- 19 -
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is under Federal control and managed by the U.S. Forest Service or Bureau of
Land Management. The remainder is either under State jurisdiction or private
ownership.
The next largest land use is rangeland for livestock grazing. Rangeland
consists of grazeable forest land, tame pasture and native rangeland. These
lands are vital not only for cattle and sheep production, but are grazed also
by big game and other wildlife. Approximately 35 percent of total land area of
the Rocky Mountains region is used for rangeland and is owned dominantly by
private individuals or corporations.
Agriculture cropland accounts for approximately 8 percent of land use of
the region. This land use includes irrigated and non-irrigated cropland and
irrigated and non-irrigated pasture land. With agriculture being ranch oriented,
hay production is the major use of cropland acreage. Most of this acreage occurs
along the flat and gentle slopes of the river bottom land and terraces and along
the foothills of the mountains. Nearly all cropland is privately owned.
The remainder of land use for the Rocky Mountains region spans from
recreation and wildlife refuges to community facilities. Indian lands, national
parks and wilderness areas comprise most of the land acreage, while municipal-
ities and subdivisions are increasing rapidly. For the most part, the former
areas are federally owned, and the latter are under private ownership.
GEOLOGY
Stratigraphy
A composite stratigraphic section, ranging in age from Precambrian to
Holocene, is present in the Rocky Mountains region of Montana. These formations
constitute many of the rugged mountains of western Montana.
- 20 -
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The oldest rocks are the gneisses arid schists of the early Precambrian
Era (1.7 billion years old) of southwestern Montana. Most of the bedrock
formations exposed are the Precambrian metasediments of the Belt Series, which
cover much of the northern half of the region. These formations were mainly
shelf and marginal shelf sediments deposited in a geosyncline. They were then
altered by burial metamorphism to argillites and quartzites of their present
configuration. Commonly they exist as assemblages tens of thousands of feet
thick.
Seas again spread over the area during the Paleozoic Era, depositing the
shales and limestones of the Cambrian period. A temporary hiatus occurred during
the Ordovician through Middle Devonian periods, leaving a stratigraphic gap.
Widespread shallow seas then deposited carbonates from Late Devonian through
Mississippian time. Fractures in the Madison limestone of this period serve for
both recharge and sources of ground water in bedrock aquifers. Tectonic activity
accompanied the invasion of Pennsylvanian and Permian seas, producing the clastic
sediments of those periods. During Jurassic and Cretaceous times, seas again
moved into the region, leaving alternating transgressive and regressive sedimen-
tary sequences. These Paleozoic and Mesozoic formations exist in large bedrock
assemblages of shales, carbonates and sandstones, with the carbonates and sand-
stones being the primary sources of ground water.
Tertiary and Quaternary deposits of the Cenozoic Era mainly occur in the
intermontane valleys. For the most part, they are fluvial sediments derived from
the surrounding mountains. These unconsolidated sediments serve as a primary
ground-water source for most municipalities throughout the region. Mountain
valley glaciers covered much of western Montana during the Pleistocene Epoch.
The glaciers produced till and outwash deposits, which now form a veneer over
some valleys and mountain fronts and are sources of nominal amounts of ground
- 21 -
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water. Figure II-5 portrays the generalized stratigraphic sections for the
Rocky Mountains region.
Structure
The structural geology of the Rocky Mountains region is extremely complex
and variable throughout the area. Deformation occurred in several phases, begin-
ning in Late Cretaceous and extending to the end of the Paleocene. This deforma-
tion through folding, faulting and igneous activity has produced the mountain
ranges and valleys of western Montana. Particular ranges are oriented so that
they can be categorized into distinct geologic provinces.
Through a combination of geographic, structural and lithologic character-
istics, the region can be divided into three separate provinces. The northern-
most is the Belt province, which lies north of the Montana Lineament and extends
to the eastward margin of the Disturbed Belt. The area is characterized by
northwest-southeast-trending mountain ranges and accompanying high-angle, normal
faults. Precambrian Belt sediments outcrop across most of the area, while im-
bricate thrusts of Paleozoic and Mesozoic age comprise the Disturbed Belt.
Northwest-southeast-trending intermontane valleys filled with Cenozoic sediments
are also characteristic of the region. Lying south of the Montana Lineament and
north of the Basement Province is the Batholithic Province. This area contains
numerous Late Cretaceous and Tertiary igneous plutons, the best of which is the
Boulder batholith. Extrusive igneous rocks and irregularly shaped basins are
also abundant in this province. The Basement Province is the third province of
the region and is typified by its pre-Belt metamorphic assemblages. Northeast-
striking, high-angle faults in this area demonstrate the regional stress orienta-
tion active during the Laramide orogeny. Figure II-6 is a generalized tectonic
map showing these provinces for the Rocky Mountains region. Because the Rocky
- 22 -
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PERIOD
NORTH AMtfiKAH
MAMMAL ACS.
Figure 11-5 Stratigraphic column
- 23 -
-------
ro
•fN
HIGH ANGLC FAULTS
REVERSE OR THRUST FAUI-T^j ^ ^ ^
_JSr— MAJOR FOLD TRENDS
IGNEOUS INTRUSIVES
PROVINCE BOUNDARIES
MODIFIED FROM McMANNIS (1965)
YELLOWSTONE PARK
Generalized tectonic map of the Rocky Mountains region
Figure 11—6
-------
Mountains region is so structurally complex and active, it has been placed in
seismic risk zones of 2 and 3, moderate and major damage, respectively. Fault
lines usually serve as good water conduits and are occasionally tapped by wells.
Since deformation of individual formations beyond meaningful aquifer units
has occurred, four separate hydrologic units were identified for the Rocky
Mountains region. The four units defined for the presentation are (1) consoli-
dated sedimentary rocks—of all geologic ages; (2) Tertiary basin-fill deposits;
and (3) Quaternary unconsolidated sediments. Also, because of the structural
complexity of the region, no attempt was made to construct isopach or structure
contour maps with the exception of Cenozoic basin fill. Thicknesses of Cenozoic
basins were determined largely by interpretation of gravity data because of the
paucity of drill holes penetrating bedrock.
- 25 -
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II. HYDROGEOLOGY BY AQUIFERS
QUATERNARY UNCONSOLIDATED SEDIMENTS
Alluvium and glacial deposits comprise most of the Quaternary unconsolidated
aquifers, while other aquifers consist of colluvium and terrace gravel deposits.
All of these sediments are composed of unconsolidated gravels, sands, silts and
clays. Water availability from these deposits is widely variable and is depen-
dent upon the characteristics of the deposits.
Alluvial aquifers border present-day streams. These aquifers consist of a
variety of sedimentary sequences such as point bars of cross-bedded sands, gravel
lag deposits and finer-grained materials that form natural levees. The stream
is hydraulically connected to the alluvial aquifer, and there exists a definite
surface water-ground water interaction between them. For the most part, the
alluvium is a water-table aquifer, and ground-water movement normally follows
the topography in a downstream direction. An alluvial aquifer may also be a
confined or semiconfined system when clays form impermeable boundaries. Because
these aquifers adjoin a stream, they tend to have an elongated surface expression.
The increase in thickness and areal extent of an alluvial aquifer is usually
directly proportional to the stream's average annual discharge except where the
stream is constricted by resistant geologic formations.
The transmissivity and storativity of alluvial aquifers may vary consid-
erably from one location to the next, reflecting depositional variations in the
sediments themselves. However, an alluvial aquifer imparts a stronger horizontal
than vertical conductivity. Transmissivity and storativity values for an alluvial
aquifer are generally large, and such aquifers will produce yields of up to 1,500
gallons per minute (gpm). Recharge to alluvial aquifers in western Montana is
primarily from rainfall and snow-melt water, while additional amounts result from
- 26 -
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irrigation return flows and influent streams. Wells, effluent streams, evapo-
transpiration and leakage to underlying aquifers are the primary means of dis-
charge. The ground water in alluvial aquifers has a dissolved solids content
of around 350 milligrams per liter (mg/L) and is highly sought for domestic and
municipal use. Alluvial aquifers are one of the most important sources of ground
water in the Rocky Mountains region.
Glacial aquifers are the other primary source of ground water among uncon-
solidated sediments. These Pleistocene deposits occur as till and glaciofluvial
or lacustrine sediments that mantle bedrock and Tertiary sediments. They range
from a few feet to hundreds of feet thick, depending upon their location and
mode of deposition.
Because glacial till is a heterogeneous mixture of boulders, gravel and
sand within a matrix of silt and clay, it has a relatively low hydraulic conduc-
tivity. Well yields from till are usually small, and discharges range from 5
to 20 gpm. Near rock outcrops, the till contains an abundance of boulders and
gravels and progressively becomes more clay-rich where it is farther from the
outcrops. When running water reworks the till, it sorts the glacial materials,
removing the finer-grained deposits. The remaining deposits often resemble
alluvium, but because of their mode of formation, they are termed glaciofluvial
deposits. These deposits are paleodrainages that were once Pleistocene river
channels. This type of deposit covers a substantial area near Kalispell.
Although glaciofluvial deposits may commonly be masked by a blanket of till
deposited by an advance of glacial ice, their linear form generally is surficially
expressed on aerial photographs. Well yields increase measurably in glacio-
fluvial deposits because fluvial action has removed most of the silt and clay,
increasing porosity and permeability to produce a highly conductive aquifer.
Wells and ground-water pits that have been completed in glaciofluvial deposits
- 27 -
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have yielded as much as 1,500 gpm with only a few feet of drawdown throughout
the irrigation season.
In areas where glacial drift is thick and stratified, a number of aquifers
can be found. Some areas have a deep artesian aquifer, a shallow artesian
aquifer and a perched aquifer. Wells developed in the deep artesian aquifer
have been found to be capable of yielding 3,500 gpm with almost no drawdown.
Yields for the shallow and perched aquifers are primarily used for domestic
wells, but yields of 500 gpm in some areas are possible.
The glaciolacustrine sediments are a less common type of aquifer and are
composed primarily of silt- and clay-sized materials that were deposited as
glacial lake sediments. Well yields from these aquifers are exceedingly small.
They are usually passed over for a better source owing to their aquitard
characteristics.
Depending on location throughout the Rocky Mountains region, there may
exist only a single aquifer or a combination of aquifers contingent upon the
extent of glaciation. Recharge to the deep aquifers is dominantly from pre-
cipitation infiltrating along the mountain fronts, whereas the shallow systems
receive direct infiltration. Minot sources of recharge are irrigation return
flow, aquifer leakage and stream and lake seepage. Wells and springs account
for most of the discharge, with the remainder from evapotranspiration and
effluent streams.
Water quality of glacial aquifers is generally very good, having an average
dissolved-solids concentration of 450 mg/L. This figure often varies though as
a factor of depth and locality. The glacial deposits are the most important
source of ground water in the northern half of the Rocky Mountains region be-
cause of their quality and quantity.
- 28 -
-------
A number of wells are drilled in colluvium and terrace gravel deposits,
which are geomorphically expressed as fans and benches, respectively. Both
colluvial fans and terrace benches are juxtaposed next to mountain fronts and
are usually incised by ephemeral streams. Coarser-grained materials, such as
cobbles and gravels, lie nearer to the mountain front, while finer-grained
materials, such as sand, silt and clay, increase toward the center of the valley.
These sediments interfinger laterally and show a marked decrease in hydraulic
conductivity with distance from the mountain front until the valley stream is
reached. Well yields of up to 200 gpm have been recorded, but values of 20 to
50 gpm are more representative of average well yields. Water from these wells
is of good quality and is primarily used for domestic and stockwater purposes.
Recharge is dominantly from precipitation; springs and wells are the major medium
of discharge. Colluvium and terrace gravels serve as a reliable source for
small-capacity wells.
TERTIARY VALLEY-FILL SEDIMENTS
Tertiary-age sediments comprise most of the basin-fill deposits found in
western Montana's intermontane valleys. Originally, these terrestrial deposits
were referred to collectively as the Bozeman Group (Robinson, 1963). Recent
investigations by Kuenzi, Fields, Richard, Petkowich and others have divided the
Bozeman Group into various formations dependent upon lithologic and paleontologic
relationships. The Tertiary deposits in the basins of southwestern Montana are
composed of a distinct upper and a lower sequence of sediments. Although two
separate formations are recognized, it appears that detritus from the surrounding
mountains infilled the basins under similar climatic conditions, but different
drainage systems account for the varied lithologies. Volcanic ash seems
ubiquitous to both formations, and according to Kuenzi (1966), the composition
- 29 -
-------
of the volcanic glass and clay mineral suite ^cannot be used to distinguish
rock units or geologic age. Correlating the different formations from one
basin to the next is a recognized problem that has yet to be unraveled.
Unconformably underlying the Quaternary unconsolidated sediments is the
Sixmile Creek Formation and its equivalents of middle Miocene to Pliocene age.
The formation is topographically expressed as pedimented slopes that dip toward
the center of the valley. This formation is lithologically characterized by
coarse-grained sediments of higher energy environments such as perennial and
ephemeral streams. Typical lithologies include interbedded sandstones, channel
conglomerates, tuffs and siltstones. Because of the coarse-grained nature of
this formation, it represents a viable source for ground water. Wells penetrat-
ing this upper formation usually have yields of 5 to 35 gpm, depending upon
locations. Values for transmissivity and storativity for these sediments are
generally unknown, because only a few wells have been aquifer tested. Wells
completed in Tertiary sediments are drilled to varying depths but usually extend
from 100 to 300 feet below the ground surface. The water quality of the Sixmile
Creek Formation is fair to good and is suitable for domestic and stockwatering
purposes. Values for dissolved solids range from 83 mg/L in the Bitterroot
Valley, to 1,268 mg/L in the Deer Lodge Valley, with an average of about 500 mg/L.
The lower sedimentary sequence, the Renova Formation, unconformably under-
lies the Sixmile Creek Formation. The Renova ranges from late Eocene to early
Miocene age. This formation is comprised mainly of finer-grained sediments
indicative of restricted depositional environments such as ponds, lakes and flood
plains. Common lithologies found in the Renova Formation include alternating
layers of thin-bedded claystones, siltstones, poorly sorted mudstones and
tuffaceous deposits. Although these sediments probably contain a large amount
of ground water in storage, the nature of the clays prevents it from being
- 30 -
-------
withdrawn. Because this formation generally occurs at substantial depths in
the basins and does not readily produce ground water, it is seldom used as an
aquifer.
Recharge to Tertiary valley-fill sediments is derived from interaquifer
seepage from the overlying stream alluvium and alluvial fans, infiltration from
precipitation and irrigation return flows. Wells, springs, seeps and evapo-
transpiration account for most of the discharge from these sediments.
The thickness of the Tertiary sediments and the configuration of the base-
ment bedrock of Montana's intermontane valleys have been largely unknown variables.
In order to compile an aquifer-thickness map for the UIC project, the valleys were
computer modeled where sufficient gravity surveys have been completed. The
modeling program integrates Bouguer gravity values versus depth, using a pre-
determined value for the difference between bedrock density and valley-fill
density. Because very little is actually known about the degree of compaction
or alteration of deeper sediments, a single density contrast value is used for
the total depth of the sediments.
Inasmuch as this is a two-dimensional program, numerous gravity profiles
across a valley were needed to construct isopach contours. The result is an
interpretation of the total thickness of the Cenozoic sediments within the inter-
montane basin. Seismic investigations and scant drill-hole data were utilized
to add credence to the predicted bedrock depths.
Many hours were spent obtaining the extensive information necessary to
evaluate the basins. Additional computer time was also logged to generate
supplementary data. Nevertheless, inaccuracies exist, and revisions will be
made as new information becomes available. It should be noted that many of the
previous estimates of Cenozoic valley-fill thickness appear to be on the con-
servative side compared with projections in this report.
- 31 -
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The following is a basin-by-basin analysis of the Cenozoic valley-fill
thickness of selected intermontane valleys in western Montana and a summary
of the ground-water occurrence in these valleys. Figure 11-7 is a schematic
diagram showing the locations of the intermontane valleys of western Montana
and those which were evaluated.
The Tobacco Plains
The Tobacco Plains valley is located in the extreme northwest corner of
the State. The valley lies within the Rocky Mountain Trench and is bordered by
major longitudinal gravity faults (Coffin and others, 1971). The Whitefish
Mountain range forms the eastern wall of the valley, whereas the Salish Moun-
tains and Purcell Mountains delineate its western border. The northern limit
of the basin is the international border, although the valley extends into Canada.
Rocks outcropping along the valley margin belong, for the most part, to the
Precambrian Siyeh Formation with others being lower Piegan and Ravalli Group
rocks. These rocks are inferred to underlie the Cenozoic fill in the valley.
The types of sediments deposited in the valley during the Tertiary period are
unknown, because they are not exposed and deep-test-hole logs are not available.
Along the international border, gravity data indicate that the valley fill is
slightly more than 3,000 feet thick at the center of the valley (Figure II-8).
Glacial deposits of unknown thickness overlie the Tertiary sediments. Three
distinct periods of glaciation occurred in the valley, with the last glacial
advance and retreat largely obscuring or eradicating earlier deposits (Coffin
and others, 1971). This last glacial epoch is responsible for the formation
of the major aquifers in the valley.
The hydrogeology of the Tobacco Plains is rather complex because of its
- 32 -
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- 33 -
-------
Isopach Interval: 1000 ft.
Map Scale: 1:500,000
Refer to basin no. 3
Isopach of Cenozoic fill in the Tobacco Plains
Figure II-8
- 34 -
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glacial origin. The oldest aquifer of the area is the Precambrian metasedimen-
tary rocks. Fractures in these rocks yield from 1 to 10 gpm of water to wells
and springs. The ground-water availability of Tertiary sediments is unknown
because of their undetermined presence. Glaciofluvial deposits are the most
important source of ground water in the basin. These deposits are composed of
moderately well sorted to well sorted clays, sands and gravels. The thickness
of these glaciofluvial deposits varies from one locale to the next, and they are
generally capable of 10 to 50 gpm sustained yields. Alluvium bordering the
Kootenai River is the other primary source of ground water. Wells tapping the
alluvium have yields ranging from 5 to 25 gpm, sufficient for domestic and
stockwater use.
Overall, the ground water of the basin is of good chemical quality. Though
the water is somewhat hard, it is suitable for domestic, stockwater and irriga-
tion uses. Dissolved solids have an average value of around 300 mg/L, and the
major constituents are calcium, magnesium, sodium and bicarbonate. Precipitation
accounts for most of the recharge to the aquifer system, with a minor amount con-
tributed by irrigation runoff. Discharge occurs principally from wells, springs
and evapotranspiration. Ground water also maintains a base flow for most of the
streams in the drainage basin. The Tobacco Plains basin is sparsely populated
and to date has not placed substantial demands on the ground-water system.
