Montana Ground-Water Assessment Atlas No. 2, Part B, Map 6 December 2004 Montana Bureau of Mines and Geology A Department of Montana Tech of The University of Montana Surficial Geologic Map of the upper Flathead River valley (Kalispell valley) Area, Flathead County, Northwestern Montana by Larry N. Smith Note - this map was originally published at a scale of 1:70,000 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, which has a shaded topographic base, 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 114o 37 30 48o30 R22W R23W R24W Qgo Qgt Qao Qgt Qaf Ybe Qgo Qgt Qgl 69 Ybe Ybe Qlk Qgt Qlk Qgt Ybe Qgta Qgo Ybe Qgt Qal Ybe Qgt Qal Qgo Qgo Qgt Ybe Qgt Qgt Qgo Qgt Ybe Qlk Qgt Qaf Qgt Qgi Qgt Qgo 68 QTs Ybe Qgl Qgo Qgo Ybe Qgo Qgt Qgl Whitefish Qgi 78 76 Qgo Qgi Qgi Ybe Qgl Qgt Qgl Qgt Ybe Qal 72 Qgo 75 Qgl Qgi Qgt Qgo Qgi Ybe Qgo Qaf Qgi Qgo Qgo 66 e Lak lly Ta Qgt Qgt 73 74 Ybe Qgl Qlk Ybe Qal Ybe Ybe Qgt Qgo Qgt Qgt Qlk Qal Qgt W Qgt ke h La efis hit 70 Qaf Qgo Ybe Ybe Ybe Qal Qlk 71 Qaf Qaf Ybe Qgt Qgt Ybe Qgo Qal T31N Ybe Qgt Qgo T32N R21W Ybe Qal Qgo Qaf Qgl Qlk Qgta Qgi Qge 77 Qgt Qgl 79 Qgl Qe Qgl 35 Ground-Water Assessment Atlas No. 2, Part B, Map 6 December 2004 114o R19W R20W Qal Qgta Qao Qgt Qao Ybe Qgt Tk Qgt Qls Qao Qgt Ybe Qls Ybe a Qls Qgoo 21a 83 Qgt Ybe Qgo 28 21 Ybe Qgt Qgo Qgo Qgi Qal Qaf Qgta Qgta Qgls Qgo Qgl Qgt Lake or reservoir 5 Qgt Qao Qgo Hungry Horse Columbia Falls Qgo Marsh Qgo Qe Qe Qgt Qao Qgo 32 80 Qal 33 34 Qgo Qgoo Ybe Qao Qgo Qaf Qao Qaf 31 Qaf Qgt Qaf Ybe Qgt Population center T31N Qgo Qaf Qgo Township boundary, section boundary Qgta Tk Qgo Qgl 81 Qaf Qal Qgta Road Tk Tk Tk Qls 23 22 27 24 Qgt 26 25 Qgo Qgoo Qgo Tk 84 Qls Qgo Stream 82 Qgo Qgta Contact, dashed where approximate Qgo Qls Qls Key to Symbols Qgt Qal Ybe T32N Qgo Ybe Qgo Ybe Qgta Qal Qgt Ybe Qgt 48o30 Qgt Location where geologic notes were recorded, photographs taken, and/or a vertical section was described. GLACIOFLUVIAL CHANNEL - Channelized depressions recognized from aerial photographs and topographic expression; associated with deposits of glacial outwash in some areas; multiple types of channels are represented: ice-marginal channels: irregular linear erosional channels formed by channelized flow next to, or partially beneath the lateral margins of glaciers; commonly form notches, meander loops, and some integrated drainage networks in bedrock or till that then may have become modern streams; some contain series of internally drained depressions (pools formed by scour). Abandoned alluvial channels: channel traces in unconsolidated deposits that show the positions of abandoned distributary channels across