Montana Ground-Water Assessment Atlas No. 2, Part B, Map 4 December 2004

Montana Bureau of Mines and Geology A Department of Montana Tech of The University of Montana

Potentiometric Surface Map of the Southern Part of the Flathead Lake Area, Lake, Missoula, Sanders Counties, Montana by John I. LaFave

Note - this map was originally published at a scale of 1:100,000 but the page sizes have been modified to fit the size of the paper in your printer. A full sized 36” X 48” colored print of this map can be ordered from the Office of Publications and Sales of the Montana Bureau of Mines and Geology, 1300 West Park Street, Butte, MT 59701. Phone: 406-496-4167 Web Address: www.mbmg.mtech.edu Montana Bureau of Mines and Geology A Department of Montana Tech of The University of Montana

R 24W R 23WLake County R 22W R 21W

. s e R rt 30’ 114 a b b u H Lake 3699 Mary Ronan 3527 3500 Dayton Valley T 25N (3701 ft.) 3430

3400 3300

3200 3224

3096 3563 3168 3048 3100 Reservation Boundary D 3212 a y 3053 to n Flathead County C r. 2984 Sanders County 2986 3000

3100 2900 2891 2881 2898 2887 2900 3000

2874 2850 T 24N 2850

2900 2811 3221 2910 2905 2780

2800 2893 2888 2906 2873 2976

2798 Flathead County 3009 2774 Lake County

2766 3266

00

8 Montana Ground Water Assessment Atlas No. 2, Part B, Map 4 December 2004

R 20W R 19W R 18W R 17W

F la th S e L a w a d k C e o a C u

114 00’ 114 n o n u t n y L ty a ( 3 k 0 3064 6 e 7 3100 f 3102 Swan t .) 3072 T 25N

3150 3100

3085

Reservation Boundary

3110

Range

3200

3249

T 24N 3200 Reservation Boundary

2863 Flathead Lake Swan Valley 2882 (2892 ft.) 2885

S

w

2919 a

n

00

29 2892 8

2 3901 2774

3470

3371 47 45’ 3 T 23N 3484 3102 3210 3 Little Bitterroot 3069 3056 Valley 3008 3 3019

2769 L 3096 i 2765 t t l 3158 3070 2777 e B 2758 i t t S 2766 e r r 3050 o a 2766 2776 o 2912 t 3352 3042 l 3000 R i iv s 2800 e 2950 C r h 2891 2900 2900 a 2772 2765 2850 b 2819 2761 2771 i 2767 2909 n 2771 2800 2871 T 22N e 2771 2941 2846 2776 2913 2766 t 2750 2762 2853 2941 2782 2770 2772 2763 2772 2716 2790 2927 2764 2771 2829 2 2761 2946 2684 2853 2935 2750 2850 2757 2 2841 2750 M 2741 30

2861 2750

o 2700 2800 2955

Hot Springs 2928 2850

2650 s u 2900 l

2735 l 2950 i 2825 Lake County n H Sanders County M t w 2742 a e 2758 i o i V 2755 n

u y s 2886 e ll n a T 21N 2914 3591 V t L a i tt 2984 le i B i n tt e 2916 r r s o er o iv t R R 2844 iv e Camas Prairie r

Basin 2847

2876 2700

d 2828 a 2813 e Lowe h R 47 30’ t 2892 29 2893 2911 3021 2889 R i 2875 v 3046 2896 e 2901 r

2904 3300 3300 2891 2823 3262 3000 47 45’ 3110 2922

2883 2900 2881 T 23N 2867 3265 3083 2890 9 2898 3040 2907 2876 3288 2883 3049 3007 2904 3367

3057 2901 3307

2806 2898 2900 2883

2906 2915 3357 3400 2915 2960 2952 2923 2941 Polson 2949 3400 3399 2968 2972 2944 2972 2989 2950 2960 2959 Moraine 2961 3000 2961 3050 Polson 3219 3222 3007 3100 2903 2973 3391 T 22N Mission 3150 3226 3241 3421 2942 3245 3439 2981 3319 3086 3195 3311 3234 3118 3230 3442 3118 3200 3286 3289 3438 2995 3201 3485 2954 3440 Pablo Res. 3083 3507 (3210 ft.) 3222 3073 3469

