Montana Bureau of Mines and Geology Montana Groundwater Assessment Atlas No. 5, Part B, Map 2 A Department of Montana Tech of The University of Montana July 2009 Open-File Version Hydrogeologic Framework of the Upper Clark Fork River Area: Deer Lodge, Granite, Powell, and Silver Bow Counties R15W R14W R13W R12W by

S Qsf w Qsf Yb Larry N. Smith a n T21N Qsf Yb T21N R Author’s Note: This map is part of the Montana Bureau of Mines and Geology (MBMG) a n Pz Pz Groundwater Assessment Atlas for the Upper Clark Fork River Area groundwater Philipsburg Valley–Upper Flint Creek g e Pz Qsf characterization. It is intended to stand alone and describe a single hydrogeologic aspect of the study area, although many of the area’s hydrogeologic features are The town of Philipsburg is the largest population center in the valley between the Qsc interrelated. For an integrated view of the hydrogeology of the Upper Clark Fork Area Flint Creek Range and the John Long Mountains. The Philipsburg Valley contains 47o30’ the reader is referred to Part A (descriptive overview) and Part B (maps) of the Montana 0–40 ft of Quaternary alluvial sediment deposited along streams cut into Tertiary 47o30’ Groundwater Assessment Atlas 5. sedimentary rocks of unknown thickness. The east-side valley margin was glaciated . T20N Yb t R during the last glaciation, producing ice-sculpted topography and rolling hills in side oo B kf l Ovando c INTRODUCTION drainages on the west slopes of the Flint Creek Range. Prominent benches between ac la kf k B Blac oo N F T20N tributaries to Flint Creek are mostly underlain by Tertiary sedimentary rocks. kf t– o N KleinschmidtFlat ot e The Upper Clark Fork groundwater characterization area includes Deer Lodge, Outwash deposits in Fred Burr Creek and other drainages are aquifers. Substantial R va iv d Helmville e a r V Granite, Powell, and Silver Bow Counties. The distribution of geologic units shown bouldery sand and gravel downstream from Boulder Creek suggest that these outwash a ll ey POWELL CO. in the main figure (fig. 1) displays the variety of rock types in different parts of the deposits may have resulted from rapid draining of a glacially dammed lake during the N Pz study area. The geologic units have been simplified from more detailed maps (fig. 2). last glaciation (Beaty, 1961, 1965). Where saturated and permeable, basin-fill deposits eva Pz da Rock units were grouped according to rock type and age that correspond to discernable are aquifers. Ga Cr GRANITE CO. rn ee et k aquifers (fig. 3). Ra T19N Qsc C Fo n A la r g v The Upper Clark Fork River area consists of bedrock-cored mountains separating Avon Valley rk k e o n Qsf V intermontane valleys and a few canyons along major streams. Bedrock defines all Drummond a l T19N le valley and canyon margins and crops out within some valleys where basin-fill units The Avon valley is an intermontane valley with a dispersed rural population. The R y ive Qsc have been eroded. The intermontane valleys, such as the Deer Lodge, Philipsburg, valley has 0–30 ft of alluvial and floodplain deposits along major stream channels

J r Flintvalley Creek o Flint Creek, Summit (Butte-Silver Bow), Avon valley, and Blackfoot River valleys resting on hundreds of feet of Tertiary siltstones and sandstones. The Tertiary basin k h e ckfoot R.

e S a r l n B (fig. 4), are structural depressions (basins) in which locally great thicknesses of weakly fill includes light gray, medium-grained poorly consolidated sandstones and granule C a e t l L tt p n Li i indurated Tertiary sedimentary rocks accumulated. As much as 200 ft of unconsolidated conglomerates, claystone, and shale. Tertiary volcanic rocks and Mesozoic, Paleozoic, o l p Rock Creek F h n B sediments at land surface overlie the Tertiary rocks. Many pre-Tertiary sedimentary and Precambrian sedimentary bedrock units border and underlie the valley. Alluvial i g ou r ld

e M e r Deer Lodge Yb rock units present in the study area have been faulted, uplifted, and eroded into remnants sand and gravel along drainages and in Tertiary sedimentary and volcanic rocks are C k o T18N r . e (Fields and others, 1985; Fritz and others, 2007). Valleys and canyons are the primary aquifers; a few wells are completed in fractured bedrock around the perimeter of the u Philipsburg e e n r g areas of human habitation and groundwater development. Separate populated canyon valley. y t C a n T18N urr C e Pz B r. l d t l i Fre a areas are mostly along short segments of the Clark Fork, Blackfoot, and Little Blackfoot n n a i R s l V Rivers, and Flint and Rock Creeks (fig. 4). Blackfoot–Nevada Valley F e

M g Qsc Valley d Qsf

o

Philipsburg o

u Warm S L METHODS AND DATA SOURCES The Blackfoot–Nevada Valley is drained by the Blackfoot River and Nevada Creek; n pri r ng e t s C the communities of Ovando and Helmville are the main population centers. The upper a r. e i Anaconda n D Yb s Yb Geologic maps for the study area were compiled and simplified from sources shown reaches of Nevada Creek, above Nevada Reservoir, are in the northern end of the Avon in figure 2. A description of the rock units and their relation to map units are shown Valley. Basin fill consists of Tertiary sedimentary rocks, glacial till, and outwash ge n Butte T17N Ra Summit valley in figure 3. Contacts between a few units were redrawn so that they were continuous deposits north of the confluence of the Blackfoot River with Nevada Creek. Quaternary a d y across map boundaries. Where detailed mapping was available at larger scales, it was alluvium lines modern stream valleys inset into older deposits. The valley is surrounded

n e l co l T17N a a Qsf generally used instead of regional, smaller scale mapping. New mapping of some by Precambrian Belt bedrock and Tertiary volcanic and intrusive rocks. n v A Timbere d o surficial deposits in the Ovando to Helmville area of the Blackfoot River valley was The Tertiary sedimentary rocks include claystones, siltstones, and sandstones. i 113 00’ v i Butte