Kalispell Valley
The Kalispell valley lies in the southern portion of the Rocky Mountain
trench. The valley is bounded on the west by the Kalispell fault, which is
located along the east base of the Salish Mountains. The Swan-Whitefish fault
forms its eastern border. The north shore of Flathead Lake is considered the
southern limit of the valley, while the northern end progressively pinches out
- 35 -
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at Whitefish Lake. The Structural framework of the valley is apparently con-
trolled by a series of north-northwest-trending subparallel faults and two
associated cross faults (Figure II-9). The area north of the Creston fault is a
graben. These structural features serve to spatially render the valley an ellip-
tical bowl. Isopach contours show that the Cenozoic fill has a maximum thickness
of 4,000 feet near LaSalle, Montana. South of the Creston fault, gravity data
indicate that the area around Big Fork is an upthrown block bounded by two smaller
grabens. Both of these smaller valleys contain approximately 2,000 feet of valley
fill (Figure II-9). According to Konizeski, 1968, unconsolidated to semiconsoli-
dated Tertiary rocks occur in many northern Rocky Mountain intermontane basins
of comparable size, but none is exposed in the Kalispell valley. It is assumed
that Tertiary fill overlies the same Precambrian bedrock that crops out along
the valley margins. The fill is probably comprised of Miocene and Oligocene
gravels, sands, silts and clays. An unknown thickness of Pleistocene glacial
deposits of Wisconsin age overlie the Tertiary sediments. The north-central and
western parts of the valley are mostly morainal deposits composed of till, whereas
the south end of the valley contains well-bedded clays and silts of glaciolacus-
trine origin. In some locales, dune sand or glaciofluvial deposits cover the
area. Holocene alluvium overlies the glacial sediments along valley bottoms
and borders the major streams. Point bars and flood-plain deposits characterize
alluvial deposits and generally are only a few feet thick. The hydrogeology of
the Kalispell valley is exceeding complex because of the heterogeneity of the
glacial sediments. The discontinuity and interfingering of these deposits make
it virtually impossible to predict aquifer parameters. Konizeski and others (1968)
delineated three distinct aquifer systems for this area: (1) the Holocene flood-
plain aquifer; (2) the Pleistocene systems comprised of a perched aquifer, a
shallow artesian aquifer and a deep artesian aquifer; and (3) the Precambrian
- 36 -
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R23W
R22W R21W
R20W
R19W
Isopach Interval: 1000ft.
Map Scale: 1:500/500
Refer to basin no. 4
Isopach of Cenozoicfill in the Kalispell Valley
Figure II-9
- 37 -
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bedrock aquifer. Values for hydraulic conductivity contrast sharply, depending
on the nature of the sediments. Glaciofluvial deposits have high values for
conductivity and are capable of producing yields exceeding 3,000 gpm, as is the
case of a 400-foot well drilled in SE^s NWJj sec. 27, T. 29 N., R. 22 W. Wells
completed in till that has poor hydraulic conductivity, however, usually yield
less than 5 gpm.
The availability of potable ground water in the Kalispell valley is very
good. Wells capable of yielding large amounts of water for irrigation or
municipal supplies can generally be found in the deeper artesian aquifer. Do-
mestic and stockwater wells producing from 10 to 20 gpm are common throughout
the valley at shallow depths.
Values for dissolved solids average approximately 400 mg/L. The general
water quality of glacial deposits is a dominantly calcium-bicarbonate type which
results in hard water. Recharge to the hydrogeologic system is primarily from
rainfall and snowmelt water infiltrating along the mountain fronts, with a minor
amount from irrigation return flow and leakage from overlying aquifers. Most
discharge is from evapotranspiration and wells, with the remainder occurring
through springs and effluent streams.
Currently, the area along Highway 93 between the cities of Kalispell and
Whitefish is rapidly developing, thus placing increased demands on the ground-
water resources. The potential problem of lowering the potentiometric surface
in the area is becoming more and more relevant. A comprehensive study of that
area should be undertaken to determine the effects development is creating and
to evaluate the ground-water resources for future development.
Swan Valley
The Swan valley is located along the eastern branch of the Rocky Mountain
- 38 -
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Trench at its southern end. The Precambrian Belt strata of the Mission Range
on the west and Swan Range on the east dip gently eastward, forming the valley
margins. The valley manifests an asymmetry about its north-south axis, which
is a surface expression of the controlling Swan Fault. Gravity data, however,
demonstrate unequivocally that major faulting occurs at the valley's boundary
with the Mission Mountains, although maximum depth to bedrock is nearer the
Swan Range (Crosby, 1968). The valley fill attains a maximum thickness of
6,500 feet approximately five miles north-northwest of Condon (Figure 11-10).
The valley began filling initially with material derived from the adjacent
mountains during early Tertiary time. Tertiary or early Pleistocene sediments
along the Swan River (T. 25 N.) are described by Alden (1953) as being rusty,
clayey sand and buff sandy clay, with some gravel in which some of the pebbles
are badly decomposed. They are overlain by lighter-colored, grayish glacial
drift containing striated pebbles. Elsewhere, Tertiary sediments are not exposed
because they have been eroded, reworked or buried by glacial deposits. Retreat-
ing glaciers of Wisconsinan age have mantled the floor of the Swan valley with a
substantial thickness of glacial drift. These glaciofluvial and till deposits
may be several hundred feet thick.
The hydrogeology of the Swan valley is rather complex as a result of
glaciation. Pleistocene and Recent alluvial sediments form the principal aquifers
of the valley. A review of well logs within the valley determined that most wells
were completed in till. Well yields are generally small, ranging from 1/2 to 50
gpm; an exception is the Forest Service's 330-gpm well at Condon. The average
well yield is approximately 12 gpm. Ground water from the till is of good
chemical quality and is used mainly for domestic purposes. The glacial till has
low permeability in the center of the valley where most of the wells are drilled,
but because sorting of deposits by proglacial streams occurred along the eastern
- 39J -
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R18W R17W R16W R15W
Isopach Interval: 1000 ft.
Map Scale: 1:500,000
Refer to basin no. 7
Isopach of Cenozoic fill in the Swan Valley
Figure 11-10
- 40 -
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margin, well yields would likely be higher there. The alluvium bordering the
Swan River serves as the other reliable source of ground water. Well depths are
shallow, and sufficient quantities for domestic and stockwater use are easily
obtained, making the alluvium a desirable source. North of Summit Lake, shallow
ground water moves northward toward Swan Lake; south of the lake the flow is in
a southerly direction.
Because of the paucity of information on the Tertiary deposits and scarcity
of deep lithologic well logs, very little is known on the composition, water-
bearing potential and general nature of these sediments.
Recharge to the aquifer system is from precipitation and snowmelt infiltra-
tion along the mountain fronts. Discharge occurs through springs and wells, and
ground water maintains a base flow for the Swan River during periods of low flow.
Mission Valley
The Mission valley lies in the southernmost extension of the Rocky Mountain
trench. The eastern side of the valley is extremely linear, which is indicative
of the Mission fault. This fault is a high-angle, normal fault with an apparent
stratigraphic throw of about 15,000 feet down to the west. The southern border
of the valley also has a linear expression which represents the St. Mary's fault
zone. Because of the Mission fault, the valley has a distinct north-south align-
ment. Cenozoic fill is deepest near the east-central margin of the valley
(approximately 4,000 feet to the Precambrian basement) and progressively thins
to the west. Isopach contours have an elongated pattern, and this trend probably
continues under the southern shoreline of Flathead Lake (Figure 11-11). Gravity
data west of the large Mission valley manifest a smaller valley, structurally
independent of the main basin. This valley is also elongated along a north-south
axis and attains a maximum depth of 3,000 feet. Preliminary geologic mapping by
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T24N
T23N
T22N
T21N
T20N
T19N
< T18N
R24W
R23W
R22W
R21W
R20W R19W
R1BW
Isopach Interval: 1000 ft.
Map Scale: 1:500,000
Refer to basins no. 8 and 9
Isopach of Cenozoic fill in the Mission and Little Bitterroot Valleys
Figure 11-11
- 42 -
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Harrison and others (1974) revealed that an anticlinorium coincides with the
axis of this fault-bounded valley.
The oldest rocks in the valley are of Precambrian age. They are probably
overlain by Tertiary sediments; however, no reference has been found of Tertiary
outcroppings or presence on well logs. Overlying the Tertiary strata are
Quaternary glacial and lake-bed deposits and Holocene alluvium. The Precambrian
rocks, for the most part, are argillites with some quartzites and limestones
present. Wells or springs which tap these sediments along fractures usually
yield less than 10 gpm. The potential for ground water in Tertiary sediments
is unknown because of its uncertain presence.
Glacial deposits are the most important source of ground water in the
Mission valley, but well yields are unpredictable because of the heterogeneity
of the aquifer material. Wells drilled in morainal material generally yield
small amounts of water, but there are large-capacity wells of more than 300 gpm
tapping glacial deposits near Ronan and Poison (Boettcher, 1980). In some areas
a confining layer overlies glacial or alluvial deposits, creating flowing
artesian conditions. Flowing wells yield as much as 600 gpm near Ronan (Boettcher,
1980). Dissolved solids have an average value of around 350 to 400 mg/L, and the
chemical quality of ground water derived from glacial deposits is generally good.
Well yields range from 10 to 400 gpm for the alluvial aquifer. These yields
are largely dependent on location and well completion, with the average yield
approximately 40 to 50 gpm. The alluvial aquifer serves as a potable source for
numerous domestic and stockwater wells. Overall water quality of the alluvium
is good, but the water is somewhat hard. Recharge to the aquifer system is from
precipitation, snowmelt runoff, influent streams and irrigation return flow.
Discharge occurs from well pumping, springs and evapotranspiration. Ground water
is a valuable resource for the inhabitants of the Mission valley. Whereas all
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the towns in the valley depend partly or entirely on ground water for their
supply, the rural residents are totally dependent on wells and springs.
Little Bitterroot Valley
The Little Bitterroot valley is a structural depression, probably bounded
by high-angle, normal or listric normal faults of Tertiary age (Donovan and
Sonderegger, 1981). Geologic mapping by Harrison and others (1974) showed a
series of north-northwest-trending normal faults transecting the valley. En-
compassing the valley are various Precambrian formations. A geothermal test
well near Campaqua encountered what was thought to be Precambrian Ravalli Group
rock at 264 feet below land surface. Gravity data demonstrate a bedrock high
at this well site and also suggest that the Cenozoic fill rapidly deepens
approximately three miles due west. The fill attains a maximum thickness of
more than 2,000 feet in the south-central part of the valley based on gravity
data calculations (Figure 11-11).
Although Tertiary sediments were absent in the geothermal test well, there
are Tertiary outcroppings of volcanoclastic sandstones and conglomerates, ash
layers and fluvial sediments along the northern margins of the valley. It is
likely that similar Tertiary deposits overlie the Precambrian bedrock floor in
the deeper segment of the valley, but may have been removed by Pleistocene
glacial erosion in localized shallow areas. Glaciofluvial and glaciolacustrine
deposits unconformably overlie Tertiary and Precambrian rocks and can be con-
tinuously correlated over the entire basin. Donovan and Sonderegger and others
(1981) described a permeable Pleistocene gravel bed, estimated to be 20 to 60
feet thick, occurring extensively throughout the valley. The top of the gravel
bed appears to be nearly planar and is overlain by 200 to 300 feet of homogenous
silty clays of glacial Lake Missoula. These silts are surficially present over
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most of the valley. The Little Bitterroot River has deposited an alluvial veneer
along the eastern margin of the valley.
The hydrogeology of the Little Bitterroot valley is extremely complex be-
cause of the interrelationship of the separate aquifers. Deep fractures in the
Precambrian rocks provide conduits for the circulation of hydrothermal waters.
Localized hot and warm springs issue from these fractures. Wells reaching this
aquifer have yields of up to 800 gpm and water temperatures of approximately
45°C. Although the water is somewhat mineralized by sulfate, manganese and iron,
it is generally softer because of the higher sodium concentration. Average values
for dissolved solids are approximately 400 mg/L. The potential availability of
ground water in Tertiary sediments is presently unknown, though Boettcher (1980)
believed water from these deposits has high iron concentrations.
Locally, the aforementioned Pleistocene gravel aquifer appears to be
hydraulically interconnected with the Precambrian system and probably recharged
through vertical leakage and infiltration. This aquifer produces flowing artesian
wells and is widely used for irrigation in the valley. Water levels in wells
penetrating this aquifer decline during the irrigation season and rise the rest
of the year. Long-term records (8 years) show a net water-level decline in the
area, probably owing to the large number of flowing irrigation wells (Boettcher,
1980). It appears this gravel aquifer has reached its appropriation limit, and
further exploitation may result in lowering of water pressures to the point that
wells will no longer flow. The overall water quality is generally good. Ground
water from the alluvium of the Little Bitterroot River is moderately used. Wells
tapping the alluvial aquifer are producing substantial yields, but it is used
principally for domestic and stockwater purposes.
Recharge to the ground-water system is from precipitation, snowmelt runoff
and irrigation return flow. Discharge is primarily the result of irrigation
wells, springs and evapotranspiration.
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Missoula-Ninemile Valley
The Missoula and Ninemile valleys form an elongated northwest-trending
trough approximately 42 miles long that is commonly referred to as the Missoula
basin. Geomorphically represented as a linear succession of truncated spurs
along the southern margin of the Reservation Divide Mountains, the Ninemile
fault delineates the northeastern edge of the valley. The southwest side of
the valley is formed by the Bitterroot Range and the Ninemile Divide Mountains.
The basin was formed by extensional faulting that downdropped the bedrock floor
during early Tertiary time. Contemporaneous with downfaulting, the basin began
filling with detritus eroded from the surrounding mountains into which were
interbedded layers of volcanic ash. The resultant deposits of interbedded shale,
ash and conglomerate were subsequently mantled by a few hundred feet of well-
sorted channel gravel and sand of Pliocene age (McMurtrey and others, 1964).
The Clark Fork River has dissected the valley deposits and has mantled the glacial
sediments with an alluvial veneer along its course. The sediments have a cumula-
tive thickness of more than 3,000 feet near the airport (Figure 11-12).
There are three basic aquifer units within the Missoula basin: Holocene
to Pliocene unconsolidated deposits forming the flood plain of the Clark Fork
River and the remainder of the valley floor; Tertiary sediments of the Oligocene
age that underlie the alluvium or border it as terrace deposits; and a Precambrian
bedrock aquifer. The alluvium is composed of discontinuous layers of gravels,
sand and clay that range in thickness from a few feet to 250 feet; the maximum
thickness is near the mouth of Grant Creek (Geldon and Curry, 1978). Well yields
vary depending upon use; some large irrigation and municipal wells have yields
in excess of 4,000 gpm. The chemical quality of water from the alluvium is
generally excellent; the average dissolved-solids concentration is 175 mg/L.
Alluvial ground waters are generally a calcium-bicarbonate type and are, therefore,
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T1 7N
T16N
T15N
T14N
T13N
T12N
R24W
R23W
R22W
R21W
R20W
R19W R18W
Isopach Interval: 1000 ft.
Map Scale: 1:500,000
Refer to basin no. 14
Isopach of Cenozoic fill in the Missoula-Ninemile Valley
Figure 11-12
- 47 -
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moderately hard. Recharge to this system is from precipitation, irrigation
return flow and losing streams. Aquifer discharge is from well pumpage, evapo-
transpiration, seepage to underlying units and losses to maintain stream base flow.
The Oligocene sediments are characterized as semiconsolidated, bedded deposits
of sand, silt, clay, ash and gravel; these rocks underlie Holocene to Pliocene
sediments but are best exposed as sloping sediments. Well yields from these
deposits are generally small, ranging from 1 to 20 gpm, because of the fine-
grained nature of the sediments. Tertiary rocks account for most of the valley
fill and may be up to 3,000 feet thick. Dissolved-solids content of ground water
from Tertiary sediments averages 300 mg/L, which is quite low. Because well
yields are small, the ground water is generally used for domestic and stockwater
purposes. Recharge is from precipitation and infiltration from the overlying
alluvium. Discharge occurs from springs and well pumpage.
The Precambrian bedrock aquifer is of only minor importance because it is
relatively impermeable. Fracture systems within the bedrock yield small quan-
tities (1 to 5 gpm) of water. Little is known of the water quality of this
aquifer, but the water appears to be potable.
Blackfoot Valley
Although gravity data suggest that the Blackfoot and Nevada valleys are
separate basins, they are topographically continuous. For this reason they are
jointly referred to as the Blackfoot valley in this report. This intermontane
valley, located in the northern part of Powell County, has a general northwest
trend. The Blackfoot Mountains, composed of Belt Supergroup rocks, form the
northeastern border of the valley. At the base of this range is an unnamed
valley-margin fault. It is a high-angle, normal fault dipping to the southwest
- 48 -
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(Witkind, 1975). The northwestern part of the Garnet Range forms the south-
western border of the valley. These mountains are also composed of Precambrian
Belt Supergroup rocks. Small bodies of quartz monzonite occur locally in the
strata, and extensive Tertiary basalts and andesites outcrop near Helmville.
Block faulting and tilting occurred intermittently during deposition and
continued in late Oligocene and (or) early Miocene time, after which the region
was deeply eroded (Cantwell, 1980). Again, during late Miocene and Pliocene time,
block faulting recurred, and detritus eroded from the surrounding mountains, in-
filling the basin. During Pleistocene time, glaciers advanced and retreated
across the valley. Deposits of glacial outwash and till cover most of the
Tertiary valley-fill deposits north of Helmville. The low rolling hills that
dominant the present valley floor were formed by the glaciers (Cantwell, 1980).
Quaternary stream and fan alluvium mantles the glacial deposits in some locales.
Gravity data indicate that the Tertiary and Quaternary deposits attain a maximum
thickness of more than 6,000 feet near the center of the valley (Figure 11-13).
It is assumed that similar Belt Supergroup rocks underlie Cenozoic sediments.
Ground water in the Blackfoot valley is derived mainly from the Quaternary
alluvial and glaciofluvial deposits. These deposits are composed of unconsoli-
dated gravels, sands, silts and clays that are moderately well sorted. The
average thickness of the alluvium along the Blackfoot River is probably 80 to
100 feet. Wells completed in alluvial and glaciofluvial sediments generally
produce good-quality water that has concentrations of dissolved solids ranging
between 150 and 250 mg/L. Well yields for the alluvial aquifer are usually
about 20 to 25 gpm. Glacial till covers much of the Blackfoot valley. The till
consists of a heterogeneous mixture of unsorted and unconsolidated gravels and
boulders in a silty to clayey matrix. The till can be up to 150 feet thick but
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Isopsch Interval: 1000 ft.
Map Scale: 1:500,000
Refer to basin no. 18
Isopach of Cenozoic fill in the Blackfoot Valley
Figure 11-13
- 50 -
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has low well yields ranging from 5 to 15 gpm. Underlying the glacial and
alluvial deposits is Tertiary valley fill. The Tertiary sedimentary rocks in
this area are a semiconsolidated, light-gray, sandy clay containing interbedded
lime marl and conglomerate. These sediments have a high percentage of fine-
grained materials and are therefore not very permeable. Well yields are small
from Tertiary sediments, averaging about 5 gpm.
Precambrian metasediments and Tertiary volcanic rocks serve as another
source of ground water. Generally, wells completed in these rocks yield only
small quantities of water from fractures. However, there are two large-capacity
wells in T. 12 N., R. 12 W., sections 23 and 28, that produce 3,000 and 350 gpm,
respectively. It is believed the wells are completed along a fracture network
in Tertiary basalts.
All the geohydrologic units in the Blackfoot valley are recharged directly
or indirectly by precipitation. Rain, snowmelt runoff and influent streams
account for most of the recharge. Ground water is discharged to springs,
effluent streams and to the atmosphere by evapotranspiration. Discharge by wells
is minimal, even though most residents use water supplied by wells.
Prickly Pear Basin (Helena Valley)
The Prickly Pear basin, or Helena valley, is roughly a nearly circular
basin surrounded by mountains—the Big Belt Mountains on the north; Scratch-
gravel Hills on the west; Elkhorn Mountains on the south; and Spokane Hills on
the east. Drainages between each of these mountain ranges lead to other Cenozoic
basins. Most of the bedrock exposed in the mountains east, north and west of the
Helena valley belong to the Belt Supergroup. Paleozoic and Mesozoic rocks out-
crop along the southern valley margin. Granodiorite and related rocks of the
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Late Cretaceous Boulder batholith intruded and metamorphosed sedimentary rocks
along the south and west margins of the Helena valley. At the southern edge of
the valley, the Elkhorn Mountain Volcanics overlie sedimentary and intrusive
rocks in the northern Elkhorn Mountains.