2986 3186 14 3110 R 18W R 17W Mission Valley 3043 3223 3111 3176 3009 3115 3040 3222

3014 3047 3116 Pablo 3077 3063 3033 3393 3058 k 3055 3052 e 3085 3050 re 3029 C 3062 3044 EXPLANATION 3048 3080 3034 3134 3083 3077 3031 2800 Potentiometric surface contour showing line 3093 3054 T 21N of equal water-level altitude, dashed where 3006 3105 3062 approximate. 3062 3339 3036 3029 Contour interval is 50 feet in the Mission and 3000 3003 Little Bitterroot Valleys, and 100 feet in the Dayton, d u Swan and Jocko Valleys. M 3060 3069 3247 3048 3048 Generalized direction of ground-water flow 3011 3055 3201 3022 3008 3238 3200 2968 Well completed in the alluvium 3020 3067 3100 2999 3073 with water-level altitude. 3050 3040 Well completed in the alluvium less than 75 feet deep, 2971 3301 3294 2968 3026 Ronan Mission Valley only. 3356 3147 Ra 3037 2927 Well completed in the bedrock (Belt Supergroup) 3023 3000 Township boundary 3010 n er Crow Res C 47 30’ Section boundary 47 30 h R 2786 t a l 2900 2794 F 2631 2850 28 2800 T 20N 2794 2795 2650 289 C 2644 a m 2863 2796 a s 2645 2950 2796 2543

C 2794 ls re l e i k 2539 H

2946 e s e i o

M

2718 2715 2711 T 19N 2522

2654 267 2528 2 2524 2622 2600 Mis sion 2539

Fla the ad T 18N 2529 2538 r Rive 2507 2548 2507 R 23W 30’ 114 2550 R 24W R 22W J oc ko

Potentiometric Surface Map surface topography and ground-water flow is feet. The distribution of well depths is variable; over a distance of about 20 miles along the axis fill deposits consist of Tertiary (?) alluvial deposits away from the mountains along the valley margins between Mission and Post Creeks west of of the valley. The relatively flat gradient reflects overlying the bedrock, and Quaternary alluvium R of the Southern Part of the toward the streams that drain the valleys. The Highway 93 and in the alluvium associated with the low relief of the surface topography in the and lacustrine deposits; there is no evidence of ive ground-water flow systems in the valleys are Mud Creek near Pablo, well depths are generally Little Bitterroot Valley as well as the high glacial till in the valley (Kendy and Tresch, 1996). r Flathead Lake Area, Lake, strongly controlled by topography and the less than 75 feet. Where well depths are less than transmissivity of the Lone Pine aquifer. The deepest well in the valley penetrated 725 Sanders, and Missoula distribution of permeable layers within the valley- 75 feet, ground water occurs under unconfined feet of valley-fill material without encountering fill deposits. Summaries for the individual valleys conditions. In the center of the valley west of Records from GWIC indicate that there are at bedrock. Counties, Montana for which the potentiometric surface was mapped Highway 93 well depths are typically greater least 482 wells completed in the Little Bitterroot are presented below. than 250 feet; east of Highway 93 toward the Valley; 262 of them are completed in the Lone Records from GWIC indicate that there are at R 21W by Mission Mountain front, well depths are typically Pine aquifer. Yields from wells in the Lone Pine least 72 wells completed in the valley that supply John I. LaFave On this map ground-water flow appears to be less than 250 feet. The median well depth for the aquifer are relatively high compared to other domestic and stock water. Most wells are horizontal, but there also are important vertical valley is 154 ft (figure 1). valleys and are reportedly as much as 1,100 gpm, completed in the valley-fill deposits; some are components. Vertical ground-water flow is with a median of 60 gpm (figure 2). Most wells in the surficial alluvium (less than 50 feet deep) Author's Note: This map is part of the Montana indicated by differing water-level altitudes in Across the rest of the valley, most water-bearing completed in the Lone Pine aquifer are between but most are in alluvium that is buried by Bureau of Mines and Geology (MBMG) Ground- closely spaced wells that are completed at units are buried by layers of silt and/or clay and 200 and 330 feet deep (figure 1). There are lacustrine silts and clays. Around the valley Water Assessment Atlas for the Flathead Lake different depths. Vertical flow may be upward ground water is under semi-confined to fully records of 76 wells completed in the Belt bedrock; margin there are 17 wells completed in Belt Area ground-water characterization. It is intended or downward depending on position in the flow confined conditions. In a wedge-shaped area most of the bedrock wells are located in and near bedrock. Most wells are less than 200 feet deep, to stand alone and describe a single hydrogeologic system, and the geologic framework. Recharge between Ronan and Pablo west of Highway 93, the town of Hot Springs and along the valley and the median well depth is 80 feet (figure 1). REFERENCES aspect of the study area, although many of the areas, discharge areas, and places where low well depths are 300 to 500 feet below land surface, margin. Bedrock well depths and yields are more Reported yields are generally less than 30 gpm; Abdo, G., 1997, Reappraisal of hydrogeology of area's hydrogeologic features are interrelated. permeability layers separate more permeable but the potentiometric surface is within about 20 variable. Most of the bedrock wells are between the median reported yield is 10 gpm (figure 2). the Little Bitterroot Valley, northwestern For an integrated view of the hydrogeology of units are settings where vertical flow can occur. feet of land surface and there are some flowing 50 and 570 feet deep and well yields range from Ground water flows away from the valley margins Montana: Montana Bureau of Mines and the Flathead Lake Area the reader is referred to Typically, in recharge areas (such as along the wells. less than 1 up to 500 gpm with a median of 25 toward Camas Creek in the middle of the valley. Geology Open File Report 350, 43 p. Part A (descriptive overview) and other Part B mountain fronts) shallow wells have higher water gpm. maps of the Montana Ground-Water Assessment levels; this indicates a downward gradient and Well yields were reported for about 1,600 wells USE OF THIS MAP Boettcher, A.J., 1982, Ground-water resources Atl N 2 downward flow Upward flow occurs in the in the Mission valley and range from less than Swan valley This potentiometric surface map is useful for in the central part of the Flathead Indian n