D prepared from field visits (fig. 2; L. Smith, unpublished mapping). All geologic maps Geophysical profiles across Kleinschmidt Flat and water-well logs suggest that in this

– Mt. r e were compiled from digitized versions, and simplified using Arc/Info (tm). area, glacial outwash overlies more than 4,000 feet of Tertiary basin fill (fig. 4; Aguirre DEER LODGE CO. k Fleecer c R11W o s. R15W R14W R10W and others, 2000). Tertiary claystones and siltstones exposed throughout the Divide R Mtn nd GEOLOGIC OVERVIEW Blackfoot–Nevada Valley probably have low permeability. Carbonaceous shales with hla Hig Qsf Yb Qsf Qsf Qsc leaf and twig fossils are common. Tertiary sandstones include fine-, medium-, and SILVER BOW CO. Bedrock, as used here for the rocks in the study area, consists of consolidated rock coarse-grained beds in outcrop with a few granule- to pebble-sized beds (McCune, T16N that is hard enough to fracture. Consolidation is caused by cementation, compaction, 2008). The sandstones are likely aquifers in the subsurface; however, the lateral T16N heat, or the growth of interlocking mineral grains, processes known as induration. The continuity of the beds is unknown. Qsf Qsf general distinction is that groundwater mostly travels along fractures through indurated In the northern half of the valleys glacial till predominates. Between ridges of till + Qsc Ts rocks, whereas in weakly indurated to unconsolidated rocks, groundwater can only are pothole lakes, including Browns and Kleinschmidt Lakes; the lakes are expressions Qsf travel through interconnected pore spaces between mineral grains. Significant rates of of shallow groundwater in till and glacial outwash. Glacial outwash, possibly several Figure 4. Index map showing the principal roads and cities, valleys, basins, Yb Qsf drainages, and physiographic locations. Ts groundwater movement in most bedrock units is therefore dependent on the locations hundreds of feet thick, was locally deposited north of the Blackfoot River and especially + Qsf and continuity of fractures, which are mostly related to folds, faults, and joints near the North Fork of the Blackfoot, on Kleinschmidt Flat (Roberts and Waren, 2001; ++ + (commonly related to cooling and uplift of igneous rock). Highly to moderately Aguirre and others, 2000). Qsf Qsc Qsf + + + ++ Qsc indurated rocks include: Archean gneiss and metasedimentary rocks of the Belt T15N Qsf Qsf Ts ++ Supergroup (combined in the unit “Yb”); Tertiary and Cretaceous intrusive (TKi) and DATA SOURCES + ++ most extrusive (volcanic, TKv) igneous rocks; and Paleozoic sedimentary rocks (Pz). Yb + + + T15N Yb Qsf + Qsf The less consolidated rocks, such as Cretaceous and Jurassic (KJs) sedimentary Original versions of the geologic maps are available through the MBMG and US Qsf + + Qsf ++ + + formations, include sandstones and limestones that are generally less indurated than Geological Survey as attributed in figure 2. Base layers of physiography, hydrography, + + +Qsc ++ Yb Qsf Qsf++++ the older sedimentary rocks, producing water from both intergranular space and townships, and cultural features were derived from Natural Resource Information o Qsf +++ + + + Ts 47 00’ + Ts Scale 1:250,000 fractures. Bedrock is exposed around the valley margins, and is present beneath basin- System datasets. Figure 2. Index to previous maps from which contacts Qsf +++ fill units. Bl + o Ts a Yb + 47 00’ Basin-fill deposits, as defined here, consist of Tertiary sedimentary rocks (Ts) and ACKNOWLEDGMENTS were compiled: ck Yb f + o + Qsf 1. Mudge and Earhart (1983) Ts o unconsolidated deposits. Tertiary sedimentary rocks include claystone, shale, siltstone, t + 0 5 10 15 miles 2. Lewis (1998) T14N R + Yb Yb sandstone, locally thick conglomerate, minor coal and limestone, and volcaniclastic This work was supported by the Groundwater Characterization Program at the i + TKv v e Kleinschmidt Lake units. Within the Tertiary sedimentary deposits are some minor flows of consolidated Montana Bureau of Mines and Geology. The map and text were improved by reviewers, 3. Ruppel and others (1993) Yb r TKi T14N 14 Qsf Montana NAD 1983 volcanic rock. The oldest Tertiary sediments accumulated initially in an early Tertiary including Kirk Waren, John LaFave, John Metesh, Tom Patton, Ed Deal, and Susan 1 4. Lonn and others (2003) Ts+ ckfoot Ts Qsc Browns Lake Bla r State Plane Coordinate System basin that was likely segmented into multiple intermontane basins during the middle Barth. 