The Helena valley is a northwest-trending structural and topographic basin,
which began to form in early or middle Tertiary time by block faulting, possibly
along preexisting zones of basement weakness. Two major northwest-trending
fault zones bound the valley. The Prickly Pear fault zone (northeast side down)
roughly parallels the southwest valley margin. A 9.5-mile segment, half the
total trace length of the Prickly Pear fault zone, lies buried beneath young
alluvial deposits in the western part of the valley. A part of the Lewis and
Clark line, the Helena valley fault zone (southwest side down) consists of five
segments that form the northeast valley margin. The western segments are remark-
ably linear and appear to offset middle Pleistocene deposits. Along the south-
west side of this fault zone, basin-fill deposits reach a maximum thickness of
6,000 feet and average over 3,000 feet thick along most of the fault's length
(Figure 11-14). The sediments gradually thin in the western and southern parts
of the valley. Numerous small faults near the southern Scratchgravel Hills and
along the northwest valley margin offset deposits as young as late Pleistocene
but do not appear to define an extensive fault zone.
The oldest recognized Tertiary clastic deposits include well-bedded olive-
gray to yellowish clay; tan siltstone; light-gray, poorly sorted, arkosic sand;
rounded to subangular pebble gravel; and thin lignite beds of probable Oligocene
age. Rocks of similar age outcrop along the southern valley margin and include
white to gray, well-indurated, volcaniclastic rocks containing pumice fragments
and rhyolite pebbles. The Tertiary deposits covering 80 percent of the eastern
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R6W R5W R4W R3W R2W R1W
Isopach Interval: 1000 ft.
Map Scale: 1:500,000
Refer to basin no. 21
isopach of Cenozoic fill in the Prickly Pear Basin
Figure 11-14
- 53 -
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Helena valley consist of tan, micaceous siltstone with interbedded, sandy pebble
and cobble gravel. Probably middle Miocene to Pliocene in age, this siltstone
is generally coarser grained than the Oligocene deposits. Early Pleistocene and
possibly latest Tertiary alluvial deposits cap ridge tops along the southern
valley margin and form eroded and faulted hills along the northeast portion of
the Helena valley. A veneer of poorly sorted, silty gravel covers extensive
pediment surfaces developed along the northwest and southwest perimeter of the
valley. Late Pleistocene to Holocene alluvial-plain deposits, which overlie the
western Helena valley, probably do not exceed 150 feet in thickness. Other un-
consolidated deposits outcropping over relatively small areas include channel
and terrace alluvium, loess, strath terrace remnants along the Missouri River,
and fine sand, silt, clay and minor gravel deposits of glacial Lake Great Falls
(Stickney and Bingler, 1981).
Ground water in the Helena valley is derived from three separate aquifer
units; distinction of these units is based on their relative geologic ages and
lithologic characteristics. The units are 1) a bedrock aquifer; 2) Tertiary age
sediments; and 3) various deposits of Pleistocene and Holocene times.
The bedrock aquifer consists of a variety of sedimentary rocks ranging
from Precambrian to Cretaceous age, and Late Cretaceous and early Tertiary
igneous rocks. The oldest rocks of the valley are the Precambrian metasediments
belonging to the Belt Supergroup. They are composed of red, green and brown
argillites and red and white quartzites, which outcrop along the east, west and
north margins of the valley. Paleozoic and Mesozoic rocks made up of brown to
white quartzite and sandstone, black to brown shale, and bluish-gray to tan
limestone and dolomite are exposed along the southern valley border (Stickney,
1981). In some locales, the eastern extension of the Boulder batholith has in-
truded and metamorphosed the preexisting sedimentary rocks of the southwestern
- 54 -
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margin. Andesites and tuffs of the Elkhorn Mountain Volcanics have also inter-
divided and overlie sedimentary rocks in the southern portion of the valley.
For the most part, these rocks are well indurated and contain no interstitial
water. Wells drilled along the periphery of the Helena valley are completed in
this bedrock aquifer and attempt to intersect bedrock fractures of joints to
obtain sufficient yields. Well yields usually average 5 to 10 gpm and are of
good chemical water quality for domestic and stock use.
Sediments of Tertiary age comprise another aquifer unit in the valley but
also have limited use. These sediments, which overlie bedrock and underlie.
Quaternary deposits, account for the major portion of basin-fill deposits.
Tertiary sediments outcrop in the southern part of the valley and cover a large
area in the eastern part of the valley. In general, the basin-fill deposits are
composed of detrital materials eroded from the surrounding mountains. The oldest
recognized Tertiary deposits include well-bedded, olive-gray to yellowish clay;
tan siltstone; light-gray, poorly sorted arkosic sand; rounded to subangular
pebble gravel; and thin lignite beds probably of Oligocene age (Stickney, 1981).
Interbedded volcanic ash and flows of similar age are exposed along the southern
border of the valley. Overlying the Oligocene deposits are Miocene and Pliocene
age sediments. These coarser-grained sediments are composed of gravels and sands
in a silty clay matrix and are laterally discontinuous. Exposed Tertiary sediments
are generally unconsolidated and tend to become semiconsolidated with depth of
burial.
The fine-grained nature of these sediments limits the permeability of this
aquifer unit. Most wells obtaining ground water from Tertiary sediments have
yields of 15 to 30 gpm, but some of the deeper wells have yields in excess of
200 gpm. In some cases, wells have tapped confined water-bearing zones that
- 55 -
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yielded water under artesian conditions. These wells are in the lower part of
the valley and include wells at the Masonic Home in T. 11N., R. 3 E., section 2,
and at the Montana State Vocational School in T. 11 N., R. 3 W., section 34
(Lorenz and Swenson, 1951). The overall ground-water availability from this
aquifer unit is highly variable and dependent upon location and the composition
of the deposits. This ground water is somewhat hard, but it is suitable for
domestic, stockwatering and irrigation purposes. Some wells produce water with
iron and manganese concentrations higher than recommended limits for potable
supplies. Although these concentrations are not detrimental to health, they
give the water an undesirable taste and stain fixtures reddish-brown. A possible
source of these chemicals is the solution of iron and manganese oxides that have
formed coatings on the gravel and boulders in the basin-fill deposits (Wilke and
Coffin, 1973).
Pleistocene and Holocene deposits serve as the most prolific and readily
available source for ground water in the Helena valley. Late Pleistocene to
Holocene unconsolidated alluvial-plain deposits mantle the floor of the Helena
valley. These deposits are composed of a heterogeneous mixture of gravels, sands,
silts and clays and are usually moderately sorted from fluvial processes. A
large portion of the finer-grained material is carried off downstream. This loss
of fine-grained material enhances the permeability of these sediments. The sand
and gravel layers of this aquifer yield water freely to wells but often inter-
finger with impermeable clay beds and, for this reason, are laterally discontinuous.
Because of the heterogeneous nature of the sediments, the layers of sand and
gravel form a complex, but generally interconnected, system of aquifer zones that
are considered as one multiple-aquifer system. Several large-capacity wells
(pumping in excess of 500 gpm) have been constructed, and most irrigation wells
- 56 -
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derive their supply from these sediments. A transmissivity of about 10,000
gallons per day represents a reasonable estimate for the alluvial aquifer pene-
trated by most shallow wells in the southern part of the valley (Moreland and
Leonard, 1980).
A thin veneer of poorly sorted gravel covers extensive pediment surfaces
of middle Pleistocene age. These surfaces are extensively developed along the
northwest and southwest sides of the Helena valley. Most of the city of Helena
is built on such deposits. These deposits have a moderate degree of permeability
and supply ample water for domestic and stockwater uses. Other unconsolidated
deposits that outcrop over relatively small areas throughout the basin include
loess deposits, strath terrace remnants along the Missouri River and lacustrine
silts and clays of glacial Lake Great Falls. They are only of nominal importance
because their well yields are very small.
With few exceptions, ground water from this aquifer is of good to excellent
quality. Chemical analyses show the water is dominantly a calcium bicarbonate
type; however, a well's proximity can influence the type. Although there is
variation in some instances, the concentration of dissolved solids in water from
most wells sampled in the valley is less than 400 mg/L.
Infiltration from rainfall, snowmelt runoff and irrigation return flows
accounts for most of the recharge to the aquifer system. Other sources of re-
charge are influent stream losses and inter-aquifer leakage. Ground-water
discharge in the valley occurs from evapotranspiration, wells, springs, seeps
and losses to effluent streams.
Bitterroot Valley
The Bitterroot valley is topographically expressed as a wedge-shaped inter-
montane basin in west-central Montana. The valley's asymmetry about its north-
- 57 -
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south axis is a surface expression of the controlling Bitterroot fault along the
western margin of the valley. This high-angle, normal fault dips steeply to the
east and forms the triangular facets on the eastern face of the Bitterroot Range.
Activity along the fault may have been as recent as historic time (Witkind, 1975).
The Bitterroot Range is a high-grade metamorphic complex derived from lower
Beltian sedimentary rocks that border the Idaho batholith (Wehrenberg, 1968).
The Sapphire Mountains form the eastern border of the valley. The northern por-
tion of the Sapphire Mountains is composed of Precambrian Belt sediments, whereas
the southern portion is Cretaceous to early Tertiary granitic rocks.
The surface of the Bitterroot valley is largely an alluvial flood plain but
also has low to moderately high gravel-veneered Tertiary terraces along the
eastern margin. Except for an area of Tertiary volcanic rocks south of Hamilton,
the west side of the valley appears to be underlain by later (Quaternary) alluvium,
including glacial moraines and outwash from the Bitterroot Range (Pardee, 1950).
The alluvium, glacial deposits and Tertiary tuffs and sediments together compose
the valley fill. Gravity data suggest that these Cenozoic sediments attain a
thickness of more than 3,000 feet between the towns of Woodside and Corvallis
(Figure 11-15). The isocontours also show that the valley fill thins in the
vicinity of the town of Victor. This apparent bedrock high is probably related
to a thinner section of valley fill rather than to a bedrock-density change. It
should be noted that the contour pattern along the east margin of the valley is
very irregular, indicating that the eastern wall of the Bitterroot valley has a
different structural origin than the western margin (Lankston, 1975).
Although the Bitterroot valley has been besieged by residential development,
there still exists only sparse data concerning ground water deeper than 100 feet.
This is because the alluvial sediments of the Bitterroot River are widespread
and capable of sufficient yields of good-quality water for domestic and stock use.
The alluvium is composed of unconsolidated gravels, sands, silts and clays.
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TUN
T10N
R22W R21W R20W R19W
soDach Interval: 1000 ft.
M-ap Scale: 1:500,000
Refer to basin no. 25
isopach of Cenozoic fill in the Bitterroot Valley
Figure 11-15
R18W
- 59 -
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These sediments dominantly have a high percentage of coarse-grained materials
because the finer fraction is carried downstream. This results in a higher
degree of permeability. The alluvial aquifer of the Bitterroot River is thick-
est in the center of the valley and progressively thins towards the valley
margins. Wells in the alluvium generally yield between 15 and 25 gpm, but the
potential for larger capacities is readily available. Concentrations of dis-
solved solids in the alluvium range from 40 to 705 mg/L for springs and wells.
Glaciolacustrine and morainal deposits along the western and southern
borders of the valley are grouped as another aquifer. These deposits have a
large percentage of fine-grained materials and, therefore, have low permeabil-
ities. The thickness of the glacial sediments varies considerably depending
upon location; however, well yields are consistently small—usually averaging
5 gpm.
Underlying and bordering the Quaternary deposits are unconsolidated to
semiconsolidated Tertiary sediments. These sediments consist of arkosic channel
sand containing thin lenses of gravel eroded from the surrounding mountains,
occasional lacustrine silts and clays and some beds of volcanic ash. Within
short distances, materials of different textures interfinger and intergrade,
both laterally and vertically, in accordance with changes in the original environ-
ments of deposition and with the degree of volcanic activity in the region
(McMurtrey and others, 1959). Tertiary deposits contain a large percentage of
fine-grained materials that greatly inhibit the permeability of the sediments.
A preliminary evaluation of numerous deep aquifer zones was recently completed.
Tmnsmissivities ranged from low values of 25 and 122 gallons per day per foot
(gpd/ft) to higher values of 1,650 and 3,750 gpd/ft. Calculated values for
storage coefficients varied from 0.00005 to 0.35 (Norbeck, 1980). Wells completed
in Tertiary sediments usually have yields of 8 to 12 gpm, but there are some
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large-capacity municipal wells in the valley. The city of Stevensville has a
well drilled to 460 feet that produces 400 gpm. Tertiary ground waters are
generally of good chemical quality but commonly have moderate concentrations
of iron. A geothermal study has also been completed on numerous deep Tertiary
test wells in the valley. The study determined there is no evidence for hydro-
thermal discharge (Leonard and Wood, 1980).
Annual precipitation for this area is approximately 16 inches per year,
which contributes to recharging the ground-water system. Other forms of recharge
are irrigation return flows, influent streams and inter-aquifer leakage. Ground
water in the valley is discharged by evapotranspiration, effluent streams,
springs, seeps and wells.
Deer Lodge Valley
The Deer Lodge valley is located west of the Continental Divide (locally
known as the Deer Lodge Mountains) and east of the Flint Creek Range. To the
north is the Garnet Range, and to the south, the Anaconda Range. In general, Pre-
cambrian through Mesozoic sediments outcrop on the west and north sides of the
valley, and Tertiary volcanics and Cretaceous intrusions outcrop to the south,
east and north. The Anaconda and Flint Creek ranges contain Precambrian through
Cretaceous sedimentary rocks with numerous Cretaceous intrusions. To the east,
the Boulder batholith quartz monzonite and Lowland Creek Volcanics make up the
mountains of the Continental Divide (Sonderegger and others, 1980). Extensive
andesite flows are found on the east side and at both ends of the valley
(Cremer, 1966).
The Deer Lodge valley probably began forming as a shallow topographic low
in response to batholithic intrusion and doming of country rocks. Later, block
faulting increased the topographic relief. Fault scarps of the Powell fault
zone are evident along the western margin of the valley (Cremer, 1966). At the
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base of the Continental Divide mountains, gravity data indicate another major
fault along the eastern edge of the valley (Sonderegger and others, 1980).
The basin began filling with sediments during the Oligocene Epoch. Some
uncertainty exists concerning the actual thickness of basin-fill deposits in
the Deer Lodge valley. Gravity profiling of the valley indicates a maximum
thickness of 6,000 feet near the center of T. 5 N., R. 10 W. , but in the center
of the valley, south of Deer Lodge, an exploratory oil well recently penetrated
10,300 feet of Cenozoic sediments (Montana Oil Journal, 12/31/81). Original
gravity profiles for the same region indicate a maximum depth of 3,000 feet to
bedrock. Figure 11-16 shows the Deer Lodge basin-fill thickness contoured from
available gravity data. The location of the exploratory well and the basin-fill
thickness are included to give an idea of the uncertainty of the gravity infor-
mation. One reason that gravity data do not coincide with drill-hole data is
the large amount of Tertiary volcanics interbedded with basin-fill deposits
throughout the valley. These volcanics increase the density of the Deer Lodge
basin fill as a whole and influence gravity measurements in the field. Unless
the increased density is taken into account during computer modeling of the
gravity data, the resulting basin depths are also distorted. As a part of the
same problem, gravity profiles show a bedrock high in the center of the valley.
This high is a reflection of lava flows concentrated in the center of the valley
(Konizeski and others, 1968). Before contouring the basin-fill isopach, the
gravity profiles were 'smoothed' to eliminate the false high.
The basin is filled with unconsolidated to consolidated sediments and inter-
bedded volcanics, ranging in age from Oligocene to Holocene. Oligocene bentonitic
conglomerate and arkose of Oligocene age are overlain by Miocene unconsolidated
to well-consolidated fluvial clays, silts, sands and pebble conglomerates.
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R12W R11W
R10W R9W
R8W
Isopach Interval: 1000 ft.
Map Scale: 1:500,000
Refer to basin no. 28
Isopach of Cenozoicfill in the Gteer Lodge Valley
Figure 11-16
- 63 -
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Pliocene deposits include cemented colluvium and fan deposits near the valley
margins. The deposits grade into flood plain and channel deposits toward the
center of the valley. These Pliocene alluvial deposits consist of interbedded
limestone, shale, sandstone and gravel, with minor pebble and cobble conglom-
erates and varying amounts of bentonitic clay. Three-fifths of the Deer Lodge
valley is mantled by Quaternary flood plain and fan deposits. Other Quaternary
deposits include glacial moraines, travertine (near Warm Springs) and boulder
fields near Warm Springs canyon (Konizeski and others, 1968).
Ground water in the Deer Lodge valley is derived mainly from the alluvium
of the Clark Fork River. Wells completed in this aquifer are generally shallow,
ranging from 10 to 150 feet deep. Water in these Quaternary sediments is gen-
erally unconfined, and the water table fluctuates seasonally. Overall water
quality is good, and the water is suitable for household and stock uses. Well
yields can vary from 5 to 150 gpm, with the average being about 25 gpm.
Tertiary sediments are the other primary source of ground water in the
valley. These rocks either underlie the Quaternary alluvial deposits or flank
the alluvium as deeply incised pediments. Tertiary rocks are composed of finer-
grained sediments that become more consolidated with depth. The water in wells
completed in the Tertiary sediments is generally confined, resulting in artesian
conditions. Because of the low permeability of the Tertiary sediments, well
yields on the average are generally small (15 to 20 gpm); however, there are
exceptions. A well drilled to 436 feet in T. 6 N., R. 9 W. , section 7, is
recorded to produce 2,400 gpm. The city of Deer Lodge is also reported to have
completed a 900-gpm test well. These large-capacity wells are used for irriga-
tion and municipal water systems, respectively.
The ground-water system is recharged partially from precipitation, irriga-
tion return flow and from influent streams. Discharge occurs from springs, wells,
evapotranspiration and effluent streams.
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Townsend Valley
Located along the southern end of the Lewis and Clark line, the Townsend
valley trends roughly northwest between the Elkhorn Mountains on the west and
the Big Belt Mountains on the east. Precambrian through Mesozoic sedimentary
rocks are found on all sides of the valley. On the west and south sides,
Cretaceous and Tertiary volcanics and intrusive rocks outcrop.
The Townsend valley is a graben formed by crustal extension. Faults are
evident along the mountain fronts to the east and west (Reynolds, 1979). In
the north, the graben splits into two parts around the Spokane Hills horst
(Kinoshita and others, 1964). To the east of the horst, the graben comes to an
abrupt end against faults of the Lewis and Clark line. On the west side of the
Spokane Hills, the Townsend valley extends into the Helena valley. These basins
developed together in early Tertiary time; later, the drainage between them
became blocked by a broad bedrock ridge (Davis and others, 1963). Tertiary
deposits located between the two valleys are less than 1,000 feet thick but
thicken abruptly toward the center of either basin. The Townsend valley fill
is more than 8,000 feet thick in the northeast and gradually thins to the west
and south (Figure 11-17). A major fault (east side down) extends southeast down
the center of the valley from the Spokane Hills. At the valley's southern margin,
basin-fill deposits form an irregular contact with bedrock. This contact may be
a depositional feature or may have been formed from a complex of small fault
blocks (Kinoshita and others, 1964).
The graben floor originally dropped with little or no tilting (Davis and
others, 1963). Block faulting, with the major amount of movement along the
Lewis and Clark line and with tilting of the graben floor to the east, continued
intermittently from late Oligocene through Miocene. Throughout the valley,
Tertiary strata have been displaced by small northwest-trending faults and show
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TUN
T10N
T3N
FtlW R1E R2E R3E R4E
Isopach Interval: 1000 ft.