Res. C ro ge 47 30’ Section boundary w 3150 Major road 867 2889 2976 k 2961 ee 2948 Cr Secondary road 2964 3017 T 20N 2978 2950 3017 Flathead Indian Reservation boundary 91 2871 2981 2900 County boundary

2831 2867 93 Hwy. Stream 2914 3005 2946 3095 2864 3006 2912 Kicking Horse2938 Res. Federal/Tribal/State lands (3062 ft.) 2925 Other lands 2850 Ninepipe Res.

2919 (3 0 3082 2918 1 0 2919 ft .) 3013 3174 2843 2872 2897 2 0 2 4 6 Miles

M cD ona 2800 2800 ld L 2842 ake (3 2841 596 Scale 1:100,000 ft.) 2750 UTM Projection Zone 11 NAD27 2820 2748 2700 2743 2859 2779 2857 2893 2820 T 19N Flathead Lake Area

2783 2720 2748 71 3067 Map Area k 2650 2677 e 2716 re C

t Cr os 2721 2774 eek P 2716 2721 3064 3064

3070

3057

2748 2897 2780 2744 2907 2747 M is si on 2938 es. n R sio Mis 2909 St. Ignatius 3104 T 18N 2969 3068 3182 2893 3149 2951 3168 3388 3252 Ground-Water Characterization Program Study Areas 2979 3073 C 3151 re ek 2692 2692 3560 3428 Explanation 2694 3450 n = number of samples Percentiles 95th