5. Witkind and Weber (1982) + + Rive 6. Berg (2006) Qsf Yb to late Tertiary (Fields and others, 1985; Rasmussen, 1989; Fritz and others, 2007; Qsf ++ 5 7. Rasmussen (1969) +++ Janecke, 2007). Additional basin fill was deposited during further subsidence of the REFERENCES 6 Qsf + + + Yb intermontane basins. Current streams are removing basin fill. In outcrop, the Tertiary 8. Berg (2005) Ts 7 Yb 11 Qsf+ strata range from unconsolidated to moderately consolidated. Aguirre, E., Gilbert, C., Hatten, M., Kryder, L., Milodragovich, L., Schwennesen, H., 8 9. Portner and Hendrix (2005) TKi Ts Qsf The Tertiary deposits have low permeability in many areas, but can be productive Sterns, S., and Yurek, B., 2000, Geophysical study of Kleinschmidt Flat, Powell 9 10. Gwinn (1961) +++ 13 12 11. Brooks and Sears (in press) Bailey Mtn. T13N + TKi aquifers where permeable sandstones and conglomerates are laterally continuous and County, Montana: unpublished report prepared for Montana Department of Natural Yb Yb ++ Qsc receive sufficient recharge. In many areas Tertiary rocks with low permeability Resources and Conservation, Geophysical Engineering Department, Montana Tech 10 16 12. Brooks and Sears (in press) Griffin Creek Ts + Qsf Ts++ T13N 13. Sears and others (2000) + Qsf ++ (claystone, shale, or siltstone) underlie alluvium, forming a low permeability base to of the University of Montana, 23 p. 15 + a shallow aquifer. Within the Tertiary deposits, geologic maps and subsurface data do Alt, D., 2001, Glacial Lake Missoula and its Humongous Floods: Mountain Press, 14. L.N. Smith (unpubl. mapping) Pz Yb + 15. Derkey and others (1993) R14W TKv + Yb not contain the detail to distinguish packages of coarse-grained aquifer materials from Missoula, 208 p. Yb Ts Yb the fine-grained non-aquifer materials. However, as shown diagrammatically on cross Beaty, C.B., 1961, Boulder deposit in Flint Creek valley, western Montana: Geological 16. Berg (2004) TKi + 4 TKv TKi Qsc R9W R8W section B–B', sufficient subsurface data may allow productive Tertiary aquifers to be Society of America Bulletin, v. 72, p. 1015–1020. 17 2 17. Berg and Hargrave (2004) R15W Yb + Qsc + th 18. Vuke (2004) Yb + locally mapped (fig. 5b). Beaty, C.B., 1965, Flint Creek boulder deposit: Billings Geological Society 16 annual TKv Yb Pz + Ts Unconsolidated basin-fill sediments include sand and gravel- to boulder-sized Field Conference, p. 122–126. + TKv + TKv TKi TKv Yb Ne Qsf T12N + va material (combined on the map as “Qsc”) and clayey and silty gravel and bedded silt Berg, R.B., 2004, Geologic map of the Deer Lodge and Conley's Lake 7.5' quadrangles: da +TKv Pz C Qsc and clay (represented as “Qsf”). Unconsolidated units were deposited both during and Montana Bureau of Mines and Geology Open-File Report 509, 10 p., scale 1:24,000. 18 Qsc Yb re Ts Yb Ts Yb ek + after periods of glaciation. Glaciers occupied higher portions of many mountain valleys Berg, R.B., 2005, Geologic map of the Upper Clark Fork Valley between Garrison and TKv + Ts m TKv Ts + T12N depositing till, mostly gravelly clay and silt that is not an aquifer. Therefore, most of Bearmouth, southwestern Montana: Montana Bureau of Mines and Geology Open- Yb Pz 3 Pz TKv + + Ts the till is mapped as Qsf, except in areas of the Butte 1° x 2° sheet, where it was not File Report 523, scale 1:50,000. + Pz TKv Ts + mapped separately from other Quaternary sediments (Lewis, 1998). Bedded silt and Berg, R.B., 2006, Geologic map of the Upper Clark Fork Valley between Bearmouth R16W Pz Yb TKv clay were deposited in some valleys during stands of Glacial Lake Missoula, a glacial- and Missoula, southwestern Montana: Montana Bureau of Mines and Geology Yb TKv ++ Qsc TKv Pz Pz Pz KJs age lake impounded on the Clark Fork River upstream of the current Montana/Idaho Open-File Report 535, 18 p., scale 1:24,000. +Yb TKi Yb Pz + + Pz Yb Qsc TKi ++ Pz border (Alt, 2001). The lake attained an altitude of at least 4,200 ft, so only covered Berg, R.B., and Hargrave, P.A., 2004, Geologic map of the Upper Clark Fork Valley, + Yb + TKv Pz T11N TKv + + TKv a small portion of the Clark Fork River valley downstream from Drummond. southwestern Montana: Montana Bureau of Mines and Geology Open-File Report C + Qsc ++ KJs lar + er TKv KJs TKv + 506, scale 1:50,000. TKv k+Fork Riv Ts KJs Pz + Pz TKv Pz KJs R18W + + Qsf DESCRIPTIONS OF SELECTED AREAS Brooks, J.A., and Sears, J.W., in press, Preliminary geologic map of the Bailey Mountain R17W Qsc ++ KJs + R7W Yb TKv Ts quadrangle, Powell County, Montana: Montana Bureau of Mines