Map Scale: 1:500,000
Refer to ba»in no. 30
Isopach of Cenozoic fill in the Townsend Valley
Figure 11-17
- 66 -
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varying degrees of dip to the east.
The Tertiary deposits in the Townsend valley include the early Oligocene
Climbing Arrow Formation, the middle Oligocene Dunbar Creek Formation and the
Miocene Sixmile Creek Formation (Kinoshita and others, 1964). The Climbing
Arrow Formation consists of light-colored, fine-grained tuffaceous sediments
with small amounts of interbedded sand and gravel. Locally, it contains thin
beds of coal or diatomaceous earth. Above the Climbing Arrow beds, the Dunbar
Creek Formation contains coarse sediments mixed with a large amount of tuffaceous
material. Unconformably overlying the Dunbar Creek Formation, the Sixmile Creek
Formation is a light to buff-colored sandy clay with some sand and gravel beds,
locally overlain by conglomerate. The thin layer of Quaternary alluvium in the
valley consists of fan and flood-plain deposits and a gravel mantle on the
benchlands (Lorenz and McMurtrey, 1956).
The Townsend valley has the most copious ground-water resources of western
Montana's intermontane basins. Numerous large-capacity wells and significant
spring flows issue from the valley sediments. Whereas most intermontane basins
are underlain with Precambrian metasediments or crystaline igneous rocks, this
valley is partially underlain with a stratigraphic sequence of Paleozoic sedi-
ments. It is believed that a direct relationship exists between ground-water
availability and the Paleozoic strata.
Ground water in the Townsend valley is derived from three distinct aquifers:
(1) unconsolidated Pleistocene and Holocene deposits; (2) unconsolidated to semi-
consolidated Tertiary sediments; and (3) bedrock.
The Pleistocene and Holocene deposits are primarily composed of alluvium
of the Missouri River and its tributaries and alluvial fans along the valley
margins. Alluvial deposits are composed of a heterogeneous mixture of cobbles,
gravel, sand, silt and clay. They have been moderately sorted by streamflow,
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which carried the finer-grained materials downstream. Although sand and gravel
beds interfinger with clays and silts, making them discontinuous, the aquifer
is hydraulically interconnected. Alluvial deposits of variable thickness exten-
sively cover the bottomlands from Townsend to Toston and veneer pediment slopes
in the Radersburg area. Most wells completed in the alluvial aquifer are of a
small diameter for domestic and stockwater purposes. These wells generally
range from 25 to 50 feet deep and have sustained yields of 15 to 30 gpm. The
city of Townsend has three wells completed in the alluvial aquifer that are 50,
60 and 93 feet deep; they produce 600, 650 and 440 gpm, respectively. Ground
water from the alluvium is usually of good to excellent quality. Generally the
water from the alluvium is a calcium bicarbonate type. Though the water is
somewhat hard, it is highly suitable for irrigation and domestic uses.
Unconsolidated to semiconsolidated Tertiary sediments underlie the alluvium
and mantle the remainder of the valley floor. The deposits are geomorphologically
expressed as a series of terraces that slope toward the center of the valley. At
the north end of the valley near Canyon Ferry dam, these sediments are comprised
of gravels and cobbles in a sandy-clay matrix representative of broad channel
deposits. In other locales, Tertiary sediments are considerably finer grained
and contain interbedded tuffaceous layers. These fine-grained beds are relatively
impermeable and act as confining layers that produce artesian conditions. Artesian
pressures occur in Tertiary beds that underlie the southern end of the valley and
the area along the west flank of the Dry Creek anticline east of Townsend (Lorenze
and McMurtrey, 1956).
Many large-capacity irrigation wells have been completed in this Tertiary
aquifer. Well depths generally range between 200 and 400 feet. The areas east
and southeast of Canyon Ferry reservoir nave numerous wells with yields in excess
of 1,000 gpm. Wells penetrating Tertiary sediments west of the reservoir, however,
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have yields of 20 to 50 gpm. The ground water is of good chemical quality and
is suitable for domestic, irrigation and stockwater purposes.
Numerous springs with substantial flows also issue from alluvial and
Tertiary sediments. The waters are dominantly a calcium sulfate type, repre-
sentative of the Madison Group. It is supposed that fractures in the Tertiary
sediments act as conduits for water discharging from the Mission Canyon Lime-
stone, a member of the Madison Group. Spring flows range from seeps to roughly
20,000 gpm.
The bedrock aquifer consists of Paleozoic and Precambrian sediments and
Cretaceous igneous rocks outcropping along the periphery of the valley. These
contain little interstitial water, and ground water is derived from secondary
permeabilities such as fractures, solution voids and joints. Well yields are
generally less than 10 gpm.
Recharge to the ground-water system of the Townsend valley occurs through
a variety of means. The major sources of recharge are canal losses and irrigation
return flow. A large portion of the valley is inundated, by Canyon Ferry reservoir,
and seepage from the reservoir and influent streams likely contributes to the
system. Inter-aquifer leakage, precipitation and spring seepage account for the
remainder of the recharge.
Large-capacity irrigation wells and evapotranspiration are the primary means
of discharge. Minor amounts occur through effluent streams, seeps and domestic
and stockwater wells.
Three Forks Basin
The Three Forks basin is the largest of the Tertiary basins in Montana.
Most intermontane basins in Montana trend north-south, but the Three Forks basin
is elongated east-west because of the Willow Creek fault, which runs west-northwest
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along the northern part of the valley. Concealed by basin-fill deposits, the
fault's presence has been inferred from gravity data and from the marked change
in bedrock lithology and regional structure across the fault zone (Davis and
others, 1965a). Precambrian through Mesozoic sedimentary rocks crop out in the
low hills to the north of the Willow Creek fault, whereas Precambrian metamorphics
are the most common rocks in the mountain ranges to the east, west and south of
the basin. Elkhorn Mountain volcanics and Tertiary intrusives also crop out to
the west of the basin, and the Cretaceous-Tertiary Livingston Formation is found
to the northeast.
Erosion and tectonism probably played interrelated parts in the origin of
the basin (Robinson, 1963). On the western side, sinuous basin-fill bedrock
contacts indicate a depositional origin, but on the eastern side, movement along
the Bridger Creek fault played a major role in the basin's formation (Mifflin,
1963). The Bridger Creek fault (basin side down) zigzags along the west front
of the Bridger Range and is unlike most mountain front faults which usually are
fairly straight. The valley fill is more than 6,000 feet thick east of Bozeman
along this fault zone (Figure 11-18). On the southeast side of the Three Forks
basin, a high-angle, normal fault (northwest side down) forms the Gallatin
Range front. Another fault (southeast side down) runs roughly parallel to and
2 miles northwest of the Gallatin Range fault, forming a narrow trough about
3,000 feet deep (Davis and others, 1965b). Mifflin (1963) mapped a series of
block faults along the Madison Range front to the southwest of the basin.
Farther to the west, gravity and magnetic data suggest a fault trending west-
northwest along the edge of the valley north of Harrison (Davis and others, 1965a).
Gravity data also show the Jefferson Canyon thrust and Lombard thrust connected
beneath the basin fill. These thrust faults are exposed in bedrock on the west
and north sides of the Three Forks basin.
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R1E R2E R3E R4E R5E R6E R7E
Isopach Interval: 1000ft.
Map Scale: 1:500,000
Refer to basin no. 33
Isopach of Cenozoic fill in the Three Forks Basin
Figure II-18
- 71 -
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In general, the bedrock beneath the basin is an eastward-tilted slab with
a series of troughs and broad, low ridges roughly trending east-west (Davis and
others, 1965b). Lower Tertiary rocks dominate the western portion of the basin
and have been deformed into broad, gentle folds, while upper Tertiary beds
dominant the eastern half of the valley (Robinson, 1961). In the north, the
Tertiary beds have a southeasterly dip (Wantland, 1953).
The basin fill in the Gallatin valley ranges from late Eocene to Holocene
in age (Robinson, 1961). The lower portion of the Tertiary beds consists of a
limestone conglomerate overlain by light-colored, fine-grained, tuffaceous
strata including limestone, siltstone, mudstone and bentonitic clay with inter-
bedded channel sandstones and conglomerates. Robinson (1963) divided these beds
into four formations: Sphinx Conglomerate; Milligan Creek; Climbing Arrow; and
Dunbar Creek. Separated from the Dunbar Creek Formation by a Miocene unconfor-
mity, the upper Bozeman Group beds are a similar sequence of light-colored, fine-
grained tuffaceous deposits with some interbedded conglomerates and sandstones.
Above the Tertiary deposits, a thin layer of Quaternary terrace and flood plain
gravels, cemented fanglomerates and wind-blown silt has been laid down (Hackett,
1960).
The Quaternary alluvial veneer covering the floor of the Three Forks valley
serves as the principal aquifer within the area. This aquifer is composed of
unconsolidated deposits of gravel, sand, silt and clay. Although it is a pro-
lific aquifer, agricultural and subdivision development is rapidly approaching
the appropriation limit. The aquifer is characterized by generally high values
of transmissivity—100,000 to 300,000 gallons per day per foot—and, in many
places, yields ample water for irrigation (Hackett and others, 1960). Well
depths vary from 10 to 120 feet, and well yields range from 10 to 2,000 gpm from
the aquifer. Chemically, water in the alluvium is a calcium-magnesium-bicarbonate
type, and is suitable for domestic, stock and irrigation uses. Values of dissolved
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solids average around 250 to 300 mg/L.
Underlying the alluvial veneer are semiconsolidated Tertiary sediments.
Characteristically, these sediments have a low permeability as a result of their
lithologic nature. The Tertiary strata have low values of transmissivity (gen-
erally less than 6,000 gpd/ft) and yield sufficient water for only stock and
domestic use (Hackett and others, 1960). Domestic- and stock-well yields
usually average about 15 gpm. However, recent deep wells completed in the Ter-
tiary are now producing yields in excess of 1,500 gpm. The water quality of
Tertiary sediments varies from one locale to the next as well as being a function
of depth. Sodium appears to be a common constituent of ground water from Tertiary
deposits, and there are generally higher concentrations of other minerals.
Recharge to the ground-water system of the Three Forks valley is dominantly
from irrigation return flow and seepage from losing streams. Rainfall and snow-
melt runoff account for only a small portion of the recharge. Ground-water
discharge occurs mainly as evapotranspiration, springs and well pumpage. During
seasonal periods of low streamflow, the alluvial aquifer maintains a base flow
of the rivers.
Cold Spring Valley (North Boulder)
The North Boulder valley is located southwest of the Elkhorn Mountains and
east of Bull Mountain. At the southwest end of the valley, the North Boulder
River joins the Jefferson River. At the southeastern end, Tertiary deposits in
Nigger Hollow extend into the Three Forks basin. Pre-basin rocks surrounding
the valley include the Precambrian LaHood Formation, Paleozoic and Mesozoic
sedimentary rocks and early Tertiary intrusives. Burfeind (1967) found the
valley fill to be a maximum of 4,500 feet thick. At the northwest end of Nigger
Hollow, the Tertiary sediments may be as thick as 1,000 feet (Parker, 1961), but
at the east end, they thin to about 300 feet (Wilson, 1962).
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The Red Lane fault bounds the North Boulder valley on its western side
(Figure 11-19). The fault extends from the Jefferson River along the east side
of Red Hill and through T. 4 N. Alexander (1955) mapped this fault as a reverse
fault with the basin side (east) upthrown. Gravity data of Burfeind (1967)
suggest the fault may be normal with basin side downthrown. Another possible
fault (east side down) runs along the North Boulder River across the northwest
border of Nigger Hollow.
Oligocene and late Miocene strata of the Bozeman Group fill the basin. In
this area the Bozeman Group consists of soft, light-colored, silty, sandy and
conglomeratic vitric tuffs (Alexander, 1955). Large amounts of volcanic glass
are present in various stages of devitrification. Sorting is generally poor,
although a few beds are made up entirely of silt or sand. An unconformity of
early Miocene age-separates the Oligocene and late Miocene strata.
The Cold Springs valley is so named because of the cold springs (approxi-
mately 12°C) that issue from the alluvium, probably discharging from the Madison
near the center of the valley. Presently the springs are nonconsumptively
utilized to support an aquaculture project.
Ground water in the Cold Spring valley is derived principally from the
alluvial aquifer which borders the North Boulder River. This aquifer is lat-
erally quite extensive because of the coalescing flood-plain deposits created by
the river's meandering. The aquifer is composed of gravel, sand and some silt
and may be as much as 80 to 100 feet thick. The variability of the sedimentary
deposits directly relates to variations of aquifer transmissivities. Shallow
wells tapping the alluvium are capable of yields ranging from 10 to 50 gpm and
are used for domestic and agricultural purposes. There are very few irrigation
wells within the valley, but the aquifer appears to be capable of large yields.
A well drilled to 95 feet below the land surface in T. 4 N., R. 3 W., section 1,
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R5W
R4W
R3W
R2W
Isopach Interval: 1000ft.
Map Scale: 1:500,000
Refer to basin no. 34
Isopach of Cenozoic fill in the Cold Spring Valley
Figure 11-19
- 75 -
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is recorded to have a sustained yield in excess of 1,000 gpm. Ground water of
the alluvium is generally hard, potable and of good chemical quality. Based on
water levels in wells along the valley and on the hydrogeological setting, it '
appears that the direction of ground-water flow is from north to south.
Underlying and flanking the alluvial aquifer are sediments of Tertiary age.
These deposits are generally composed of poorly sorted, fine-grained sediments
and characteristically have little storage capacity. Ground-water yields from
these Tertiary sediments are small and only used for domestic and stockwater
purposes. Recharge to the aquifers of the Cold Springs valley is from precipi-
tation and snowmelt, whereas discharge occurs from wells and springs and as
influent streams.
Little Whitetail Creek and Jefferson River valleys
The Little Whitetail Creek and Jefferson River valleys cover about 250
square miles in Madison, Jefferson and Silver Bow counties. These Tertiary
basins are bounded by the Tobacco Root Mountains and Bull Mountains to the east,
the Highland Mountains or Boulder batholith on the west and Bull Mountains to
the north. At its southern limit, the Jefferson valley borders the Beaverhead
valley.
Faults form the eastern boundaries of the basins (Figure 11-20). The
Tobacco Root fault (basin side down) extends along the west front of the Tobacco
Root Mountains. Gravity data (Wilson, 1962) suggest faulting in the subsurface
one mile west of, and roughly parallel to, the mountain-front fault. Kuenzi (1966)
extended the Tobacco Root fault across Tertiary deposits near Whitehall to inter-
sect the Bull Mountain fault on the east edge of Little Whitetail valley. East
of the Tobacco Root fault, the Mayflower Gulch fault (west side down) forms the
east the southeast boundary of a small basin in the Parrot Bench region. Gravity
data from Parker (1961) suggest another fault along the east edge of the shallow
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depression at the eastern end of the Jefferson River valley near Cardwell.
Cenozoic movement along this series of faults (each upthrown on the east),
plus erosion and doming of the Boulder batholith to the west, produced the
Jefferson-Little Whitetail valley, Parrot Bench depression and the small valley
at Cardwell. In early Tertiary time, an irregular erosion surface formed across
the Belt rocks, Paleozoic and Mesozoic sediments, Elkhorn Mountain Volcanics
and Boulder batholith granites of these valleys. Starting in early Oligocene,
Tertiary sediments filled the basins to varying depths (Figure 11-20). The
maximum thickness of Tertiary sediments in the Jefferson-Little Whitetail basin
is 7,000 feet (Burfeind, 1967; Petkewich, 1972). Burfeind (1967) gave a maximum
depth of 3,700 feet for the Parrot Bench depression, but the reconstructed thick-
ness of Tertiary deposits there by Kuenzi and Fields (1971) indicated a maximum
depth of 4,500 feet. Unknown structural complications in the subsurface may
account for the differences. To the east, the small valley at Cardwell is only
about 850 feet deep.
The basins are filled with about 6,000 feet of Tertiary deposits that make
up the Bozeman Group. The lower formation of the group, the Renova, consists of
light-colored, fine-grained strata unconformably overlying pre-basin rocks.
Ranging from 0 to more than 3,500 feet thick, the formation contains alternating
limestones, mudstones, siltstones, sandstones and gravels with a few conglomerates.
More than 70 percent of these sediments are composed of very fine sand or finer-
grained size fraction. Deposition of the Renova Formation ended in middle
Oligocene (or later). A period of erosion followed this deposition and removed
a large volume of Renova strata. Currently, the youngest sediments to be iden-
tified as Renova are middle Oligocene in age.
Deposition of the upper part of the Bozeman Group, the Sixmile Creek Forma-
tion, began in the late Miocene and ended in middle to late Pliocene. Generally
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TTrv :
T5N
T4N
T3N
T2N
TIN
T1S
T2S
T3S
R7W
R6W
R5W
R4W
Isopach Interval: 1000 ft.
Map Scale: 1:500,000
Refer to basins no. 35 and 36
Isopach of Cenozoic fill in the Little Whitetail and Jefferson Valleys
Figure II-20
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darker than the Renova Formation, the Sixmile Creek Formation ranges from 0 to
more than 2,400 feet and consists of coarse-grained sediments. Kuenzi (1966)
described the lithology of the 900-foot type section of the formation as sandy,
gritty, medium to coarse sand (30%), very fine to medium sandstone (21%), sandy
siltstone (11%), mudstone (3%) and marl (7%). Since the late Pliocene, an
unknown amount of Sixmile Creek strata has been removed and locally veneered by
Quaternary deposits.
Most of the wells drilled in these valleys are completed in the alluvium
of the Jefferson River or Little Whitetail Creek. These alluvial aquifers serve
as a reliable ground-water source that can continually produce yields of 50 to
100 gpm. Higher yields necessary for irrigation do not appear to be possible
around the town of Whitehall; however, there does exist a 1,000-gpm irrigation
well in the southern part of Jefferson valley. The water quality of the alluvium
is generally good, with the exception of high iron concentrations in some areas.
It also tends to be slightly hard from the calcium carbonate concentration.
Recharge to the system during the summer and fall months results from influent
streams, whereas during the rest of the year recharge is from precipitation.
Beneath and adjacent to the alluvium are Tertiary sediments that form gently
sloping terraces. As previously mentioned, more than 70 percent of these sedi-
ments are composed of very fine sand or finer-grain size fractions, which results
in a lack of void spaces. A review of well-appropriation data showed only a few
wells completed in Tertiary sediments, and their average yield was 10 to 15 gpm.
Although there is not any water-quality data on these Tertiary wells, the water
is generally considered suitable for domestic and stockwater use. The terraces
are recharged primarily from precipitation, and discharge occurs through wells,
springs, seeps and evapotranspiration.
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Melrose and Beaverhead valleys
The Beaverhead valley is an irregularly shaped basin with one arm extending
southeast between the Tobacco Root Mountains and Ruby Range, and another arm, the
Melrose valley, extending northwest between the Highlands and McCartney Mountain.
A third extension runs along the south side of McCartney Mountain. To the south,
the Beaverhead valley is bounded by the Blacktail Range, and to the west, by the
Pioneer Mountains. The Jefferson valley on the north and the Blacktail valley on
the southeast adjoin the Beaverhead valley.
Tertiary basins in this region formed by block faulting, with some basins
bounded on both sides by faults (Chandler, 1973). In the Beaverhead valley, the
east side has been tectonically active, whereas little evidence of activity is
seen to the west (Hoffman, 1972). Tertiary beds in the valley have a gentle
eastward dip, and the thickness of basin-fill deposits is greater on the east
side than on the west.