75th 700 700

47 15’ 50th 600 600 2800 25th 2900 3000 2900 2887 500 500 2795 5th 2803 feet) T 17N ( 400 Atlas No. 2. downward flow. Upward flow occurs in the in the Mission valley and range from less than Swan valley This potentiometric surface map is useful for in the central part of the Flathead Indian discharge areas which generally coincide with 1.0 gallon per minute (gpm) up to 2,400 gpm, The Swan valley is a relatively narrow north- estimating the general direction of ground-water Reservation, northwestern Montana: Montana INTRODUCTION the valley bottoms. In these areas water-level the median yield is 20 gpm (figure 2). Most of trending intermontane basin that is bounded by flow, identifying areas where flowing artesian Bureau of Mines and Geology Memoir 48, This map presents the potentiometric surface of altitudes increase with depth, indicating an the high capacity wells (yields > 200 gpm) occur the Mission Range on the west and the Swan wells might occur, and estimating the water-level 28 p. the major valley-fill aquifers in the southern part upward component of ground-water flow. in the center of the valley north of Post Creek, Range on the east. The north-flowing Swan River altitude in a non-flowing well. Ground water of the Flathead Lake Ground Water south of the Pablo Reservoir and west of Highway and its tributaries drain the valley and empty into flows from high altitude to low altitude. If the Briar, D.W., Lawlor, S.M., Stone, M. A. J., Characterization Study Area. The area is Mission valley 93. Swan Lake. The mapped area includes only that approximate land-surface altitude at a location Parliman, D. J., Schaefer, J. L., and Eloise characterized by a series of north-northwest The Mission valley occupies part of a north- part of the valley between the Missoula County is known (for example, determined from a Kendy, 1996, Ground- water levels in trending, structurally controlled intermontane trending, intermontane basin that is bounded by Jocko valley line and Swan Lake. Normal faults have down- topographic map), the corresponding point on Intermontane basins of the northern Rocky basins that are bounded by mountains formed the Salish Mountains to the west, the Mission The Jocko valley occupies a northwest trending dropped the valley floor relative to the mountains the potentiometric surface map can be found and Mountains, Montana and Idaho: U.S. mostly of metamorphosed sedimentary rocks of Range to the east and the Jocko Hills to the south; intermontane basin in the southernmost part of and the valley-fill sediments are as much as 5,000 the altitude of the potentiometric surface Geological Survey Hydrologic Atlas HA-738- the Proterozoic Belt Supergroup (bedrock). The Flathead Lake marks the northern boundary. The the study area. The northwest flowing Jocko feet thick (Kendy and Tresch, 1996). Most of the estimated. Subtracting the potentiometric surface B, scale 1:750,000. valleys are filled with consolidated to Flathead River drains the Mission Valley and River and its tributaries drain the valley, and the valley floor is covered with glacial till; glacial altitude from the land surface altitude yields the unconsolidated, Tertiary and Quaternary marks most of its western boundary. Drainage surface drainage has been modified by more than outwash and alluvium are present near some of approximate level at which water will stand in Donovan, J. J., 1985, Hydrogeology and sediment; most of the surficial valley-fill deposits within the valley has been modified by an 60 miles of irrigation canals (Thompson, 1988). the tributaries to the Swan River. Ground water a well. It may also show that the altitude of the geothermal resources of the Little Bitterroot are of glacial or glaciolacustrine origin. The extensive network of irrigation canals and Ground water in the valley-fill and the bedrock from the glacial sediments supplies most of the potentiometric surface is above land surface at Valley, northwestern Montana: Montana Flathead River and its tributaries drain the valleys reservoirs (Boettcher, 1982; Kendy and Tresch, around the valley margin supplies all the drinking residents in the valley. a given location and a flowing well could be Bureau of Mines and Geology Memoir 58, in the mapped area. Ground water in the valley- 1996). The valley floor generally slopes to the water within the Jocko valley (Kendy and Tresch, expected. 60 p. fill sediment and the fractured bedrock along the south-southwest away from the Polson moraine 1996). Records from GWIC indicate at least 100 wells valley margins is an important source of (maximum altitude 3,487 ft) on the north end of are completed in the mapped part of the valley. MAP CONSTRUCTION Kendy, Eloise and Tresh, Ruth E., 1996, municipal, domestic, irrigation and stock water. the valley, toward the Flathead River and to Records from GWIC indicate that there are at Most of the wells are between about 50 and 120 This map was constructed by hand-contouring Geographic, geologic, and hydrologic where the Flathead River exits the valley (altitude least 570 wells completed in the valley; the feet deep (figure 1) and completed in permeable water-level altitudes measured in wells between summaries of intermontane basins of the Overviews of the area's geology are presented 2,600 ft). The Valley View Hills and The Moiese median well depth is 100 feet (figure 1), and layers of sand and gravel buried in till. Ground May 1996 and November 1996. In the Little northern Rocky Mountains, Montana: U.S. in Smith (2002a, 2002b), and Tuck and others Hills, which are cored by Belt bedrock, protrude wells are generally shallower (less than 75 feet) water flows from the valley margins toward the Bitterroot Valley, data were supplemented by Geological Survey Water Resources (1996). The hydrogeology of various parts of the from the western part of the valley floor. in the northern part of the valley, north of Arlee. center of the valley and appears to be under measurements from Abdo (1997) made in 1993- Investigations Report 96-4025, 233 p. study area are presented in Kendy and Tresch Most of the wells are completed in alluvial unconfined to semi-confined conditions; flowing 1994. Map accuracy is affected by data (1996), Briar