and Geology Pz Pz T11N TKv KJs + Deer Lodge Valley Open-File Report, scale 1:24,000. + + + TKv Pz Yb + ++ Qsc Qsc TKv Brooks, J.A., and Sears, J.W., in press, Preliminary geologic map of the Griffin Creek Qsc Pz + KJs + Pz TKi TKv ++C TKi Pz la KJs The Deer Lodge Valley lies between the Flint Creek Range and the unnamed quadrangle, Powell County, Montana: Montana Bureau of Mines and Geology Ts + r TKv ++Ts Qsc Qsc + k Qsc Pz Qsc mountain range north of Butte. The northern boundary is north of Deer Lodge where Open-File Report, scale 1:24,000. T10N Ts + +F TKv R6W Ts +++ o Ts Yb rk + Ts + the Clark Fork River cuts west through pre-Tertiary rocks, and east of Anaconda where Derkey, R.E., Watson, M., Bartholomew, M.J., Stickney, M.C., and Downey, P., 1993, + Pz Yb TKi Ts + ++ Ri Ts TKi TKv the drainage cut a canyon through volcanic rocks (fig. 4). The valley contains floodplains Preliminary geologic map of the Deer Lodge area, southwestern Montana, revised Ts + ve KJs + r KJs + TKi TKi Pz TKv ++ Pz and terraces along the Clark Fork River and its major tributaries. Above the floodplains May 2004: Montana Bureau of Mines and Geology Open-File Report 271, scale TKi KJs + Ts KJs +Pz + KJs Qsc++ TKv + TKv Yb TKi and terraces are prominent valley-center sloping benches developed on Tertiary basin 1:48,000. +TKi Ts + + Ts Ts + Ts + ++++Ts ++ ++ + Pz fill. The valley margins are bedrock. Fields, R.W., Rasmussen, D.L. Tabrum, A.R., and Nichols, R., 1985, Cenozoic rocks + ++ Ts TKv ot River Ts Ts + Qsc ++ + kfo + + KJs + + + KJs c Qsc Qsc T10N A variety of bedrock units and igneous intrusive and extrusive rocks make up the of the intermontane basins of western Montana and eastern Idaho: A summary, in Pz +++ + ++ la + + + Qsc B ++ Qsc + + +Ts+ Ts +++++ + + TKv mountains and underlie the valley (Konizeski and others, 1968; Rasmussen, 1989; Flores, R.M., and Kaplan, S.S., eds., Cenozoic Paleogeography of West-Central + + + TKv e + + TKi Yb + TKv l TKv + t Ts + + ++KJs t Fritz and others, 2007). The intermontane basin between bedrock outcrops is almost United States: Denver, Rocky Mountain Section Society of Economic Paleontologists T9N Pz++ + + + + TKv i + + Qsc TKi + TKi L + + TKv + + + Ts entirely filled by Tertiary sedimentary rocks, to a depth exceeding 9,000 ft based on and Mineralogists, p. 9–36. Qsc+ Ts TKi +TKi Qsc TKv + Ts + + TKi + + TKv oil and gas exploration wells (McLeod, 1987; figs. 5a,b). The Deer Lodge Valley has Fritz, W.J., Sears, J.W., McDowell, R.J., and Wampler, J.M., 2007, Cenozoic volcanic TKi TKi + + ++ Pz + + Ts Pz+ + the thickest section of Tertiary strata in the Upper Clark Fork River area. Local aquifers rocks of southwestern Montana: Northwest Geology, v. 36, p. 91–110. Yb + TKv + ++ TKi Yb Ts ++ + + KJs ++ TKv + +Pz+ 46o30’ TKi Yb + + TKi KJs in Tertiary rock units include sandstone, pebbly sandstone, and conglomerate. Gwinn, V.E., 1961, Geology of the Drummond area, central-western Montana: Montana Yb + TKi KJs +++ TKv QscTKi m + + Surficial units of Quaternary sand and gravel make up 10- to 70-ft-thick-sequences Bureau of Mines and Geology Geologic Map 4, scale 1:63,360. TKi Ts + + + + + TKi Yb + Yb m +++ KJs ++ Yb+ Pz + + + TKv KJs + in valley bottoms and in broad glacial outwash deposits. Most of the coarse-grained Janecke, S.U., 2007 Cenozoic extensional processes and tectonics in the northern + +++ + KJs Ts ++ TKv Ts Pz Qsf + TKi T9N deposits are on floodplains and adjacent terraces of the Clark Fork River and its Rocky Mountains: southwest Montana and eastern Idaho: Northwest Geology, v. TKi + + Ts Ts TKi TKi TKi + TKv TKv Qsc Qsc + TKi + KJs TKv tributaries. Silty sandy and gravelly alluvial-fan deposits accumulated during the waning 36, p. 111–132. + + Ts TKi Qsf Ts + Qsc Qsc Ts Ts Ts + ++ KJs +TKi stage of glaciation in tributary valleys. Glacial till was deposited by valley glaciers Konizeski, R.L., McMurtrey, R.G., and Brietkrietz, A., 1968, Geology and ground- Ts Pz Ts Qsc Qsc KJs o Pz Pz 46 30’ along the east flank of the Flint Creek Range near the mouths of some side tributaries water resources of the Deer Lodge Valley, Montana: U.S. Geological Survey Water- T8N ++ Pz Qsc + TKi Yb Yb KJs + Yb KJs KJs + KJs TKi to the Clark Fork River. Outwash deposits, coarse-grained alluvium deposited downslope Supply Paper 1862, 55 p. R + Ts Qsc + o + Qsc + from glaciers, are extensive in the Anaconda area (Warm Springs Creek valley) and Lewis, R.S., compiler, 1998, Geologic map of the Butte 1° x 2° quadrangle: Montana c TKi k k e + Pz Pz