A high-angle, normal fault (west side down) on the west flank of the Ruby
Range forms the eastern boundary of the Beaverhead valley (Figure 11-21). To
the north beyond the Alder valley, another northeast-trending fault runs along
the west flank of the Tobacco Root Mountains. Six miles west of Sheridan, the
basin's depth is over 8,000 feet (Petkewich, 1972). The Blacktail fault (north
side down) forms the southern boundary of the Beaverhead basin. This high-angle,
normal fault cuts Miocene beds, but has not moved since the beginning of the
Pliocene. Tertiary deposits thicken to 8,500 feet near the junction of this
fault and the Ruby Range fault. A high-angle, normal fault (south side down)
is inferred to be on the northeast border of the Melrose valley (Chandler, 1973;
Witkind, 1975). The Melrose valley is over 2,000 feet thick near its northeastern
boundary. On the south side of McCartney Mountain, the valley fill is over 3,000
feet thick. Along the sides of the Alder valley, Petkewich (1972) mapped three
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T2S
T3S
T4S
T5S
T6S
T7S
T8S
T9S
R11W
R10W
R9W
R8W
R7W
R6W
R5W
R4W
R3W
Isopach Interval; 1000 ft.
Map Scale: 1:500,000
Refer to basins no. 40 and 43
Isopach of Cenozoic fill in the Melsose and Beaverhead Valleys
Figure 11-21
- 81 -
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faults trending northwest-southeast. The graben has two faults parallel to
the south border of the Tobacco Root Mountains, each with south side downthrown,
and another fault (north side down) along the northeast border of the Ruby Range.
The Alder valley fill is over 4,000 feet thick near Alder.
Bedrock that outcrops along the basin's borders consists of Precambrian
metamorphic rocks, Paleozoic and Mesozoic sediments, Cretaceous-Tertiary intrusives
and early Tertiary volcanics. It is presumed that unconsolidated Tertiary deposits
of the Bozeman Group are underlain by rocks similar to those outcropping along
the mountain fronts. The lower portion of the Bozeman Group (the Renova Formation)
contains alternating limestones, mudstones, siltstones, sandstones, gravels and a
few conglomerates. Over 70 percent of the Renova Formation consists of very fine
or finer sediments. Deposition of the formation ended in middle Oligocene; an
episode of erosion that removed a large volume of Renova beds followed. Deposi-
tion of the upper part of the Bozeman Group, the Sixmile Creek Formation, began
in late Miocene and ended in middle to late Pliocene. Generally darker and
coarser than the Renova Formation, the Sixmile Creek Formation consists of 60
percent medium sand and coarser sediments, 20 percent fine to medium sand and
20 percent silt and finer sediments. Since the late Pliocene, an unknown amount
of Sixmile Creek strata has been eroded and a veneer of Quaternary deposits laid
down locally.
Within the Melrose and Beaverhead valleys are three distinct aquifer units:
Cretaceous to Precambrian bedrock; semiconsolidated Tertiary sediments; and
Quaternary alluvium. Fracture networks in the bedrock of the surrounding
mountains create a bedrock aquifer. This aquifer has only minor importance
because it is only capable of small yields and has limited access in the mountains.
Overlying the bedrock are Tertiary deposits primarily composed of fine-grained
silt, clay and some volcanic ash. This Tertiary aquifer probably has a large
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volume of ground water in storage, but because the aquifer contains so much
fine-grained material, the water cannot be released from storage. Therefore,
wells penetrating the Tertiary aquifer have low yields ranging between 5 and
10 gpm. The ground water from this aquifer is usually hard, and values for
dissolved solids average about 400 mg/L. The Tertiary sediments receive re-
charge principally from streams and irrigation water; probably very little direct
recharge to Tertiary deposits occurs from rainfall and snowmelt (Botz, 1967).
The alluvium bordering the Beaverhead River and its tributaries serves as
the most valuable aquifer in these valleys. It is composed of interlayered
gravels, sands, silts and clays and has a maximum total thickness of 200 feet
along the Beaverhead River (Botz, 1967). Yields of more than 900 gpm have been
obtained from this aquifer. The water is dominantly a calcium-magnesium
bicarbonate type, and because of this it is quite hard.
Recharge to the aquifer is from snowmelt runoff, rainfall and leakage from
the Tertiary sediments. Discharge occurs from evapotranspiration, wells and
springs and as base flow for the Beaverhead River during periods of low flow.
Madison Valley
The Madison valley is located west of the Madison Range, east of the
Gravelly Range and southeast of the Tobacco Root Mountains. Bedrock around the
valley includes Precambrian gneisses to the west and north and Precambrian dolo-
mite and schist to the southeast (Gary, 1980). Paleozoic and Mesozoic sedimentary
rocks outcrop northeast of the valley, and a Tertiary granitic intrusion is found
to the northwest in the Tobacco Root Mountains. To the southwest and south of
the Madison valley, Pliocene basalt and tuffs and Pleistocene tuff cover a large
area.
On the east side of the valley, the Madison fault (west side down) extends
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for 55 miles along the west flank of the Madison Range. Movement occurred
along this irregular north-trending fault in 1959. The fault block beneath the
Madison valley is tilted 5 to 10 degrees eastward into the Madison fault (Pardee,
1950) and maximum thickness of basin-fill strata is 9,000 feet along the east
side of the valley (Figure 11-22). Along the north side of the valley, another
fault (south side down) trends west-northwest and intersects the Madison fault.
In the upper Madison River valley, gravity data indicate a trough filled with
low-density material, such as basin-fill sediments, beneath the Tertiary volcanics
(Schofield, 1980). This trough is about 3,000 feet deep and extends from the
Madison valley to the Centennial valley. Detailed mapping in the area has shown
block faults (northwest side down) breaking the Tertiary volcanic rocks along
the southeast side of the trough (Gary, 1980).
Basin fill in the Madison valley consists mainly of unconsolidated con-
glomerate with rounded boulders and cobbles in a sandy, silty matrix and is late
Tertiary or early Pleistocene in age. Quaternary deposits include moraines,
landslides, fan deposits and glacial outwash. In the upper Madison valley,
Tertiary and Pleistocene sediments are interbedded with basalt flows and tuff
beds (Gary, 1980). In the lower Madison valley, however, the interbedded vol-
canics do not occur, and the Tertiary sequence becomes more like that in the
Three Forks basin—conglomerates and gravels with a large proportion of tuff-
aceous and fine-grained material and some interbedded sands.
The alluvium bordering the Madison River is the most prolific source of
ground water in the Madison valley. The alluvial deposits are comprised of
unconsolidated gravels, sands, silts and clays; however, a large percentage of
the finer-grained materials has been carried away by streamflow. The result is
a fairly well sorted deposit of coarse-grained sediments that have a high degree
of hydraulic conductivity. The thickness of the alluvium is quite variable and
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R2W R1W R1E R2E
Isopach Interval: 1000 ft.
Map Scale: 1:500,000
Refer to basin no. 47
Isopach of Cenozoic fill in the Madison Valley
Figure II-22
- 85 -
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may be as much as 100 feet thick near Jeffers. Well yields from this alluvial
aquifer generally average about 30 gpm, but the aquifer has the potential for
yields in excess of 100 gpm. Alluvial ground water is of good chemical quality,
suitable for domestic and stockwater uses.
Ground water is also derived from Tertiary sediments in the Madison valley.
Tertiary deposits are composed of a large percentage of fine-grained material
such as tuffaceous and clay-size sediments. These sediments inhibit the move-
ment of ground water and are the reason for the aquifer's relatively impermeable
nature. A well located in section 4, T. 11 S., R. IE., is reported to have a
transmissivity value of only 6,800 gallons per day per foot. This figure appears
to be fairly representative of these sediments. Wells drilled in Tertiary sedi-
ments usually range from 100 to 250 feet deep and have yields of 15 to 20 gpm,
but a number of deeper wells have yields greater than 50 gpm.
Geothermal waters occur near the town of Ennis. These springs issue from
a localized fault system there, and their hydrothermal potential is unknown.
Recharge to aquifers in the Madison valley is from influent streams, rain-
fall and snowmelt runoff. A small percentage also is derived from irrigation
return flows; however, the valley is used mainly for dryland farming. Evapo-
transpiration, effluent streams, springs and wells account for the ground-water
discharge in the valley. A comprehensive hydrogeologic study of the Madison
valley should be undertaken in order to evaluate the ground-water resources and
to determine the hydrochemistry of the system and the potential for development
of these resources.
Emigrant Valley
The easternmost intermontane basin in Montana, the Emigrant valley, lies
between the Gallatin Range on the west, the Snowy Mountains on the southeast
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and the Absaroka Range on the east. This basin began forming during the Miocene,
with movement along the Emigrant fault (west side down) and tilting of bedrock
and basin-fill strata to the east (Bonini and others, 1972). Seen along the
western flanks of the Absaroka Range and Snowy Mountains, this fault constitutes
the eastern limit of basin and range faulting in Montana (Reynolds, 1979).
Tertiary basin-fill deposits and the Tertiary volcanic bedrock of the basin floor
dip 10 to 20 degrees east into this fault. The combination of faulting and
tilting has resulted in a maximum basin-fill thickness of 3,000 feet and an
average thickness of 2,000 feet along the east side of the valley (Figure 11-23).
Movement along the fault has continued up to Holocene time, as shown by broken
Pleistocene deposits and hot springs aligned along the fault trace.
To the east of the valley, Precambrian metamorphic rocks predominate and
have been intruded by a few Tertiary granites. Paleozoic and Mesozoic sedimen-
tary rocks occur on both sides of the valley at its northern end and also outcrop
along the Mill Creek fault zone, an east-west trending fault which intersects the
Emigrant fault at Mill Creek. On the west side of the valley, Tertiary volcanics
conceal the Paleozoic and Mesozoic rocks that outcrop elsewhere in the Gallatin
Range (Bonini and others, 1972).
Late Miocene to early Pliocene deposits in the basin consist of tuffaceous
silts and clays with some interbedded sands and gravels. Above these deposits
are Pliocene stream gravels with well-rounded cobbles in a sandy matrix. In the
southern part of the Emigrant valley, late Tertiary basalts overlie the gravels.
Quaternary deposits in the valley consist of terrace deposits and glacial drift
(Horberg, 1940).
Ground water in the Emigrant valley is derived from a variety of geologic
sources. North of Pray, Montana, the valley floor is veneered with alluvial
deposits of the Yellowstone River. These deposits are of an unknown thickness
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T6E T7E T8E T9E T10E
Isopach Interval: 1000ft.
Map Scale: 1:500,000
Refer to basin no. 48
Isopach of Cenozoicfill in the Emigrant Valley
Figure 11-23
- 88 -
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and probably overlie similar till of Wisconsin age that is exposed in the side
canyons of the valley. The Yellowstone River alluvium is composed of a hetero-
geneous mixture of sand, gravel, silt and clay that readily yields water to wells.
The Montana Department of Fish, Wildlife and Parks has two campground wells in
section 28, T. 4 S., R. 9 E., that are completed in the alluvium. The wells
are 41 and 37 feet deep and have yields of 110 and 120 gpm, respectively.
General well yields for this aquifer range from 20 to 40 gpm.
South of Pray, Montana, the valley lowlands are principally ground moraine
of the Yellowstone Glacier of early to late Wisconsin age. These glacial deposits
are flanked by Tertiary terraces. The till is composed of a combination of
cobbles and gravels in a silty clay matrix. The Tertiary sediments are comprised
of interbedded fluvial sediments and tuffaceous deposits. Both the glacial till
and Tertiary deposits exhibit similar hydraulic properties and, for the most part,
can be considered as an aquifer unit. These deposits are semipermeable and, as
such, have a limited degree of hydraulic conductivity. Well yields are usually
small and average 5 to 15 gpm.
Ground water in the Emigrant valley is of good chemical quality and is used
for domestic, recreation and stockwater purposes. It is unknown if there are
sufficient yields for irrigation use, since no large-capacity wells (in excess
of 200 gpm) exist in the valley.
Recharge to the ground-water system is from precipitation and losses from
influent streams. Discharge occurs through evapotranspiration, effluent streams,
wells, springs and seeps.
Centennial Valley
Unlike the other intermontane basins of western Montana that trend north-
westerly, the Centennial valley trends east-west. Situated between the Cen-
tennial Mountains (south side) and the Snowcrest and Gravelly ranges (north side),
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the Centennial basin is more closely related to Snake River-Yellowstone Plateau
structures than to the basin-range faulting activity seen in the rest of south-
western Montana (Myers and Hamilton, 1964). The Centennial fault (north side
down) extends for 40 miles along the south side of the valley. From gravity
data, other faults (north sides down) are seen to parallel the Centennial fault
beneath the basin fill (Schofield, 1980). Across the valley, a series of faults
(south sides down) form the basin fill-bedrock contact. Gravity data indicate
more faults may parallel those beneath the valley sediments. In the center of
the valley, the basic graben structure is complicated by small northwest-trending
faults along the trough between the Madison and Centennial valleys (Schofield,
1980). Farther east, the Alaska basin, a small, roughly circular valley, is
bounded on its north, east and southwest sides by faults, each with the basin
side downthrown. This basin is rather deep for its size and is filled with about
3,000 feet of Cenozoic sediments. The Centennial valley contains a maximum of
7,000 feet of basin fill deposited over its irregularly faulted bedrock floor
(Figure 11-24).
Paleozoic and Mesozoic sedimentary rocks outcrop in the mountains north
and south of the Centennial valley and are overlain in places by abundant
Tertiary volcanics. Precambrian schist outcrops to the east around Alaska basin.
Cenozoic rocks in the Centennial valley consist of basalts, travertine and tuffs
interbedded with semiconsolidated and unconsolidated sediments. These sediments
include a middle Miocene channel sandstone and pebble-rich, poorly sorted sand-
stone, a Miocene freshwater limestone, alluvial-fan deposits and colluvium,
glacial outwash, silts and sands with local interbedded gravels and dune sand
(Sonderegger and others, 1980; Honkala, 1949).
To date, there exists a paucity of ground-water data concerning both shallow
and deep aquifers in the Centennial valley. A review of wells drilled in the
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R2W R1W R1E R2E R3E
Isopach Interval: 1000 ft,
Map Scale: 1:500,000
Refer to basin no. 51
Isopach of Cenozoic fill in the Centennial Valley
Figure 11 -24
-------
valley found only a few well logs recorded for the area. The wells generally
ranged between 50 and 100 feet deep and had yields of 15 to 30 gpm. These wells
probably obtain their water from a number of hydrogeologic units in the valley.
Most of the valley floor is mantled with a veneer of Quaternary alluvial
deposits. They are composed of a heterogeneous mixture of gravel, sand, silt
and clay of unknown thickness. The northern portion of the valley has been
surficially mapped as dune sand, conglomerate and tuffaceous deposits. These
deposits normally produce limited amounts of ground water, and it is assumed
that their potential yields are 5 to 10 gpm. Ground water is used only for
domestic supply and stockwater wells, since large-capacity irrigation wells are
nonexistent. The upper 1,000 feet of valley-fill materials probably have an
effective porosity of at least 15 percent; thus, the ground water in storage
in this zone amounts to about 150 acre-feet per acre (Sonderegger, 1982). Dis-
solved-solids concentrations in the water are generally less than 400 mg/L, and
the water is thus suitable for domestic use.
Underlying the Quaternary deposits are interbedded Tertiary sediments and
basalt and rhyolite flows. Tertiary sediments have been previously described,
and their potential as a ground-water resource is unknown since wells of
sufficient depth to penetrate them have not been drilled. There also exist a
number of thermal springs in the Centennial valley. Possible heat sources for
these springs could be either an intrusive body or deep circulation of water
along fractures.
The main source of recharge for the aquifers in the valley is rainfall and
snowmelt runoff and, to some extent, return flow from surface-water irrigation.
Ground-water discharge occurs as springs, seeps and wells and is accompanied by
evapotranspiration and effluent streamflow. A thorough ground-water resource
evaluation should be made for the Centennial valley.
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CONSOLIDATED SEDIMENTARY ROCKS
Consolidated sedimentary rocks in the Rocky Mountains region represent all
geologic time periods from Precambrian through Cretaceous, except the Silurian,
(see Figure II-4 for a stratigraphic time scale). These formations have been
faulted, folded and occasionally overturned throughout various orogenic episodes.
Because individual formations are frequently structurally separated and dis-
continuous, this entire stratigraphic section is considered a single aquifer
system for the ease of evaluation and interpretation. Depositional environments
for individual formations have been discussed in section C.l. of this report.
The Precambrian formations, comprising most of the northern half of the
Rocky Mountains region, consist of red and green argillites with intervening
black, maroon and pink quartzites. There are 15,000 to perhaps as much as
45,000 feet of Precambrian sediments deposited in this portion of the Rocky
Mountains region. These sediments are roughly 0.8 to 1.4 billion years old and
are collectively known as the Belt Supergroup. The yield from wells completed
in Precambrian rocks is variable but generally small, because these rocks are
"tight" and water must be obtained from secondary openings such as joints,
fractures, faults and weathered zones of the bedrock. Yields range from 1 to
35 gpm, with 10 gpm being about average. Water quality from Precambrian sediments
is very good, the water usually having less than 300 mg/L of dissolved solids.
Paleozoic strata are made up primarily of carbonate sediments and shales,
with some clastic formations such as the Flathead and Quadrant formations at the
base and the top of the section, respectively. Mountain-forming stresses have
warped and bent the formations into a series of folds and thrust sheets. As in
the Creat Plains region, the Madison Formation is important not only as a source
of ground water but as a place for recharge infiltration. Well yields from
Paleozoic strata are highly variable and are dependent not only on the formation
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to which the well is drilled but also on the proximity to outcropping of the
formation. Water quality is generally good but can vary, depending on the
formation drilled, depth and distance from the recharge area. Wells completed
in Paleozoic sediments are used primarily for domestic and stockwater purposes,
although some larger-capacity wells in the Madison Formation are used for
irrigation.
Mesozoic strata demonstrate a gradual transition from the chiefly marine
beds of the lower formations to mostly terrestrial sediments found in the upper
part of the section. These formations have also been subjected to the same
tectonic stresses that deformed the underlying Paleozoic sediments. Deforma-
tion has not only folded, inclined and overturned the strata, but often displaced
beds vertically and laterally hundreds to tens of thousands of feet. The major
water-bearing units (aquifers) within the Mesozoic system are the Jurassic
Swift Sandstone, the basal Cretaceous Kootenai Sandstone and the Eagle Sandstone
where erosion has not removed it. Impermeable shale formations are interbedded
among the sandstone units and act as confining beds. Faulting, however, has
often juxtaposed different formations, and the extent to which the aquifers are
hydraulically interconnected is uncertain. There exists practically no water-
quality data for wells drilled in Mesozoic formations of the Rocky Mountains
region, but moderate values of dissolved solids would be expected. Well yields
for these aquifers are widely variable, ranging from 5 to 100 gpm, and are con-
tingent upon location, attitude of the bedded rocks and proximity to recharge
areas. Rainfall and snowmelt water account for nearly all of the recharge for
"consolidated sedimentary rocks." Evapotranspiration from dense forests, springs
and wells discharge the ground water to keep the system in balance.
The aforementioned Precambrian, Paleozoic and Mesozoic strata comprise all
of the mountain ranges north of the "batholithic province" and a substantial
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number of scattered ranges in the central and southern portions of the Rocky
Mountains region. The inaccessibility of the mountain ranges has deterred or
prevented development and drilling, thereby resulting in scant ground-water
information for this aquifer unit.