and others (1996), Slagle (1988), The Polson moraine marks the southern extent deposits associated with the Jocko River and its wells are present in the valley bottoms. The distribution, field measurement errors, accuracy Levish, D.R., 1997, Late Pleistocene Makepeace (1994), Donovan (1985), Boettcher of valley-filling ice during the last glacial tributaries and in the Belt bedrock surrounding highest reported well yield in the valley is 100 of well locations, and errors in interpretation. sedimentation in Glacial Lake Missoula and (1982), Thompson (1988) and Abdo (1997). maximum (Levish, 1997). South of the moraine the valley, however a few wells along the northern gpm; most yields are less than 30 gpm with a Points at which water levels have been measured revisited glacial history of the Flathead Lobe the valley has been filled with up to 800 feet of margin flanking the Jocko Hills, appear to be median of 20 gpm (figure 2). are distributed unevenly across the map, and map of the Cordilleran ice sheet, Mission Valley Aquifers are saturated geologic materials that proglacial deposits and lacustrine sediments of completed in Tertiary sediments. Reported well accuracy is greater near points of measurement. Montana: Ph.D. dissertation, University of yield sufficient water to supply wells and springs. glacial Lake Missoula. The subsurface yields range from 1.0 up to 400 gpm with a Dayton valley Well locations are accurate to the 2.5-acre level Colorado, Boulder, 191 p. Non-aquifer materials (also known as confining stratigraphy is a complicated sequence of silt, median of 15 gpm (figure 2). The Dayton valley is a relatively small, northwest- (+/- about 300 feet). Land-surface altitudes at beds) also may be saturated, but have low clay, sand and gravel deposits. Ground water in trending intermontane basin about 6 miles long well locations were interpreted from U.S. Makepeace, S. V., 1994, Hydrogeologic permeability and do not produce usable amounts the Mission valley occurs in discontinuous layers Ground water generally occurs under unconfined and less than 2 miles wide. The valley's Geological Survey (USGS) 1:24,000 topographic framework for principal valley fill aquifers: of water to wells or springs. The permeable layers of permeable sand and gravel that are separated conditions. Ground-water flow follows the surface topography has been shaped by glacial features. maps and are generally accurate to +/- 5 to 10 ft Flathead Indian Reservation, Montana: CSKT of sand and gravel that form most of the aquifers by low permeability layers of lacustrine silt and topography to the northwest, gradients are steeper The arc-shaped ridge on the northwest part of (based on 10 and 20 ft contour intervals). The Natural Resources Department, 13 p. are composed of alluvium (silt, sand, and gravel clay. Most of the permeable layers are buried at in the southern part of the valley and along the the valley dams Lake Mary Ronan, and is the potentiometric surface contour intervals are either most likely deposited by glacial meltwater depths greater than 75 feet below the land surface. valley margins. terminal moraine of the Dayton Lobe of the 50 or 100 feet, depending upon the valley. The Slagle, S. E., 1988, Geohydrology of the Flathead streams), and are covered and/or interfinger with Locally, shallow sand and gravel also may support Flathead glacier. The broad valley surface slopes potentiometric contours are expected to be Indian Reservation, northwestern Montana: glacial till (poorly sorted clayey gravel deposited surficial aquifers at depths less than 75 feet below Little Bitterroot valley toward Flathead Lake and is covered by till, accurate to within one-half of the contour interval U.S. Geological Survey Water-Resources directly by glaciers), and glaciolacustrine deposits land surface, the most notable examples being The Little Bitterroot valley is a northwest-trending glaciolacustrine deposits and meltwater alluvium. (+/- 25 ft, or +/- 50 ft depending on the valley). Investigation Report 88-4142, 152 p. (clay and silt deposited in glacial lakes). The the alluvium associated with Mud Creek near intermontane basin that is bounded by the Salish The valley is drained by the southeast-flowing depth, continuity, and character of these Pablo and the area between Post and Mission Mountains on the east and north, and the Cabinet Dayton Creek and its tributaries. Belt bedrock ACKNOWLEDGMENTS Smith, Larry N., 2002a, Geologic framework of permeable layers vary from valley to valley Creeks (Smith, 2002b; Makepeace, 1994). Mountains to the west. The southeast flowing of the Salish Mountains surrounds and underlies Well owners who allowed collection of the data the southern part of the Flathead Lake Area, reflecting the variable depositional history of Although the permeable units are generally not Little Bitterroot River and its tributaries drain the valley; some Tertiary deposits (reported on necessary for the map, and the people who Lake, Sanders, and Missoula Counties, each valley. contiguous over large areas (Slagle, 1988) there the valley. The valley-fill deposits consist of fine- drillers logs as "light gray rock" or "soft gray collected the data are all gratefully acknowledged. Montana: Montana Bureau of Mines and is sufficient hydraulic continuity between the grained, Tertiary sandstone, siltstone and clay rock") may overlie the bedrock. At the crest of Reviews of this report by Tom Patton, Wayne Geology Ground-Water Assessment Atlas 2, The Belt Supergroup bedrock, which occurs sand and gravel layers to be considered a single that are overlain by a layer of Pleistocene sand the moraine the valley-fill deposits may be up Van Voast, improved its clarity. part B, map 10, scale 1:100,000. around the fringe of the valleys, generally contains entity in terms of ground-water flow on a valley- and gravel that varies from as little as 7 to as to 700 feet thick, but are generally less than 300 sufficient fracture permeability (the primary wide scale. much as 60 feet in thickness. The sand and gravel feet thick in other parts of the valley. SOURCES OF DATA Smith, Larry N., 2002b, Thickness of shallow openings through which water moves in the rocks layer, which is capped by 200 to 350 