TKv TKi TKi C re KJs Pz + along other streams in the Flint Creek Range. The coarse-grained surficial deposits are Bureau of Mines and Geology Open-File Report 363, scale 1:250,000. Yb r Ts Pz e C +++ + + TKv e + KJs TKv k Pz significant aquifers. Lonn, J.D., McDonald, C.M., Lewis, R.S., Kalakay, T.J., O'Neill, J.M., Berg, R.B., Ts t + + + TKi in Pz Pz Ts l Pz + TKv and Hargrave, P., 2003, Preliminary geologic map of the Philipsburg 30' x 60' Ts F Pz + TKi Yb Pz Pz + KJs Summit valley and the Divide area quadrangle, western Montana: Montana Bureau of Mines and Geology Open-File Ts ++ Qsc TKv T8N Ts Yb Yb Qsc ++ + KJs Qsc ++ TKv TKi Report 483, scale 1:100,000. TKi Ts Yb Pz Pz +++ Yb TKi Pz + Qsc + + The Summit valley is the headwater of the Clark Fork River; Butte, Montana is McCune, J.G., 2008, Cenozoic sedimentary evolution of the Helmville Basin, west- + KJs Qsc TKi TKv Pz KJs Ts + + Pz Yb +++ + + + Qsc TKi located at its northern end. The adjacent Divide valley between Fleecer Mountain and central Montana: [M.S. thesis] University of Montana, Missoula, 58 p. TKv + + Yb Yb + + T7N TKv Ts Yb + + + + +++ Timber Butte appears structurally and stratigraphically similar to the Summit valley McLeod, P.J., 1987, The depositional history of the Deer Lodge basin, western Montana: Yb ++ + + TKi TKi KJs + Ts ++ Ts Qsc + + (fig. 5c). In the valleys, unconsolidated Quaternary sand and minor amounts of gravel [M.S. thesis] University of Montana, Missoula, 61 p. ++ + Pz +++ TKv + Qsc Yb Pz + Qsc (coarse-grained alluvium) were deposited along stream valleys and as alluvial fans. Mudge, M.R., and Earhart, R.L., 1983, Geologic and structure maps of the Choteau TKv TKi + ++ Ts Yb Ts + Pz KJs Yb + +++ R6W The thickness of unconsolidated Quaternary deposits in both valleys is generally less 1° x 2° quadrangle, western Montana: United States Geological Survey Miscellaneous Yb TKv Yb + Yb ++ Yb + + TKv TKv than 50 ft. However, distinguishing Quaternary from underlying weakly consolidated Geologic Investigation 1300, scale 1:250,000. Ts + Ts + Ts T7N Ts + + Pz TKi + + Tertiary sedimentary rocks using descriptions from most water-well logs is difficult. Portner, R., and Hendrix, M., 2005, Preliminary geologic map of the eastern Flint TKv + Pz A Ts + TKv ++ TKi ++ Qsc TKv Basin-fill deposits are hundreds to thousands of feet thick and rest on Tertiary and Creek basin, west-central Montana: Montana Bureau of Mines and Geology Open- Yb Pz + + + Yb Qsc Ts + A' Cretaceous granitic and volcanic rock (fig. 5c). Most of the basin-fill sediment in the File Report 521, 17 p., scale 1:24,000. Yb Yb Yb KJs ++ Ts Yb + + + Ts Ts + + + + R7W Summit valley is coarse-grained sand derived from disaggregated granitic rock, and Rasmussen, D., 1969, Late Cenozoic geology of the Cabbage Patch area, Granite and Yb TKv ++ Ts Pz ++ + therefore has a texture that promotes indistinct sedimentary layering in surface and Powell Counties, Montana: [M.S. thesis] University of Montana, Missoula, 188 +++ + Pz Pz Ts KJs T6N Yb TKv Ts + Qsc Qsc TKi subsurface lithologic logs. In addition to granitic rock, volcanic rocks with compositions p. Yb TKi Yb Pz TKi Ts Ts + Qsc Yb + r similar to the nearby granite rim the Summit valley. Belt Supergroup bedrock in the Rasmussen, D.L., 1989, Depositional environments, paleoecology, and biostratigraphy Ts + +e ++Yb Ts v + Yb TKi ++ ++i + Highland Mountains forms the southern margin. of Arikareean Bozeman Group strata west of the continental divide in Montana, + + R Ts Ts ++ + TKv Ts TKi Pz k The Tertiary fill of the Divide area is better exposed and better studied than in the in French, D.E., and Grabb, R.F., eds., Geologic Resources of Montana, volume Qsc + + Pz + Ts r T6N Ts Qsc +TKv o Summit valley (Berg and Hargrave, 2004; Vuke, 2004; C. Elliott, unpublished geologic 1: Montana Geological Society Guidebook: Montana Centennial Edition, p. 205–215. + F + + Ts ++ ++ + + TKi + + + Pz Pz ++ + mapping). In addition to granitic rocks, bedrock in the mountains surrounding the Roberts, M., and Waren, K., 2001, North Fork Blackfoot River hydrologic study: Yb Yb + + Ts k Qsc Ts + KJs + TKv TKi + ar Divide area includes volcanic and sedimentary rocks, which causes the basin fill to be Montana Department of Natural Resources and Conservation Report WR-3, 38 p. TKi + l +Pz TKi + + C Ts + + + relatively fine-grained compared to that of the Summit valley. The Tertiary units are Ruppel, E.T., O'Neill, J.M., and Lopez, D.A., 1993, Geologic map of the Dillon 1° x ++ Ts + + Yb + Ts + Qsc