METAMORPHIC AND IGNEOUS ROCKS
Metamorphic and igneous rocks comprise a large area of the south-central
portion of the Rocky Mountains region. The Boulder and Idaho batholiths of
Cretaceous age are the largest plutons, while others such as the Tobacco Root,
Pioneer and Flint Creek stocks are of lesser areal extent. These batholiths
and their associated contact metamorphic assemblages outcrop or underlie most
of this central portion and frequently are referred to as the "batholithic
province." The plutons are composed mainly of quartz monzonite and related
granitic rocks.
The availability of ground water from granite is rather limited. Water
availability from this type of crystalline rock is entirely dependent upon
secondary porosity because of insufficient primary porosity. Water from these
rocks must be obtained from secondary porosity, which is produced by horizontal
pressure release fractures that form as a result of sheet unloading; vertical
joint sets that were produced from tension release fracturing; and faults that
were a result of tectonic stresses. The combined interconnectedness of these
openings provide space for ground-water storage and conduits for movement.
These features are often surficially expressed as lineaments and joint traces,
and most of the higher-yield wells are located where the fractures intersect.
The wells are generally between 100 and 200 feet deep, because permeability
generally decreases with depth. Average well yields for granitic rocks are
approximately 2 to 5 gpm. There is a paucity of water-quality data from igneous
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rocks, but values of 300 mg/L of dissolved solids are common.
Proximal to these large batholiths and stocks are various Cretaceous and
Tertiary extrusive rocks. The Elkhorn Mountain and Lowland Creek volcanics
outcrop over considerable areas and are composed mainly of rhyolites and latites.
These rocks are a source of potable water for many rural families. Wells from
extrusive rocks generally have low yields because of their dependence on
fracture openings. This aquifer is mainly recharged from precipitation, and
wells and springs are the primary sources of discharge.
Lying south and east of the batholithic province is an extensive area that
contains pre-Belt metamorphic rocks (2.7 to 1.7 billion years old). The Bear-
tooth and Ruby ranges and part of the Tobacco Root Mountains are composed of
this metamorphic assemblage. They are mainly granitic gneisses and schists
that have been fractured enough to allow ground-water storage. Well yields tend
to be very small, but water quality is good (though the water often has some
iron concentrations). These rocks are therefore an important domestic source of
ground water in the southern portions of the Rocky Mountains region. Recharge
and discharge for this aquifer are also through precipitation and wells and
springs, respectively.
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III. GROUND-WATER USE
Information on water use in Montana prior to 1980 is extremely limited,
because accurate data on withdrawal rates are practically nonexistent. Com-
munities have the best opportunity to record water use, but in most instances
only new delivery systems are equipped to measure discharge. Similarly, rural,
agricultural and industrial water users often have no means of measurement, and
only estimates can be made for those values. Montana is presently quantifying
its water use and consumption, however, through a water-right adjudication
program. This program is being implemented through the Department of Natural
Resources and Conservation under Senate Bill No. 76. All water-use applications
are to be filed by April 30, 1982, and will then be reviewed and summarized.
Better estimates of ground-water and surface-water use will become available
after that date. The department is also compiling a 1980 water-use and quanti-
fication survey, which is yet to be released.
Major uses of ground water in the Rocky Mountains region are for irrigation,
municipalities, industry, rural-domestic and livestock. Table II-4 summarizes,
by county, the various well uses of this region. Most of these wells are com-
pleted in the Quaternary alluvial or glacial aquifers, although Tertiary and
bedrock aquifers are exploited locally. An estimate of the cumulative ground
water withdrawn from the Rocky Mountains region is approximately 146.14 million
gallons per day (mgd) or 448.65 acre-feet per day. This value for ground water
withdrawn represents about 3 percent of the total amount of water diverted
within the Rocky Mountains region, a figure that is believed to be a conservative
estimate. Even though present ground-water use is small, it is the only viable
source of potable water that can and will be further developed now that surface-
water supplies are over appropriated in this region.
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TABLE 11—4
WELL USE BY COUNTY, ROCKY MOUNTAINS REGION
August 1981
COUNTY
COM
DOM
D+S
IRR
IND
PUB
STK
MU
OTH
NOT
RPT
TOTAL
Beaverhead
1 1
663
168
42
4
14
258
33
30
6
1249
Broadwater
0
308
145
43
1
8
191
33
28
1
758
Deerlodge
3
532
59
16
6
4
23
22
14
2
681
Flathead
19
2631
696
81
37
34
41
233
82
8
3862
Gallatin
15
2101
568
48
18
27
189
95
95
2
3158
Glacier
8
130
153
1
20
4
104
10
10
0
440
Granite
4
348
72
9
1
4
36
13
30
0
517
Jefferson
1
556
90
15
6
25
85
46
23
1
848
Lake
2
885
437
18
3
20
52
94
26
2
1539
Lewis and Clark
10
2121
297
67
15
36
149
135
142
4
2976
Lincoln
11
1091
89
7
6
15
14
31
39
2
1305
Madison
2
685
219
18
3
14
158
26
28
0
1153
Meagher
0
87
63
1
2
5
53
20
11
2
244
Mineral
5
210
25
6
3
8
6
12
18
2
295
Missoula
14
2354
292
47
65
60
47
153
103
48
3183
Park
1
564
183
25
9
11
65
57
36
10
961
Powell
1
363
100
15
3
6
71
28
8
2
597
Ravalli
10
3338
348
193
18
30
95
550
481
2
5065
Sanders
5
479
193
61
2
8
43
80
27
1
899
Silver Bow
5
552
58
28
10
4
28
22
23
2
732
To tal
127
19998
4255
741
232
337
1708
1713
1254
97
30462
COM-Community; DOM-
Stockwater only;
-Domestic; D+S
MU-Multiuse;
-Domestic
OTH-Other;
and Stockwater; IRR-Irrigation;
; NOTRPT-Not Reported.
IND-Industrial; PUB-
-Public;
STK-
-------
AGRICULTURE
Agriculture, specifically crop irrigation and livestock watering, uses the
largest amount of ground water in the Rocky Mountains region. Tertiary uses
that are agriculturally oriented include fish farming and wildlife refuges.
Irrigation
There are approximately 1,244,000 acres of irrigated land in the Rocky
Mountains region. Most of the irrigated cropland in the region is hayland,
while small grains and potatoes account for a substantial portion of the
remainder. Other crops in the region dependent upon irrigation are sweet and
tart cherry orchards, tree farms and mint plantations. The percentage of this
acreage that is irrigated in any given year is uncertain. Roughly 4.89 billion
gallons per day (bgjd) are diverted for this acreage, of which 1 percent is with-
drawn from ground-water sources. Almost all irrigation wells are completed in
the unconsolidated alluvial aquifer, but a few other large-capacity wells obtain
water from Tertiary aquifers.
Requirements for diversion are more than double the consumptive use,
resulting in a return flow that is 53 percent of the total diversion (DNRC,
1974). Consumptive use varies with irrigation efficiency, rates of application
and other factors such as the crop, soil, precipitation, growing season and
ambient temperature. Nearly all irrigation is used for raising feed crops to
support the livestock industry.
Livestock
Stock consumptive use of ground water in the Rocky Mountains region is
estimated to be 8.5 mgd, of which 5 percent is withdrawn from ground-water
sources. Cattle and sheep account for most of the water consumed, with average
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daily consumption values of 15 and 3 gallons per head per day, respectively.
Pigs, horses and other livestock use the remainder of stockwater that is consumed.
About 1,700 wells are used for stockwatering only, and another 4,300 rural
wells are used jointly for domestic and stockwater purposes. Most stockwater
wells derive ground water from the alluvial aquifers; Tertiary and bedrock
aquifers also offer viable sources for sufficient amounts of ground water.
Springs and seeps are another source for stockwater within the region, but are
not well identified because their source and discharge rate are often unknown.
Typical stock wells and springs usually have sustained yields of 10 to 15 gpm.
Stockwater wells are an integral part of the livestock ranching industry within
the Rocky Mountains region.
Aquaculture is a new and increasingly popular aspect of the agricultural
industry. Many privately owned fish farms have recently begun operations in
this region. Although these businesses use ground water nonconsumptively, they
rely totally on springs and wells to maintain their livelihood. State-owned
fish hatcheries are also dependent upon ground-water sources in much the same way.
MUNICIPAL AND DOMESTIC
A computer listing produced by the Montana Department of Health and
Environmental Services in 1980 showed that there were 65 communities in the
Rocky Mountains region of Montana that have municipal water-supply systems. The
total number of public supply systems in this region is about 330 if trailer
courts, nursing homes and other institutional systems are included. Of the 65
communities, 16 rely exclusively on surface water; another 16 use both surface
and ground water; and the remaining 33 communities depend solely on wells or
springs for their water supply. Of the 393,625 people who reside within the
Rocky Mountains region of Montana, approximatley 259,700 live in municipalities.
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Of these, 93,070 depend exclusively upon ground water for their drinking and
household needs; they withdraw a total of about 30.01 million gallons of water
per day.
Quaternary alluvium is the primary aquifer used for municipal wells in
the Rocky Mountains region, supplying, perhaps, as much as 70 percent of the
water withdrawn. Tertiary and glacial deposits provide most of the remainder.
The quality of water used by most of the communities in the Rocky Mountains
region of Montana is generally excellent, and all systems tested had fewer dis-
solved solids than the maximum recommended by the Environmental Protection Agency.
Iron is sometimes a problem in trailer-court water supplies; as an example,
Wilsall had a concentration of 2.9 mg/L of iron in its water supply. Several
water systems had measureable trace elements in the water they supplied. The
highest lead value was 0.18 mg/L in water from a trailer court near Big Sky.
Arsenic measured 0.6 mg/L in water supplied by Three Forks, and mercury was
highest near West Glacier and Coram, 0.33 and 0.35 mg/L, respectively. Most
community water supplies had low nitrate values. Water from the supply system
at Alberton, however, had 4.4 mg/L; White Sulphur Springs had 4.8 mg/L; and
Wilsall had 11.8 mg/L. Many trailer courts had nitrates exceeding 5.0 mg/L
in their water supplies.
Domestic water is that ground water used by all persons not served by a
municipal or community water system. For the most part, domestic wells primarily
are used by rural residents, although many subdivision units also have individual
wells. The approximately 20,000 domestic wells comprise the largest single
category (65%) of permitted wells in the Rocky Mountains region. It is estimated
that an average withdrawal of 33.86 million gallons is consumed daily in the
Rocky Mountains region.
Because most residential settlements are within valleys, the Quaternary
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alluvial aquifer is the primary ground-water source. An example of this is the
Gallatin Valley, where new subdivisions with their accompanying wells are being
constructed throughout the valley. The Tertiary aquifer is also an important
source of ground water for many rural residents, as in the Bitterroot Valley;
the Sunset Bench subdivision obtains its potable supply from this aquifer. As
evidenced by the large percentage of domestic wells, ground water is dominantly
relied on for rural consumption.
INDUSTRY
The Montana Department of Natural Resources and Conservation defines self-
supplied industrial water as that which is obtained from a source of supply by
industry, as opposed to that provided by a municipality. An industry is also
considered to be self-supplied if any of the water it uses is obtained from its
privately owned water-supply facilities.
It is estimated that 28 mgd of ground water are withdrawn for industrial
use in the Rocky Mountains region, of which 30 percent is consumed. The water
that is not consumed is either discharged as surface-water flow, or treated and
recycled for reuse or disposed of through injection wells.
Industrial water use in the Rocky Mountains region is dominated by the
minerals industry. The Anaconda Minerals Company operations at Butte and
Columbia Falls account for a major portion of the ground water withdrawn in the
region. The Butte operation withdraws roughly 7.5 mgd for mine dewatering and
processing the copper ore. Much of this water is recycled, and the exact amount
consumed is unknown as it is dependent upon daily operations. The Anaconda
Aluminum Plant at Columbia Falls withdraws approximately 4.63 mgd, of which 0.18
mgd are consumed for either refining or cooling uses. Another mineral industry
that withdraws large quantities of ground water is the Stauffer Chemical Company.
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One million gallons per day are withdrawn for its phosphate-processing operations,
of which one-fourth is consumed. The remaining minerals-processing industries
use very small amounts of water.
Other large industrial water users include the Horner-Waldorf pulp mill and
the White Pine Sash Company of Missoula. Horner-Waldorf has an intake rate of
16 mgd, of which 15 percent is consumed, whereas the White Pine Sash Company is
estimated to consume 0.14 mdg as steam.
Lesser amounts of ground water are withdrawn also for a variety of other
uses such as geothermal heating, sanitation and boiler feeding.
Of the total amount of water diverted for industry in the Rocky Mountains
region, about 40 percent is ground water. Most industrial wells tap the Quat-
ernary alluvial aquifer; however, some obtain water from Pleistocene glacial
deposits. Both of these aquifers are a prolific source of good-quality water
for industrial use.
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IV. WATER QUALITY
Data sources
More than 3,000 water-quality analyses contained in the computer files at
the Montana Bureau of Mines and Geology (MBMG) were reviewed for the UIC Project;
approximately 375 of these analyses are from the Rocky Mountains region. Addi-
tional analyses are contained in MBMG and U.S. Geological Survey (USGS) bulletins,
memoirs, open-file reports, professional papers and unpublished reports.
The MBMG water-quality file contains water-quality analyses generated by
the MBMG Analytical Division. Primary customers of this division are the MBMG
Hydrology Division, the USGS Water Resources Division in Helena, Montana, and
the U.S. Forest Service (USFS). The USGS and MBMG Hydrology Division furnish
water samples taken from ground-water sources within the State of Montana to
the MBMG laboratory for analysis; the results of these analyses have become part
of an integrated data bank.
Previously published geologic and hydrologic reports for the intermontane
basins of the Rocky Mountains region contain water-quality analyses. The most
recent USGS publication, Open-File Report 80-1102, by Moreland and Leonard (1980),
discussed ground-water characteristics of the Helena valley. The water-quality
data contained in this report were porcessed at the MBMG laboratory during 1979
and 1980 and are contained in the listing of water-quality data in Appendix E.
Older reports—including those written by Coffin and others (1971) on the Tobacco
and Upper Stillwater valleys; Hackett and others (1960) on the Gallatin valley;
Konizeski and others (1968) on the Kalispell valley; McMurtrey and others (1972)
on the Bitterroot valley; and McMurtrey and others (1965) on the Missoula basin—
contain water-quality analyses and descriptions of ground water for their
respective areas. An ongoing project at the MBMG is to assimilate these previously
published analyses in the data-management system.
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Appendix E contains a tabulation of those analyses in the water-quality
system selected for this project. The analyses have been sorted by formation
or aquifer and by township, range and section; many have been plotted on the
"Dissolved Solids Map series" included with this report. Occasionally, points
will appear on the listings that have not been plotted on the maps, and con-
versely, points will appear on the maps that are not contained in the tabulation.
This has occurred because much previously published data are not computerized,
and because the listings may include data created since the compilation of the
maps.
General water quality
Water-quality data of ground water for three aquifer groups in the Rocky
Mountains region were extrateed. These aquifers include 1) Cenozoic basin-fill
deposits; 2) early Tertiary through Precambrian consolidated sedimentary rocks;
and 3) igneous and metamorphic rocks.
Table II-5 compares selected elements and ions to drinking-water-quality
standards published by the U.S. Environmental Protection Agency (EPA). Since
no standard has been established for sodium plus potassium, however, an arbitrary
value of 250 mg/L has been selected as a reference point.
Based on these data, ground water in the Rocky Mountains region is generally
of better quality than that recommended by the EPA's standards. In the three
aquifer groups, 97 percent of the samples had dissolved-solids concentrations of
less than 500 mg/L. Less than 1 percent of the samples had nitrate (as N) con-
centrations greater than 10 mg/L; approximately 99 percent of the analyses reported
sulfate concentrations of less than 250 mg/L; approximately 99 percent of the
analyses reported sulfate concentrations of less than 250 mg/L; and there were no
chloride concentrations greater than 250 mg/L. Manganese and iron are the two
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TABLE II-5
COMPARISON OF SELECTED ELEMENTS AND IONS IN WATERS OF THE ROCKY
MOUNTAINS REGION, MONTANA, TO DRINKING-WATER-QUALITY STANDARDS4
AQUIFER
CONSTITUENTS
NUMBER OF
% GREATER
% LESS THAN
AVERAGE
AND
VALUES
THAN STANDARD
STANDARD
CONCENTRA"!
STANDARDS
REPORTED
IN MG/L
Cenozoic basin-fill
Na+K(250)1
305
< 1
> 99
33.
deposits
Fe(.3)2
304
12
88
.3
Mn(.05)2
305
23
77
.09
Cl(250)2
305
< 1
> 99
11.
S04(250)2
305
3
97
.44
N(10)3
304
< 1
> 99
1.
Ds(500)2
305
7
93
264.
Early Tertiary through
Na+K(250)1
27
4
96
83.
PreCambrian
Fe(.3)
27
11
89
.1
consolidated
Mn(.05)2
27
7
93
.017
sediments
CI(250)2
27
0
100
13.
S04(250)2
27
0
100
59.
N(10)3
27
0
100
.4
Ds(500)2
27
0
100
316.
Igneous and
Na+K(250)1
42
0
100
21.
metamorphic rocks
Fe(.3)2
42
5
95
.1
Mn(.05)
42
12
88
.032
CI(250)2
42
0
100
7.
SO,(250)2
42
0
100
30.
N(TO)3
42
0
100
.5
Ds(500)2
42
2
98
195.
^ No standard has been set.
A concentration
of 250 mg/L has been selected
as a point of
reference.
2
Secondary drinking-water
standard in mg/L.
Primary drinking-water standard in mg/L.
Source: U.S. Environmental Protection Agency, 1976.
-------
most likely elements to exceed the water-quality standards, with 13 percent
and 9 percent of the reported values, respectively, being greater than the
standards. In some areas, such as unconsolidated sediments in the Bitterroot
Valley, dissolved iron concentrations commonly exceed .3 mg/L and often are
several mg/L. In areas such as these, iron staining of household fixtures and
clothing are common.
Cenozoic basin-fill deposits
Most of the 305 analyses in this group are for ground water from uncon-
solidated to semiconsolidated, Holocene to Tertiary sediments deposited in the
intermontane basins. The geographic distribution of these data is uneven
because certain locales, such as the Helena valley or the Little Bitterroot
valley have been sampled extensively during MBMG or USGS projects, and other
areas, such as the Beaverhead valley, have had only a few water samples collected.
Dissolved solids in the Cenozoic basin-fill and alluvial deposits range
from a high of 1,273 mg/L for water from a 1,498-foot-deep geothermal test well
producing water from Tertiary sediments at the Warm Springs State Hospital in
T. 5 N., R. 10 W., sec. 13DCC in Deer Lodge County, to a low of 27 mg/L for
water from a USGS research well completed in glacial deposits in T. 28 N.,
R. 33 W., sec. 9BDDB in Sanders County near Libby. The average dissolved solids
for all analyses from this group are 260 mg/L.
Figure 11-25 is a plot of dissolved solids versus the number of occurrences
for the samples in that group. The majority of the analyses plotted represent
calcium bicarbonate type, but some sodium bicarbonate-type waters occur in almost
every dissolved-solids range. The lowest dissolved-solids value in the group is
for a calcium bicarbonate water, while the highest reported dissolved-solids
value is for a calcium sulfate-type water.
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15-
350 400
DISSOLVED SOLIDS IN MC/L
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Numerous older analyses exist for basin-fill and unconsolidated alluvial
deposits in the Rocky Mountains region. Coffin and others (1971) reported that
waters in the Tobacco and Upper Stillwater valleys of northwestern Montana
range between 80 to 1,500 mg/L of dissolved solids. The waters are generally
calcium bicarbonate-type, and iron concentrations range from below the detection
limit to .07 mg/L, occasionally causing problems. Based on 58 analyses, Hackett
and others (1960) reported that waters in the Gallatin Valley are predominantly
calcium bicarbonate-type and range from 154 to 597 mg/L of dissolved solids.