feet of Geographic Features: alluvium, Flathead Lake Area, Flathead, Lake, are fractures or "cracks") to yield water to wells This map presents the potentiometric surface for lacustrine silt and clay, forms what is informally Records from GWIC indicate that there are at Population centers and roads are from 1:100,000- Sanders, and Missoula Counties, Montana: and is included as part of the valley-fill aquifers the ground-water flow system in the Mission referred to as the Lone Pine aquifer (Donovan, least 84 wells completed in the valley. Wells scale USGS Digital Line Graph files available Montana Bureau of Mines and Geology because it appears, based on the potentiometric Valley; although data are presented from wells 1985). Shallow alluvial gravels, thin sand lenses supply domestic, stock and public water supplies. from the Natural Resources Information System Ground-Water Assessment Atlas 2, part B, surface(s), to be in hydraulic communication completed at various depths, more weight was within the lacustrine deposits, and fractured About half the wells are completed in the Belt (NRIS) at the Montana State Library, Helena, map 11, scale 1:100,000. with the valley-fill deposits. It should be noted, given to those completed at depths greater than bedrock also supply water to wells, however bedrock but the rest of the wells are completed Montana. Hydrography has been simplified from that ground water in the Belt bedrock occupies 75 feet below the land surface when contouring. ground water from the Lone Pine aquifer supplies in surficial sand and gravel (mostly near Flathead the 1:100,000 Digital Line Graph files. Township Smith, L., LaFave, J., Carstarphen, C., Mason, and moves through fractures and voids within Ground-water flow is generally away from the most of the domestic, stock and irrigation water Lake), and in alluvium buried by various amounts boundaries are from the U.S. Forest Service. The D., and Richter, M., 2002, Data for water the rock, rather than through intergranular spaces Mission Mountains, which serve as the major in the valley (Abdo, 1997). of lacustrine silt and clay, and/or till. Well depths land ownership base was modified from wells visited during the Flathead Lake Area as in the sand and gravel deposits. Because of recharge area, westward toward the Flathead are as much as 622 feet with a median of 227 1:100,000-scale land ownership data available ground-water characterization study: Flathead, the irregular distribution of fractures within the River. North of the Polson moraine, ground water The potentiometric surface portrayed on the map feet (figure 1). Most reported yields are relatively from NRIS. Lake, Sanders, and Missoula Counties: bedrock, ground-water occurrence in the bedrock flows towards Flathead Lake. The Moiese and is based on data from wells completed in the low, and the median reported yield is 12 gpm Montana Bureau of Mines and Geology can be unpredictable, and well yields can vary Valley View Hills, which are bedrock highs, Lone Pine aquifer and wells completed in the (figure 2). Ground-water flow is away from the Point Data: Montana Ground-Water Assessment Atlas 2, widely between locations. divert ground-water flow in the western part of fractured bedrock. Water-level data from Abdo valley margins and to the southeast toward Well-location and water-level altitude data were part B, map 1, scale 1:250,000. the valley; ground-water flow from the north (1997) collected in 1993 and 1994 were used to Flathead Lake. obtained by Ground-Water Characterization The potentiometric surface represents the altitudes part of the valley converges toward lower Crow supplement data collected by the Ground-Water Program and personnel from the Confederated Thompson, W.R., 1988, Hydrogeology of the to which water will rise in wells penetrating an Creek, while ground-water flow in the southern Characterization program. Ground water in the Camas Prairie basin Salish and Kootenai Tribes; altitudes of the points Jocko Valley, west-central Montana: M.S. aquifer. Ground water moves down the slope of part of the valley converges toward lower Mission Lone Pine aquifer is under artesian conditions The Camas Prairie basin is a small north-trending were determined from USGS 1:24,000 thesis, University of Montana, Missoula, the potentiometric surface, from higher altitude Creek. with flowing wells common in the center of the graben bounded by normal faults on the east and topographic maps. All point data used on this 82 p. to lower altitude, perpendicular to the contours. valley near the Little Bitterroot River. Ground- southwest (Kendy and Tresch, 1996). The valley map are available from the Ground-Water This map shows the potentiometric surfaces of Records from the Montana Bureau of Mines and water flow is away from the valley margins is broad, about 6-miles wide, and flat in its middle Information Center (GWIC) at the Montana Tuck, L.K., Briar, D.W., and Clark, D.W., 1996, the valley-fill aquifers based on water-level Geology's Ground-Water Information Center toward the center of the valley and the Little but narrows to less than a mile wide on its Bureau of Mines and Geology, Montana Tech of Geologic history and hydrogeologic units of measurements from the summer and fall of 1996 (GWIC) data base show that of about 1,900 wells Bitterroot River. What is striking about the southern end. The valley is surrounded by the The University of Montana, Butte, Montana. intermontane basins of the northern Rocky (Smith and others, 2002). In most of the valleys, completed in the Mission valley with reported potentiometric surface in the Lone Pine aquifer Salish and Cabinet Mountains, and is drained by Lake level altitudes were obtained from USGS Mountains, Montana and Idaho: U.S. the potentiometric surface generally reflects the well depths, approximately 1,400 (roughly 74 is the relatively flat hydraulic gradient. The the south-flowing Camas Creek. Belt bedrock 1:24,000 topographic maps. Geological Survey Hydrologic Investigations percent) are completed at depths greater than 75 ground-water altitude decreases only 150 feet surrounds and underlies the valley. The valley- Atlas HA-738-A, scale 1:750,000. T 17N ( 400 400 2897 2942 2814 2943 2943 2819