Qsc + +e + TKi + + TKv

Qsc +Ts Yb k TKi Qsc ++ + + dominated by mudstones and fine-grained sandstones. Where saturated with water, a 2° quadrangle, Montana and Idaho: United States Geological Survey Miscellaneous T5N + ++a + Pz Pz Pz + + Ts L + + Qsc + + + TKi + KJs TKv +++ few sheet sandstones and conglomerates and lenticular sandstones in the units are Geologic Investigation 1803-H, scale 1:250,000. n + Qsc + Ts + +w Pz Qsf Yb Ts to Pz + + Ts Qsc aquifers. Sears, J.W., Webb, B., and Taylor, M., 2000, Bedrock geology of Garrison and Luke orge Pz TKv + TKi Ts Yb Ge Pz Pz + R8W Mountain 7.5 minute quadrangle: Montana Bureau of Mines and Geology Open- Yb + +TKi KJs B B' KJs + Ts KJs ++ + + Pz + Ts + + T5N Flint Creek basin File Report 403A, scale 1:24,000. + + +Pz Yb ++ ++ + ++ Qsc Qsc Ts + +KJs +W+ + + Stalker, J.C., 2004, Seismic and gravity investigation of sediment depth, bedrock Yb + Pz KJs +arm + Warm+ Ts Pz Sp+ KJs +++ The valley between the Flint Creek Range on the east and the John Long Mountains topography, and faulting in the Tertiary Drummond-Hall basin, western Montana: Ts KJs Ts rin Ts + Springs TKi Yb Ts + gs TKv ++ m on the west and downstream from Maxville to the confluence of Flint Creek and the [M.S. thesis] University of Montana, Missoula, 63 p. Qsc Pz C Ts Ponds+ Ts + TKi Yb Pz Ts++ +ree + Pz TKv k + Qsc Clark Fork River is known as the Flint Creek basin. Precambrian Belt and Paleozoic Vuke, S.M., 2004, Geologic map of the Divide area, southwest Montana: Montana KJs KJs + m m KJs Pz Yb Ts + bedrock units rim most of the basin; Mesozoic and Tertiary sedimentary rocks crop Bureau of Mines and Geology Open-File Report 502, scale 1:50,000. Yb + T4N Yb Pz Yb Pz m + ++ out on hills east of Flint Creek, and underlie much of the basin. Tertiary sedimentary Witkind, I.J., and Weber, W.M., 1982, Reconnaissance geologic map of the Big Fork- Pz Yb Qsc Pz Pz TKv Ts + rocks of the Cabbage Patch beds and overlying Flint Creek and Barnes Creek beds are Avon environmental study area, Flathead, Lake, Lewis and Clark, Missoula, and Yb Yb ++ + Pz Pz TKi TKi Yb + TKi Yb + + TKv + as much as 2,500 ft thick in parts of the basin and are described in detail by previous Powell Counties, Montana: United States Geological Survey Miscellaneous Geologic + Ts TKi Pz Pz Qsc TKi Yb Yb TKi Pz TKv ++ + workers (Gwinn, 1961; Rasmussen, 1989; Stalker, 2004; Portner and Hendrix, 2005). Investigation 1380, scale 1:125,000. + TKi + Ts + + Yb + Qsc + TKv Pz TKi TKi++ + Ts T4N Unconsolidated Quaternary deposits are aquifers where saturated and permeable. Yb Qsc Creek + + + + Yb ++ Pz Qsc Qsc ill + Ts + Pz TKi M + + TKi + TKv Pz TKi + + + Pz Yb Pz ++ + + ++ R17W Yb TKi ++++++ R18W Pz Pz Qsc Ts ++ TKv + Qsc TKi Yb + Yb TKi Yb Yb Qsc Qsc TKv + ++ ++ ++ Yb Pz TKi + + ++ T3N Yb Qsc Yb + + + o Yb Pz + TKi m 46 00’ Qsc Qsc ++ Pz Qsc TKi + +TKv ++ TKi TKi Ts+ Ts + TKi Yb + + + ++ Yb Ts + Yb + +++ +TKi + + T3N Pz + + + ++ + Qsc Yb Yb ++ + + o Yb TKv + + 46 00’ + + m + + +Qsc+ Pz Qsc + + + + ++ + Yb Ts + + + Yb Pz Yb Qsc + + Yb Ts TKi +TKv + + + ++ TKv TKi Yb + ++ Qsc Yb Yb ++m m +C' R16W TKi Qsc TKv KJs C + + + + Qsc ++ ++ + m + Yb TKv + + + TKi TKi Yb + + + Era – Descriptions of geologic units in which wells were completed. T2N Ts TKv Qsc ++ + TKv Qsc +++ + Eon Ma Period Rock Units Labels Map Units Characteristics Geologic codes (e.g. 112TILL) are those used in the GWIC database. Yb TKi +Qsc TKi TKi Ts + + +++ Ts TKi Ts ++ Qsc TKi + T2N + Quaternary sediments Light to medium brown and grayish brown sand and gravel; Quaternary sediments, coarse-grained + Pz Qsc + + +++++++ alluvium, lake deposits, Qsc + Yb TKv ++++++++ + Quaternary alluvial fan deposits, eolian – coarse-grained some silt and clay; contains minor amount of colluvium; KJs Yb + deposits, talus deposits, glacial Qsc Sandy and gravelly alluvium in recent river valleys. Mostly + + Quaternary sediments thicknesses average 40 ft, but may reach 100 ft thick in TKi + TKi+ + tufa landslide deposits, gravel deposits Qsf gravel and some sand at or near the land surface, deposited by rivers TKi + Pz + Ts 1.8 – fine-grained outwash fans and paleochannels; along active stream valleys B KJs KJs + + + + TKi Qsc TKv i Pz + alluvial fan, terrace, and pediment deposits and glacial meltwater streams; deposits are most notable in the g Yb + + + and areas of sheetwash; groundwater commonly near land R15W TKv R13W Ts Ovando area and beneath Kleinschmidt Flat where they are estimated KJs TKi + surface; produces significant quantities of water; locally Yb KJs upper Tertiary deposits, including: to be between 100 and 500 ft thick (Witkind and Weber, 1982). Ts highly developed by wells for domestic, stock, and irrigation T1N TKi T1N H + + Barnes Creek, Divide, Melrose, Tertiary sedimentary uses. ol + Tucker Creek, and Flint Creek beds rocks – + R12W e + + Sixmile Ts Qsc Pz KJs Creek Fm Quaternary sediments, fine-grained Pz coarse-grained and Grayish brown, light to dark yellowish brown gravelly silt, Ts + KJs + + Qsf Poorly sorted mixture of gravel, sand, silt, and clay deposited Qsc KJs Qsc + T1N Tertiary fine-grained light pink silt and sand, and silty and/or clayey gravel; Rive KJs Qsc Climbing Arrow Formation, thicknesses range from 1 to 300 ft; generally do not produce directly by glacial ice and in other ice-marginal environments + r Pz Ts R6W Cabbage Patch Member, and R14W Pz Qsc TKv Pz Dunbar Member usable amounts of water to wells. (112TILL); some deposits of stratified drift are encased in till; till Qsc KJs Qsc forms prominent moraines in locations along the margins of both + + unconformity Renova Fm + TKi CENOZOIC Tertiary and Yellowish brown to light gray pebbly sandstone, pebble and R11W + TKi Pz Lowland Creek Volcanics, Pz KJs Anaconda the Flint Creek and Anaconda Ranges, but are not shown on this o + Pz Qsc + basalt, andesite, tuff TKv Cretaceous extrusive cobble conglomerate; uncemented to moderately cemented; map; in the Ovando area till overlies and underlies glaciofluvial T1S 113 00’ Qsc + + Fm igneous rocks light tan to gray claystone and siltstone; rare carbonaceous Qsc + TKi Pz KJs Pz Qsc 65.0 Tertiary and shale and lignite; water wells completed in sandstone and and glacial-lake deposits near Kleinschmidt Flat (Witkind and Pz Elkhorn Intrusive rocks: + Yb Golden Butte Quartz ++ Ts Spike Mountains TKi Cretaceous intrusive conglomerate generally yield adequate supplies of water for Weber, 1982); local clay-rich deposits (with varied sand and silt Figure 1. Geologic map of the Upper Clark Fork River area. + Yb Monzonite, aplite, dikes, R10W Pz Fm Volcanics igneous rocks household use; some coarse-grained units in the western content) are of probable glacial-lake origin (112SICL). ++ Qsc Pz sills, and gabbro +++ Qsc Pz Qsc Virgelle Fm Deer Lodge Valley yield hundreds of gpm for irrigation T1S + Qsc TKi T1S Telegraph Creek Fm uses. Tertiary sedimentary rocks Carter Creek Pz +Pz Ts Fm Lithified to unlithified volcanic and volcaniclastic Ts Poorly to well-consolidated; sandstones and conglomerates R7W R6W R5W Jens Fm Ts sedimentary rocks; locally contains sandstone and