Konizeski and others (1968) reported that Quaternary aquifers in the Kalispell
Valley produce water ranging between 132 to 788 mg/L in dissolved solids. Water
types are generally calcium bicarbonate, but iron concentrations as high as
14.1 mg/L are reported. McMurtrey and others (1965), in discussing the hydrology
of the Missoula basin, reported dissolved-solids concentrations ranging from 94
to 326 mg/L. Iron concentrations range from .04 to 6.9 mg/L. Calcium and
bicarbonate are generally the most common cation and anion present. McMurtrey
and otehrs (1972) reported dissolved-solids concentrations for the Bitterroot
Valley south of Missoula ranging from 42 to 748 mg/L. Iron concentrations
range from .01 to 4.1 mg/L and can cause problems by staining clothing and
household fixtures. Dissolved-solids concentrations along the west side of the
valley commonly are lower than those for the east side, because the granitic
rocks to the west contain fewer soluble minerals than the sedimentary and
igneous rocks to the east. Moreland and Leonard (1980) described the qualities
and types of ground water for the Helena Valley. These waters are generally
calcium bicarbonate-type and range in dissolved solids from 111 to 936 mg/L,
with an approximate average of 330 mg/L. Anomalous samples from T. 10 N.,
R. 3 W., sections 16, 17 and 18, show evidence of poor sewage-disposal practices
and/or leachate from a landfill.
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Early Tertiary through Precambrian consolidated sedimentary rocks
There are only 20 analyses recorded for ground water from early Tertiary
through Precambrian consolidated rocks in the MBMG data system. The average
value of dissolved solids for these samples is 316 mg/L. A major reason for
the small number of analyses is that relatively few people live in areas under-
lain by these materials, resulting in few wells. Most of the ground water
development in the Rocky Mountains region has occurred in the intermontane
basins and stream valleys, where water is obtained from basin-fill deposits or
alluvium. Dissolved-solids concentrations range from 481 mg/L for water from
McMenomy warm springs in T. 9 S., R. 10 W., sec. 29AAAC in Beaverhead County,
to 106 mg/L for water from a spring in T. 4 S., R. 13 E., sec. 5ADCB in Sweet
Grass County. Both of these springs represent discharge from Madison Group
rocks but illustrate differing circulation regimes. The waters from the McMenomy
spring that are higher in dissolved solids come from a deep circulation system,
accounting for the calcium sulfate character and relatively warm temperature
(19°C) of the water. The water from the spring in Sweet Grass County that is
lower in dissolved solids is a calcium bicarbonate type and is from a shallow
circulation system in the Madison group.
Figure 11-26 is a plot of dissolved solids versus the number of occurrences
for ground water from late Tertiary through Precambrian consolidated sedimentary
rocks. As can be seen from the patterns representing water types, calcium bi-
carbonate waters are most common, followed by sodium bicarbonate waters.
Igneous and metamorphic rocks
There are 42 analyses of water from igneous and metamorphic rocks that
also represent portions of the Rocky Mountains region where relatively little
ground-water development has taken place. Dissolved-solids concentrations
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FIGURE 11-26—FREQUENCY OF OCCURRENCE VERSUS
DISSOLVED SOLIDS FOR WATERS FROM EARLY TERTIARY
THROUGH PRECAMBRIAN CONSOLIDATED ROCKS, ROCKY
MOUNTAINS REGION, MONTANA.
CaHCO.
NaHCO,
OTHERS
NaSO.
A
NaC03
CaSO,
-8
451_ » >501
500
DISSOLVED SOLIDS IN MG/L
- Ill -
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average 195 mg/L and range from a high of 672 mg/L in water from a 6,970-foot
geothermal test well in T. 12 N., R. 6 W., sec. 32ABD near Marysville in Lewis
and Clark County, to a low of 28 mg/L in water from a spring in T. 13 S.,
R. 2 E., sec. 31CADD in the Centennial Valley in Beaverhead County. The water
that is higher in dissolved solids from the geothermal test well is a sodium
bicarbonate sulfate-type produced by plutonic rocks and indicates a deep, warm-
water circulation system. The water that is lower in dissolved solids is a
calcium bicarbonate-type and is discharged from metamorphic rocks.
Figure 11-27 is a plot of dissolved solids versus the number of occurrences
for ground water from igneous and metamorphic sources. As can be seen from the
patterns representing the various water types, the majority of the analyses are
for calcium bicarbonate-type waters.
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200 250 300 350
DISSOLVED SOLIDS IN MC/L
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V. SUMMARY
1. Four major aquifer systems have been identified within the Rocky
Mountains region of Montana. These are the Quaternary unconsolidated deposits;
the Tertiary valley-fill sediments; consolidated sedimentary rocks; and meta-
morphic and igneous rocks. Dissolved solids maps have been prepared for each
of these aquifer units and thickness maps (isopachs) were generated for most
of the Tertiary basins within the Rocky Mountains region. Although considerable
research has been completed to compile these maps, other parameters such as
recharge rates, ground-water flow paths, the extent of interformational mixing
and values for transmissivity and storativity are poorly known. Other data
pertaining to the hydrochemical aspects of the formations are sparse, but are
continually being accumulated.
2. Quaternary unconsolidated aquifers include: alluvium, colluvium,
terrace deposits, glacial deposits, high level gravels and the deeply weathered
surface of some sedimentary formations. Unconsolidated deposits are composed
of uncompacted gravels, sands, silts and clays which can be either sorted or
unsorted. Well yields are highly variable, ranging from a few gpm to in excess
of 1,000 gpm, depending upon location. Development of these aquifers for
drinking water, irrigation and stock uses has been extensive because shallow
drilling depths allow for an easily accessible water source. Recharge to
Quaternary unconsolidated deposits takes place through direct infiltration of
precipitation streamflow loss, upward leakage from underlying bedrock units
and irrigation return-flow.
Ground water derived from unconsolidated deposits is generally of excellent
water quality; dissolved solids concentrations usually average between 350 and
450 mg/L.
3. Tertiary-age sediments comprise the major thickness of basin-fill
deposits found in western Montana's intermontane valleys. Although two numerous
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formations are recognized, it appears detritus from the surrounding mountains
infilled the basins under similar climatic conditions, but different drainage
systems and varied catastrophic events account for the different lithologies.
Typical lithologies include interbedded sandstones, channel conglomerates,
tuffs and siltstones. Because of the coarse-grained nature of these formations,
they are a viable source for ground water.
Wells penetrating Tertiary-age sediments generally have yields of 5 to 25
gpm, but can be in excess of 1,000 gpm depending upon location.
Values for transmissivity and storativity for these sediments are generally
unknown because only a few wells have been aquifer tested. Wells completed in
Tertiary sediments are drilled to varying depths, but usually are greater than
100 feet d'eep. The water quality averages around 500 mg/L of dissolved solids
and is suitable for domestic, stockwater and irrigation uses.
4. Consolidated sedimentary rocks in the Rocky Mountains region represent,
excepting the Silurian, all geologic time periods from Precambrian through
Cretaceous. These formations have been faulted, folded and occasionally over-
turned throughout various orogenic intervals. Because individual formations
are frequently structurally separated and discontinuous, this entire strati-
graphic section is considered a single aquifer package for the ease of evaluation
and interpretation.
Well yields are highly variable and although they are generally low,
averaging 5 to 10 gpm. The water quality of these sedimentary rocks is usually
good and suitable for all types of uses.
5. Metamorphic and igneous rocks comprise a large area of the south-central
portion of the Rocky Mountains region. The Boulder and Idaho batholiths of
Cretaceous age are the largest plutons, while associated volcanic rocks occupy
a lesser areal extent.
The availability of ground water from granite and volcanic rocks is rather
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limited and dependent upon the amount of secondary porosity present. Average
well yields are usually less than 5 gpm of good quality water.
6. A precise tabulation of ground-water use by economic sector and aquifer
source is limited by the lack of accurate withdrawal-rate data, and for this
reason figures presented in this report are estimates of water use. However,
Montana is presently quantifying its water use and consumption through the water-
right adjudication program. Both surface- and ground-water claims shall be filed
prior to April 30, 1982, and will be adjudicated after that date. Upon completion
of the adjudication filings, the State will possess a written record of all water
rights quantified according to time and volume of use.
Municipal ground-water use totals 30.01 million gallons of ground water per
day. Slightly more than one-half (51 percent) of the communities of the Rocky
Mountains region rely solely upon ground water for their drinking and household
needs. Estimates show that approximately 70 percent of these water supplies
derive their water from alluvium or unconsolidated deposits.
Current estimates indicate that ground-water supplies approximately three
percent (448.65 acre-feet per day) of the water used in the Rocky Mountains region.
Agriculture is the largest ground-water user within the region, mainly for irriga-
tion needs. Roughly 4.89 bgd are diverted for irrigation, of which one percent
is withdrawn from ground-water sources.
Domestic water is that which is used by people not served by a community
system, usually rural residents. There are approximately 20,000 domestic and
stockwater wells in the Rocky Mountains region providing 95 percent of the rural
population with a potable supply.
The mineral industry is the largest commercial user of ground water in this
region. Industrial uses of ground water consist of processing ore and mine de-
watering. Of the total amount of water diverted for industry in this region,
about 40 percent is ground water.
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VI. REFERENCES CITED
Alden, W.C., 1953, Physiography and glacial geology of western Montana and
adjacent areas: U.S. Geological Survey Professional Paper 231, 200 p.
Alexander, R.G., Jr., 1955, Geology of the Whitehall area, Montana: Yellow-
stone-Bighorn Research Association, Inc., Yellowstone-Bighorn Research Project
Contribution 195, 111 p.
Bingler, E.C. and Stickney, M.C., 1981, Earthquake hazard evaluation of the
Helena valley area, Montana: Montana Bureau of Mines and Geology Open-File
Report 83, 30 p.
Boettcher, A.J. and Gosling, A.W., 1977, Water resources of the Clark Fork Basin
upstream from St. Regis, Montana: Montana Bureau of Mines and Geology
Bulletin 104.
Boettcher, A.J., 1980, Ground-water resources in the central part of the Flathead
Indian Reservation, northwestern Montana: USGS Open-File Report 80-731, 41 p.
Bonini, Kelley, Hughes, "Gravity STudies of the Crazy Mountains and the West
Flank of the Beartooth Mountains, Montana": Montana Geological Society, 21st
Annual Field Conference, Sept. 1972.
Bonini, W.E., Kelley, W.N., Jr., and Hughes, D.W., 1972, Gravity studies of the
Crazy Mountains and the west flank of the Beartooth Mountains, Montana, in
Crazy Mountains basin: Montana Geological Society Guidebook, 21st Annual
Field Conference, September 1972, p. 119-127.
Bonini, W.E. and Smith, R.B., 1974, Bouguer gravity map of Montana: Montana
Bureau of Mines and Geology Special Publication 62, 1:500,000.
Botz, M.K., 1969, Hydrogeology of the upper Silver Bow Creek drainage area,
Montana: MBMG Bulletin 75, 32 p.
Brietkrietz, Alex, 1964, Basin water data report, No. 1, Missoula Valley, Montana:
MBMG Bulletin 37, 43 p.
Burfeind, Walter J., 1967, A gravity investigation of the Tobacco Root Mountains,
Jefferson basin, Boulder batholith, and adjacent areas of southwestern Montana
(Ph.D. thesis): Bloomington, Indiana University, 90 p.
Burfeind, Walter J., 1970, Gravity investigations of selected batholiths and
basins of southwestern Montana: Trans. Am. Geophys. Union, v. 50, no. 10,
p. 535-537.
Cantwell, John, 1980, A gravity study of the Blackfoot-Nevada valley area, north-
western Montana (M.S. Thesis): Missoula, University of Montana, 39 p.
Chandler, V.W., 1973, A gravity and magnetic investigation of the McCarthy
Mountain area, Beaverhead and Madison Counties, Montana: M.A., Bloomington
Indiana University, 47 p.
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Claerbout, J.F., Fundamentals of Geophysical Data Processing, McGraw-Hill, Inc.,
United States, 1976.
Coffin, D.L., Brietkrietz, Alex, and McMurtrey, R.G., 1971, Surficial geology
and water resources of the Tobacco and upper Stillwater River valleys, north-
western Montana: Montana Bureau of Mines and Geology Bulletin 81, 48 p.
Coffin, D.L. ,and Wilke, K.R., Water resources of the upper Blackfoot River valley,
west-central Montana: Montana Dept. of Natural Resources and Conservation,
Water Resources Div., Technical Report Series, no. 1, 82 p.
Cole, G.A., Daniel, J.A., Heald, D. , Fuller, and Matson, R.E., 1981, Oil and Gas
Drilling and Coal Production Summary for Montana, 1981: MBMG Open-File
Report 59.
Cremer, E.A., III, 1966, Gravity determination of basement configuration, southern
Deer Lodge valley, Montana (M.S. thesis): Missoula, University of Montana,
23 p.
Crosby, G.W., 1968, Gravity investigation of the water-bearing strata in Swan
valley, Montana: Montana University Joint Water Resources Research Center,
unpublished report, 6 p. (Dept. Geology, Missoula, Univ. of MT).
Davis, W.E., Kinoshita, W.T., and Robinson, G.D., 1965, Bouguer gravity, aero-
magnetic, and generalized geologic map of the eastern part of the Three Forks
basin, Broadwater, Madison, and Gallatin Counties, Montana: U.S. Geological
Survey Geophysical Investigations map GP-498, 2 sheets, 1:62,500.
Davis, W.E., Kinoshita, W.T., and Robinson, G.D., 1965, Bouguer gravity, areo-
magnetic, and generalized geologic map of the western part of the Three Forks
basin, Jefferson, Broadwater, Madison and Gallatin Counties, Montana: U.S.
Geological Survey Geophysical Investigations map GP-497, 2 sheets, 1:62,500.
Davis. W.E., Kinoshita, W.T., Smedes, H.W., 1963, Bouguer gravity, aeromagnetic,
and generalized geologic map of East Helena and Canyon Ferry quadrangles and
part of the Diamond City quadrangle, Lewis and Clark, Broadwater, and Jefferson
Counties, Montana: U.S. Geological Survey Geophysical Investigations map
GP-444, 2 sheets, 1:62,500.
Dobrin, Milton B., Introduction to Geophysical Prospecting, 2nd ed., McGraw-Hill
Book Co., New York, 1960.
Donovan, J.J., and Sonderegger, J.L., 1981, Drilling report of Camp Aqua test
well no. 1 Hot Springs, Montana: Montana Bureau of Mines and Geology Open-
File Report 80, 74 p.
Donovan, J.J., Wideman, C.J., and Sonderegger, J.L., II, 1980, Geochemical
evaluation of shallow dilution of geothermal water in the Little Bitterroot
valley, Montana: Geothermal Resources Council, Transactions, v. 4, p. 157-161.
Geldon, Arthur L., and Curry, Robert R., 1979, Water resources of the Missoula
basin, western Montana and the effects of irrigation and withdrawals on the
water Budget, unpublished M.S. Thesis - University of Montana, 100 p.
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Freeman, V.L., Ruppel, E.T., and Klepper, M.R. , 1958, Geology of Part of the
Townsend Valley, Broadwater and Jefferson Counties, Montana: U.S. Geological
Survey Bulletin 1042-N, p. 481-556.
Gary, S.D., 1980, Quaternary geology and geophysics of the upper Madison valley,
Madison County, Montana (M.S. thesis): Missoula, University of Montana, 76 p.
Glancy, Patrick A., 1964, Cenozoic Geology of the Southeastern Part of the
Gallatin Valley, Montana (M.S. thesis), Bozeman, Montana State University,
1964, 67 p.
Grant, F.S., and West, G.F., 1965, Interpretation Theory in Applied Geophysics:
McGraw-Hill Book Co., New York.
Hackett, O.M., Visher, F.N., McMurtrey, R.G., and Steinhilber, W.L., 1960,
Geology and ground-water resources of the Gallatin Valley, Gallatin County,
Montana, with a section on surface-water resources by Frank Stermite and
F.C. Boner, and a section on chemical quality of the water by R.A. Krieger:
U.S. Geological Survey Water-Supply Paper 1482, 282 p.
Harrison, J.E., Griggs, A.B., and Wells, J.D., 1974, Preliminary geologic map of
part of the Wallace 1:250,000 sheet, Idaho-Montana: U.S. Geological Survey
Open-File Report 74-37, 1:250,000.
Hassemer, J.H., 1981, Principal facts and complete Bouguer gravity anomaly map
for the west half of the Butte 1x2 quadrangle, Montana: U.S. Geological
Survey Open-File Report 81-949, 39 p.
Hoffman, Dale Sheridan, 1941, Tertiary Vertebrate Paleontology and Paleoecology
of a portion of the Lower Beaverhead River Basin, Madison and Beaverhead
Counties, Montana, University of Montana, Ph.D., 1972, Paleontology.
Honkala, F.S., 1949, Geology of the Centennial region, Beaverhead County, Montana
(Ph.D. dissertation): University of Michigan, 145 p.
Horberg, L. , 1940, Geomorphic problems and glacial geology of the Yellowstone
valley, Park County, Montana: Journal of Geology, v. 48, p. 275-303.
Johns, W.M., 1970, Geology and mineral deposits of Lincoln and Flathead Counties,
Montana: Montana Bureau of Mines and Geology Bulletin 79, 182 p.
Johnson, P.P., 1981, Geology of the Red Rock fault and adjacent Red Rock valley,
Beaverhead County, Montana (M.S. thesis): Missoula, University of Montana,
88 p.
Kinoshita, W.T., Davis, W.E., Smedes, H.W. , and Nelson, W.H., 1964, Bouguer
gravity aeromagnetic, and generalized geologic map of Townsend and Duck
Creek Pass quadrangles, Broadwater County, Montana: U.S. Geological Survey
Geophysical Investigations map GP-439, 1:62,500.
Kinoshita, W.T. , Davis, W.E., and Robinson, G.D., 1965, Aeromagnetic, Bouguer
gravity, and generalized geologic map of Toston and Radersburg quadrangles
and part of the Devils Fence quadrangle, Gallatin, Broadwater, and Jefferson
Counties, Montana: U.S. Geological Survey Geophysical Investigations map
GP-496, 2 sheets, 1:62,500.
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Kleinkopf, M.D. , and Mudge, M.R. , 1972, Aeromagnetic, Bouguer gravity, and
generalized geologic studies of the Great Falls-Mission Range area, north-
western Montana: in Geophysical field investigations: U.S. Geological
Survey Professional Paper 726-A, p. A1-A19.
Knopf, Adolf, 1963, Geology of the northern part of the Boulder Batholith and
adjacent areas, Montana: U.S. Geological Survey Map I 361.
Konizeski, R.L., Brietkrietz, Alex, and McMurtrey, R.G., 1968, Geology and
ground-water resources of the Kalispell valley, northwestern Montana:
Montana Bureau of Mines and Geology Bulletin 68, 42 p.
Konizeski, R.L., McMurtrey, R.G., and Brietkrietz, Alex, 1968, Geology and
ground-water resources of the Deer Lodge valley, Montana, with a section on
Gravimetric survey, by E.A. Cremer, III: U.S. Geological Survey Water-Supply
Paper 1862, 55 p.
Kuenzi, W. Davis, and Fields, Robert W., Tertiary Stratigraphy, Structure, and
Geologic History, Jefferson Basin, Montana: Geological Society of America
Bulletin, v. 82, p. 3373-3394, December 1971.