2828 300 300 2870 J 2859 o 2924 c 2831 k 3010 Well Depth Well 200 200 o 3100 3000 2935 Jocko Valley

2962 100 100 2968 3200 3047 2988 3046 3534 0 0 3033 R Mission Valley Jocko Valley Little Little Dayton Valley Swan Valley Camas Prairie ive 3095 (n = 1894) (n = 567) Bitterroot Bitterroot (n = 81) (n = 93) (n =68) 3136 r Lone Pine bedrock 3015 3094 (n = 220) wells 3158 3035 (n = 73) Arlee 3089 3299 3168 Figure 1. Summary of well depths. 3139 3045 3135 3251 T 16N 3261 3546 3133 3200 3164 Sanders County 3300 Lake County 3190 (95th percentile = 700 gpm) (95th percentile = 500 gpm) Missoula County 300 3348 300 3225 3400 3383 3500 3600 3700 3800 250

3464 3790 200 200

3722 150 3676

3900

100 100 Well Yields (gpm) Yields Well 3922 3931 T 15N 50

3957 0 0

3925 00’ 114 Mission Valley Jocko Valley Little Little Dayton Valley Swan Valley Camas Prairie 3926 (n = 1,670) (n = 516) Bitterroot Bitterroot (n = 76) (n = 88) (n =61) 3968 Lone Pine bedrock 3964 (n = 182) wells (n = 67) Figure 2. Summary of well yields.

R 20W R 19W