Yb Marias

(120SNGR), or claystones, coalbeds, and shales (120SICL); some Coberly Fm River Fm A A' Pz Qsc Cretaceous conglomerate interbedded with flows and tuffs; the rocks sedimentary lithologies are mixed or indeterminate (120SDMS); + + Vaughn Mbr can provide adequate supplies of water for household use. makes up much of the fill in the Deer Lodge, Flint Creek, Philipsburg, Oil and gas well log Ts TKi Ts Taft Hill Mbr White to pink, medium- to coarse-grained granular and Blackfoot–Nevada, and Avon basins. Deer Lodge Valley Pz + Fm porphyritic intrusive rocks; lesser amounts of mafic and

Water well log River Blackleaf Creek KJs + Flood Mbr Ts rhyolitic rocks; where fractured, the rocks can provide Peterson Tertiary and Cretaceous volcanic rocks 6000 Qsc T2S Pz Kootenai Fm adequate supplies of water for household use. Clark Fork + TKv Volcaniclastic rocks, tuffs, welded tuffs; andesitic and basaltic 4000 Pz TKv Cretaceous and flows (mostly unnamed except for the Lowland Creek Volcanics, Qsc R8W 144 124LDCK); the Elkhorn Mountain Volcanics composed of andesitic 2000 Ts + KJs Jurassic sedimentary + + Morrison Fm rocks Tan to brown sandstone and siltstone; gray to reddish shale, and basaltic tuffs, breccias, and flows (211ELKM); some of the 0 +++ Swift Fm siltstone; few gray and reddish conglomerates and gray intrusive rocks may be of Tertiary age. TKi -2000 TKv TKi R9W Jurassic limestone; the rocks can provide adequate supplies of water

MESOZOIC Rierdon Fm -4000 for household and stock uses. Tertiary and Cretaceous intrusive rocks Sawtooth Fm Ellis Gp