Lankston, Robert Wayne, 1975, A geophysical investigation in the Bitterroot
valley, western Montana (Ph.D. dissertation): Missoula, University of
Montana, 112 p.
LaPoint, D.J., 1971, Geology and geophysics of the southwestern Flathead Lake
region, Montana (M.S. thesis): Missoula, University of Montana, 110 p.
Leonard, R.B., and Wood, W.A., 1980, Geothermal gradients in the Missoula and
Bitterroot Valleys, west-central Montana: U.S. Geological Survey Water-
Resources Investigations 80-89, 15 p.
Lorenz, H.W., and McMurtrey, R.G., 1956, Geology and occurrence of ground water
in the Townsend valley, Montana: U.S. Geological Survey Water-Supply Paper
1360-C, p. 171-290.
Lorenz, Howard W., and Swenson, Frank A., 1951, Geology and ground-water resources
of the Helena Valley, Montana: U.S. Geological Survey Circular 83, 68 p.
Manghnani, M.H., and Hower, John, 1962, Structural significance of a gravity
profile in the Bitterroot valley, Ravalli County, Montana: Geological Society
of America Special Paper 68, p. 93.
McMannis, William J., 1955, Geology of the Bridger Range, Montana: Bulletin of
the Geological Society of America, vol. 66, pp. 1385-1430.
McMannis, W.J., 1968, Resume of Depositional and Structural History of Western
Montana: AAPG Bull. November, v. 49, no. 11, pp. 1801-1823.
McMurtrey, R.G., and Konizeski, R.L., 1956, Progress report on the geology and
ground-water resources of the eastern part of the Bitterroot Valley, Montana:
Montana Bureau of Mines and Geology Information Circular No. 16, 28 p.
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McMurtrey, R.G., Konizeski, R.L., and Brietkrietz, Alex, 1965, Geology and ground-
water resources of the Missoula basin, Montana: Montana Bureau of Mines and
Geology Bulletin 47, 35 p.
McMurtrey, R.G., Konizeski, R.L., and Stemitz, F. , 1959, Geology and water
resources of the Bitterroot Valley, Montana: Montana Bureau of Mines and
Geology Bulletin 9, 45 p.
Meinzer, O.E. , 1917, Artesian water for irrigation in the Little Bitterroot
valley, Montana: U.S. Geological Survey Water-Supply Paper 400-B, p. 9-37.
Mertle, John B., Jr., Fisher, R.P., and Hobbs, S.W., 1951, Geology of the Canyon
Ferry quadrangle, Montana: U.S. Geological Survey Bulletin 972, 97 p.
Mifflin, Martin D., 1963, Geology of a Part of the Southern Margin of the Gallatin
Valley, Southwest Montana: M.S. Thesis 1963, Montana State University,
Bozeman, 111 p.
Miller, M.R., 1970, City of Townsend Water Problem: Montana Bureau of Mines and
Geology Open-File Report, 20 p.
Montana Department of Natural Resources and Conservation, Water Resources Division,
October 1976, The Framework Report, Vol. one, 101 p.
Montana Department of Natural Resources and Conservation, Oil and Gas Division:
Annual Review for the year 1980, Oil and Gas Volume 24, 44 p.
Moreland, Joe A., Leonard, Robert B., Reed, T.E., Clausen, Richard 0., and
Wood, Wayne A., 1979, Hydrologic data from selected wells in the Helena Valley,
Lewis and Clark County, Montana: U.S. Geological Survey Open-File Report
79-1676, 54 p.
Moreland, Joe A., and Leonard, Robert B., 1980, Evaluation of shallow aquifers
in the Helena Valley, Lewis and Clark County, Montana: U.S. Geological Survey
Water Resources Investigations Open-File Report 80-1102, 24 p.
Mudge, M.R., Erickson, R.L., and Kleinkopf, Dean, 1968, Reconnaissance geology,
geophysics and geochemistry of the southeastern part of the Lewis and Clark
Range, Montana with Spectrographic data by G.C. Curtin and A.P. Mananzino,
and a section on Isotopic composition of lead by R.E. Zartman: U.S. Geological
Survey Bulletin 1252-E, p. E1-E35.
Myers, W.B., and Hamilton, W., 1964, Deformation accompanying the Hebgen Lake
earthquake of August 17, 1959, in The Hebgen Lake, Montana Earthquake of
August 17, 1959: U.S. Geological Survey Professional Paper 435, p. 55-98.
Nettleton, L.L., Geophysical Prospecting for Oil, McGraw-Hill, New York, 1940,
pp. 101-102.
Nettleton, L.L., Gravity and Magnetics in Oil Prospecting, McGraw-Hill, Inc,
United States, 1976.
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Norbeck, P.M. , 1980, Preliminary evaluation of deep aquifers in the Bitterroot
and Missoula Valleys in western Montana: Montana Bureau of Mines and
Geology Open-File Report 46, 15 p.
Parasnis, D.S., (1962), Principles of Applied Geophysics, London, Methuen, p. 40.
Pardee, J.T. , 1925, Geology and ground-water resources of the Townsend Valley,
Montana: U.S. Geological Survey Water-Supply Paper 539, 61 p.
Pardee, J.T. , 1950, Late Cenozoic block faulting in western Montana: Geological
Society of America Bulletin, v. 61, p. 359-406.
Parker, John S., 1961, A preliminary seismic investigation of Tertiary basin fill
in the Jefferson Island Quadrangle, Montana: (unpublished M.A. thesis),
Indiana University, Bloomington, Indiana, 35 p.
Petkewich, Richard M., 1972, Tertiary Geology and Paleontology of the Beaverhead
East Area, southwest Montana: Missoula, University of Montana, Ph.D. 1972,
365 p.
Renick, Howard, Jr., 1965, A gravity survey of the Boulder batholith and the
Prickley Pear Valley near Helena, Montana: "The Compass", 42(4), p. 217-224.
Reynolds, M.W., 1979, Character and extent of basin-range faulting, western
Montana and east-central Idaho, in Newman, G.W. and Goode, H.D. (eds.), 1979
Basin and Range Symposium and Great Basin Field Conference: Rocky Mountain
Association of Geologists - Utah Geological Association, p. 185-193.
Richard, Benjamin Hinchcliff, 1966, Geologic History of the Intermontane Basins
of the Jefferson Island Quadrangle, Montana: Indiana University, Ph.D. 1966
Geology, Bloomington, Indiana, 121 p.
Robinson, G.D., 1961, Origin and Development of the Three Forks Basin, Montana:
Geological Society of America Bulletin, v. 72, p. 1003-1014.
Robinson, G.D., 1963, Geology of the Three Forks quadrangle, Montana, with
sections on Petrography of igneous rocks by H.F. Barnett: U.S. Geological
Survey Professional Paper 370, 143 p.
Robinson, G.D., 1967, Geologic Map of the Toston Quadrangle, southwestern
Montana: U.S. Geological Survey Map 1-486.
Ross, C.P., 1952, The eastern front of the Bitterroot Range, Montana: U.S.
Geological Survey Bulletin 947-E, pp. 135-175.
Schofield, J.D., 1980, A gravity and magnetic investigation of the eastern
portion of the Centennial valley, Beaverhead County, Montana (M.S. thesis):
Butte, Montaan College of Mineral Science and Technology, 94 p.
Skeels, D.C., Ambiguity in Gravity Interpretation, Geophysics, Vol. 12, pp. 43-56,
1947.
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Smith, Robert Baer, 1967, A Regional Gravity Survey of Western and Central
Montana, (Ph.D. Thesis): University of Utah, Salt Lake City, 193 p.
Sonderegger, J.L., Berg, R.B., and Mannick, M.L., 1980, Geologic map of the
northern portion of the Upper and Lower Red Rock Lake quadrangles, Beaver-
head County, Montana: Montana Bureau of Mines and Geology Open-File Report
47, 1:62,500.
Sonderegger, J.L., Wideman, C., Donovan, J.J., Halvorson, J., Kovacich, S., and
Wyatt, G., 1980, Geothermal studies in Montana with a summary report on
geophysical investigations at Warm Springs State Hospital: Montana Bureau
of Mines and Geology Open-File Report 37, 15 p.
Stickney, Michael C., 1980, Seismicity and gravity studies of faulting in the
Kalispell valley, northwest Montana (M.S. Thesis): Missoula, University of
Montana, 82 p.
Talwani, M., Worrel, J.L., and Landismah, M., Rapid Computations for Two-Dimensional
Bodies with Application to the Mendocino Submarine Fracture Zone: Journal of
Geophysical Research, vol. 64, pp. 49-59, 1959.
Telford, W.M., Geldart, L.P., Sheriff , R.E., and Keys, D.A., Applied Geophysics,
Cambridge University Press, Cambridge, 1976, p. 61.
United States Bureau of Mines: 1976-present, Keystone Coal Industry Manual.
United States Department of Commerce, Bureau of Census, PH680-V-28, Montana, 1980.
United States Department of the Interior, Minerals in the Economy of Montana, 1979.
Vane, Gregg, 1972, A Seismic Reflection Investigation of the Jefferson River Basin,
Jefferson, Madison, and Silver Bow Counties, Montana, (M.S. Thesis): Indiana
University, Bloomington, Indiana, 38 p.
Wantland, D., 1953, Second phase of geophysical investigations in connection with
U.S. Geological Survey ground-water studies in the Gallatin River valley,
Montana: U.S. Bureau of Reclamation, Engineering Geology Branch, Geology
Report no. G-121, 29 p.
Wehrenberg, J.P., 1968, Structural development of the northern Bitterroot Range,
western Montana: G.S.A. Special Papers 115, p. 456.
Wilke, K.R., and Coffin, D.L. , 1973, Appraisal of the quality of ground water in
the Helena Valley, Montana: U.S. Geological Survey Water Resources Investiga-
tions 32-73, 31 p.
Wilke, K.R., and Johnson, M.V., 1978, Maps showing depth to water table, September
1976, and area inundated by the June 1975 flood, Helena Valley, Lewis and
Clark County, Montana: U.S. Geological Survey Open-File Map 78-110.
Wilson, Daniel A. , 1962', A seismic and gravity investigation of the North Boulder
River and Jefferson River Valleys, Madison and Jefferson Counties, Montana
(unpublished M.A. thesis): Indiana University, Bloomington, Indiana, 43 p.
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Witkind, I.J. , 1975, Preliminary map showing known and suspected active faults
in western Montana: U.S. Geological Survey Open-File Report 75-285,
1:500,000.
Wopat, M.A., Curry, W.E., Robins, J.W., and Marjaniemi, D.K., 1977, Favorability
for uranium in Tertiary sedimentary rocks, southwestern Montana (DOE Contract
EY-76-C-13-1664): Bendix Field Engineering Corporation, Grand Junction,
Colorado, Report GJBX-56(77), 152 p.
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APPENDIX A
WELL-NUMBERING SYSTEM
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WELL NUMBERING SYSTEM
In this report, locations are numbered according
to geographic position within the rectangular grid
system used by the U.S. Bureau of Land Management.
The location number consists of as many as 12
characters. The first three characters specify the
township and its position south of the Montana base
line. The next three characters specify the range and
its position east of the Montana principal meridian.
The next two characters are the section number. The
next three characters designate the quarter section
(160-acre tract), quarter-quarter section (40-acre
tract), and quarter-quarter-quarter section (10-acre
tract), respectively, in which the well is located.
The subdivisions of the section are designated A, B, C
and D in a counterclockwise direction, beginning in the
northeast quadrant. When more than one well is des-
cribed within a 10-acre tract, consecutive digits are
added to the well number. For example, as shown on
Figure 11-14, well 05S54E16ACC is the first well inven-
toried in the SWV SW*s NE^ sec. 16, T. 5 S., R. 54 E.
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Diagram showing well-numbering system.
Figure 11-28
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APPENDIX B
GLOSSARY OF TERMS
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Acre-foot - A unit for measuring the volume of water. It is equal to the
quantity of water required to cover 1 acre to a depth of 1 foot, and
is equal to 43,560 cubic feet or 325,851 gallons.
Alluvium - A general term for clay, silt, sand and gravel deposited by
running water as sorted to semisorted sediment.
Aquifer - A formation, group of formations or part of a formation that
contains sufficient saturated permeable material to yield significant
quantities of water to wells or springs.
Arid - A climate characterized by dryness, variously defined as rainfall
insufficient for plant life or for crops without irrigation; less
than 10 inches of annual rainfall.
Artesian - Artesian is snyonymous with confined. Artesian water and
artesian water body are equivalent, respectively, to confined ground
water and confined water body. An artesian well is a well deriving
its water from an artesian or confined water body. The water level
in an artesian well stands above the top of the artesian water body
it taps. If the water level in an artesian well stands above the
land surface, the well is a flowing artesian well; however, an
artesian well does not have to flow. If the water level in the well
stands above the water table, it indicates that the artesian water
can and probably does discharge to the unconfined water body.
Clastic sediments - Sediments formed from preexisting rocks and transported
to their location of deposition.
Colluvium - A general term applied to a loose heterogeneous mixture of
gravels, sands, silts and clays deposited at the base of a slope.
Dissolved-solids concentration - The total dissolved minerals in water,
expressed as the weight of mineral per unit volume of water, without
regard to the type of minerals.
Disturbed Belt - A zone roughly 25 miles wide along the eastern mountain
front which was tectonically disturbed during the formation of the
Rocky Mountains, but mountains did not develop in this zone.
Drawdown - A lowering of the water table or potentiometric surface caused
by puming ground water from wells.
Drift - Both stratified and unstratified material deposited by a glacier
or its associated fluvial waters.
Effluent stream - A stream which receives water from the zone of saturation;
a gaining stream.
Evapotranspiration - The combination of water lost through evaporation and
transpiration.
Fluvial - Pertaining to a river.
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Geosyncline - An elongate, mobile downwarping of the earth's crust, usually
many hundreds of miles long and tens to several hundred miles wide, in
which many thousands of feet of sediment may accumulate.
Histogram - A vertical bar-graph representation of a frequency distribution
in which the height of bars is proportional to frequency of occurrence
within each class interval.
Hydraulic conductivity - A coefficient of proportionality describing the
rate of which water can move through a permeable medium.
Igneous extrusions - Molten magma which has been extruded onto the surface
of the earth and cooled to a rock.
Igneous intrustions - Molten magma which has been emplaced into pre-existing
rocks and cooled to a rock.
Infiltration - The flow of water from the land surface into the soil layers.
Influent stream - A stream which contributes water to the zone of saturation;
a losing stream.
Injection well - A well into which water or other fluids are pumped for
varying purposes such as disposal, secondary oil recovery or
increased yield.
Isocontours - A line connecting points of equal concentrations of a solute
in ground water.
Isopoch - A line drawn on a map through points of equal thickness of a
designated stratigraphic unit.
Lacustrine - Pertaining to or formed in a lake.
Laramide Orogeny - A time of deformation during which the Rocky Mountains
were developed, extending from late Cretaceous until the end of the
Paleocene.
Lithology - The description of rocks in hand specimen and in outcrop on
the basis of such characteristics as color, structure and mineralogic
composition.
Loess - A widespread, homogeneous, commonly nonstratified deposit of wind-
blown dust that is generally believed to be Pleistocene age.
Mean annual runoff - The average yearly flow from rainfall or melted snow
which ultimately reaches a surface stream.
Metasediments - A sedimentary rock which has been subjected to metamorphism.
Microthermal - Pertaining to a climate characterized by low temperature.
Moraine - A mount, ridge or other distinct accumulation of unsorted,
unstratified glacial drift, predominantly till, deposited by the
action of glacier ice in a variety of topographic land forms.
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Outwash deposits - Stratified sediments deposited from meltwater streams
of glaciers.
Overthrust Belt - Syonnymous with Disturbed Belt.
Perched aquifer - An unconfined aquifer overlying the main water saturated
zone.
Potentiometric surface - A surface which represents the static head. As
related to an aquifer, it is defined by the levels to which water
will rise in tightly cased wells. Where the head varies appreciably
with depth in the aquifer, a potentiometric surface is meaningful only
if it describes the static head along a particular specified surface
or stratum in that aquifer. More than one potentiometric surface is
then required to describe the distribution of head. The water table
is a particular potentiometric surface.
Rainshadow effect - Usually a very dry region on the lee side of a mountain
where rainfall is substantially less than on the windward side.
Recharge - Ground-water replenishment to an aquifer.
Saline - A general term for naturally occurring soluble salts, such as
sodium chloride, sodium carbonate, sodium nitrate, potassium salts, etc.
Sedimentary - Formed by deposition or accretion of grains or fragments of
rock-making materials. Applied to all kinds of deposits from the
waters of streams, lakes or seas and in a more general sense to deposits
of wind and ice.
Snow Forest climate - A climate where the coldest month has an average
temperature below 0 C and the warmest month has an average temperature
above 10 C.
Static water level - The water level of a well that is not being effected
by withdrawal of ground water.
Steppe - An extensive, treeless grassland area generally considered drier
than the prairie.
Storativity - The volume of water an aquifer releases from or takes into
storage per unit surface area of the aquifer per unit change in head;
storage coefficient.
Subhumid - A climate type that is transitional between humid and subarid
types according to quantity and distribution of precipitation.
Tectonic activity - Pertaining to the forces involved which create
structures.
Till - Unsorted and unstratified drift deposited by a glacier.
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Transmissivity - The rate at which water is transmitted through a unit
width of an aquifer under a unit hydraulic gradient.
Tundra climate - A type of polar climate having a mean temperature in the
warmest month of between 0 and 10 C.
Unconsolidated deposits - Primarily clays, silts, sands and gravels that
are loosely arranged and not cemented together.
Water-table aquifer - An unconfined aquifer where the pore water pressure
is atmospheric.
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APPENDIX C
MONTANA WATER LAW
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The appropriative doctrine of water rights, "first in time, first in
right," applies exclusively in Montana. Prior to 1973, a water right was
acquired by simply making a diversion and posting notice of such diversion.
A filing was to be made in the county office, but the courts had ruled that
even this was not required. The appropriator did have to put the water to
beneficial use. The appropriation of ground water to beneficial use prior
to January 1, 1962 was recognized as a water right for the first time by the
1962 Montana Groundwater Law, but surface rights with a priority preceding
that date were given priority over all prior or subsequent ground-water rights.
The 1973 Montana Water Use Act established a uniform central system for the
acquisition, administration and determination of all water rights. It also
mandated, the adjudication of all existing rights. The appropriator is required
to file for a permit with the Department of Natural Resources and Conservation
(DNRC), to obtain a new water right if it involved construction of a new
surface water diversion or impoundment, or a water well with an anticipated
beneficial use of more than 100 gpm. The DNRC was directed to issue permits if
applicants complied with certain conditions including the requirements that:
(1) Unappropriated waters exist which the applicant can put to beneficial
use in the amount and at the time proposed in the application.
(2) The rights of prior appropriators will not be adversely affected.
(3) The proposed means of diversion or construction is adequate.
Beneficial use is defined as "a use of water for the benefit of the appropriator,
other persons, or the public, including but not limited to, agricultural
(including stock water), domestic, fish and wildlife, industrial, irrigation,
mining, municipal power, and recreational uses..."
who will appoint Water Masters to review the permit applications and that each
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water judge shall study and adjudicate all water rights granted thereby. Such
judges have now been appointed and they estimate that the water rights, both
surface and ground, for which applications are filed prior to April 30, 1982,
will be adjudicated within 10 years. When this occurs, the State and its water
users will, for the first time, have a written record of all water rights, in
Montana, quantified in time and amounts of water. For a compilation on the
rules and regulations pertaining to Montana's ground water, reference should
be made to the Montana Code Annotated, Volume 13, Sections 85-2-501 through
85-2-520.
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