TKi Intrusive igneous rocks of compositions ranging from Altitude (ft above sea level) -6000 TKv (a) 206 monzogranite to granodiorite, diorite and gabbro (Lewis, 1998); -8000 Triassic unconformity includes the Boulder Batholith (211BDBT) and the Anaconda and No vertical exaggeration 250 Flint Creek Batholiths (211PLNC). Permian Shedhorn Fm Phosphoria Fm Park City Fm Cretaceous and Jurassic sedimentary and metasedimentary rocks B B' 290 5000 KJs Structurally deformed Mesozoic sandstones, mudstones, shales, TKv Pennsylvanian Quadrant Fm 4000 KJs TKv Ts TKi and minor limestones in mountain areas, around valleys, and 3000 Water well log Altitude underneath basin-fill deposits; metamorphosed where in contact Pz? No Vertical exaggeration 323 Amsden Fm Qsc Quaternary sediments, coarse-grained with the intrusive bodies, as in the western margin of the Deer Big Lodge Basin; includes the Upper Cretaceous Colorado Group Kibbey Fm Snowy (211CLRD) and Golden Spike Formation (211GSPK); and the Tsc Tertiary sedimentary rocks, coarse-grained Mississippian Group 5400 Qsc Ts Lower Cretaceous Blackleaf Formation (217BCKF), Carter Creek Tsf Tertiary sedimentary rocks, fine-grained unconformity Mission Deer Lodge Valley Canyon Fm Formation (217CRCK), the Kootenai Formation (217KOTN), and 5200 Pz Paleozoic Sandstone, quartzite, shale, limestone, and dolomite of Group Lodgepole Fm

Ts Madison TKv various formations; the rocks provide inadequate to minimally undifferentiated sedimentary rocks (217SDMS). 5000 Tertiary and Cretaceous volcanic rocks 354 adequate water to wells for household uses. Three Forks Fm Paleozoic sedimentary and metasedimentary rocks 4800 TKv Lost Creek Qsc TKi Tertiary and Cretaceous intrusive igneous rocks Clark Fork River Devonian Jefferson Fm Pz Structurally deformed Paleozoic limestones, dolomites, 4600 TKi Tsc KJs Cretaceous and Jurassic sedimentary rocks Maywood Fm sandstones, shales, and mudstones in mountain areas, around valleys, 4400 and underneath basin-fill deposits; includes the Permian Phosphoria Tsf PALEOZOIC Pz Paleozoic sedimentary rocks Bighorn Formation (310PSPR), Mississippian Madison Group (330MDSN), 4200 ?? Ordovician Fm KJs 490 Devonian Three Forks and Jefferson Formations (337TRFK, 4000 Ts Tsc Red Lion Fm Altitude (ft above sea level) 341JFRS), and the Cambrian Hasmark Formation (370HMRK), 3800 and undifferentiated Paleozoic (300SDMS) and Cambrian Tsf Figure 5. Geologic cross sections of the (a) Deer Lodge Valley near Deer Lodge, (b) Deer Cambrian Hasmark Fm 3600 ?? (370CMBR) sedimentary rocks. Tsc Lodge Valley north of Opportunity, and (c) Summit Valley and Rocker–Divide valley. Silver Hill Fm 3400 Tsf Flathead Fm 543 Belt Supergroup and Archean rocks TKv unconformity 3200 Pz? intrusion of Yb Metamorphosed limestone, dolomite, siltstone, and sandstone; (b) 10 miles dikes and sills 3000 Pilcher Fm rocks of the middle Belt carbonate (400MCRB), Missoula Vertical exaggeration = 10 Garnet Range Fm (400MSSL), and Shepard (400SPRD) units; and undifferentiated McNamara Fm units of the supergroup (400BELT); these rocks have been folded, C C' Bonner Fm faulted, and fractured; prominent in the Sapphire Range, Flint Creek intrusion Mount Shields Fm 6000 Ts of sills Range, Philipsburg Valley, Rock Creek area, and in the Big Hole Missoula Gp 5000 TKi TKiTs TKi Shepard Fm 4000 River area, and underlying those valleys adjacent to these areas. Altitude Snowslip Fm No Vertical exaggeration Metamorphosed sandstone, shale, siltstone, limestone, and Wallace Middle Belt Proterozoic Belt 6800 Proterozoic Fm carbonate Supergroup and dolomite of various Belt units, minor amount of Archean metasedimentary rock metasedimentary Helena Fm Yb 6600 Piegan Gp Archean gneiss; where fractured, the rocks can provide adequate Rocker–Divide valley Summit valley Empire Fm metamorphic rocks supplies of water for household use. Explanation: 6400 Belt Supergroup 6200 Spokane Fm Study area boundary 6000 expanded Ravalli Gp Qsc scale 5800 Greyson Fm Township boundary Qsc LaHood

5600 PRECAMBRIAN Fm

Blacktail Creek Newland Fm Major road 5400 2500 5200 Archean Gneiss Principal river or stream 5000 TKi Ts TKi Ts TKi

Altitude (ft above sea level) Figure 3. Stratigraphic diagram showing units of original map sources and how 4800 units were combined for this map. Descriptions of map units are generalized Lake or reservoir 4600 from the dominant lithologies. Hydrologic characteristics are generalized from 4400 reported well data in the study area. Intermittent lake, tailings pond, or wetland 4200 (c) Mine land areas 4000 3800 Vertical exaggeration = 10