outwash. Paleoflood channels: channels formed predominantly in bedrock or till formed by catastrophic releases of water. CREST OF DEPOSITIONAL LANDFORM - Ridgetops of landforms formed on Pleistocene or Holocene sediment; multiple types of landforms are represented: Drumlins and moraines: mostly oriented parallel to glacier-flow directions, in till deposits; Kames: conical and elongate ridges, in ice-contact deposits; Disintegration ridges: elongate, sinuous and intersecting ridges, in ablation till (Gravenor and Kupsch, 1959; Flint, 1971; Goldthwait, 1975); Eolian dunes: crests of stabilized dunes, in eolian sand; Debris-flow levees: ridges formed parallel to margins of debris flows, rare in ablation till and ice-contact deposits in areas of high relief. SCALE 1:70,000 Universal Transverse Mercator Projection Qlk Qgt 67 Qgt Ybe Qgt Qgo Qgt Qgo Ybe Qgt Qgo Qgta Qgt Ybe Qgl Qgo Qao Qgt Qgta Ybe Qgo Qgt Qgo Qe Qgt Qgo st C re Qgo Ybe ek Ybe Qal Qgt Qe Qgl Qe Qe Ybe Qgt Qgt Qal Qgt Qal Qgi Ybe Qgt Qgt Qgo Qgta Ybe Ybe T28N Qgi Qgi 89 Qgo Qgt Qgo Qgi Qgi Qao Qgo Ybe Qgt Qao Qgi Q Qgl Qgo Qgls Qgt Qgt Qgo Qgl Ybe Qgt Qao Qgi 90 Qgi Qgi Ybe Qao Qgta Qgt Ybe Qgl Qao 65 Qgt Qgt Ybe Qgo Qgi Qgi Qgo Ybe Qgl Qe Qgi Qgt Qgo Qe Qgl Qgt R23W Qe Qe Qe Qgi Ybe Qe Qe Qgta Qgt Ybe Qe Qgo Qgo R24W Qgo Qge Qgt Qgo Qao Qe Qgt Qgl Qgt T29N Qao Qge Qgt Qgt Ybe Q Qao Qgt Lo Qgo Qgt Qgo Qaf Qgl 36 Qe Qe Qgta Qgo Qgo Qgl Qgta 46 Qgi thea d Qgo Ybe Fla T30N Qgta Qgo Qgt Qgo Qgl Whitefish River Qgo Qgt Ybe r Ri v e ater llw Sti Qgo Qgo Qao Qgl Kalispell Qgl Qgi Qgl Qgls Qgl Qao T30N Qao Qgo Qgta 29 Qaf Qao 44 43 42 19 20 18a Qls 18 Qao 40 41 45 39 Qao Zone 11 Datum NAD27 30 Hu Ho ngry Res rse erv oir Correlation of Units Alluvium Eolian Alluvial Fan Landslide Lacustrine Till and Ice Contact Deposits Deposits Deposits Deposits and Outwash Deposits Qal Qgl Qgo Qgi Qao Qgi 85 Qao 86c Qgo Rive r Qgt Qgo Eocene Miocene unconformity Belt Supergroup Middle Proterozoic Ybe Qgt 14 Qgi Qal T29N Qlk Qgl Qgt Qgo Qgta Qgi La Qgl ke Qgi Qgt Bl ai Qgi ne Qaf Qe Qgi 10 Qgl 11 QTs ? Qaf Qe Qgt Qgo Qgls Qgl Pleistocene Tk Qgt 13 Qgi Qao Qgi Qge 12 Qgi Qe Qgta unconformity Kishenehn Formation Qaf Qgi Qgi Qgl Qgt Qgt 17 Qaf 16 Qgi Qgt Qgl Qgls Holocene Qaf 15 Qgt Qlk Qls Qgoo 86b Qe Qaf Qgl 86a 87 88 Qgo Qe Qgt Qgta 86 Qgi Qgt Qgt Qao Qaf Qgi Qaf Qgi Qgo Qe Qgt Ybe Qaf Qal Qgt Qgt Qgi Ybe Qgta Qaf Qgta Qgo Qgls Qgi 8 8a Qao 7 Qgi 9 Qgls Qgo Qgo Qgi Qgo Qgi Qgi Qgi Qgi Qaf Qgo Qe Qgta Qaf T28N Qge Qgi Qge Qgo 6 Qgt Qgo Qal Fo yL Ybe Qgta Ybe ak Ybe Qgi Qao e Ybe Qgta Ybe Qgo Qal Ybe Qao Ybe Ybe Ybe Qgo Ybe Ybe 48o0730 Description of Map Units Qal Qaf Qe Qlk Qls Ybe Qlk T27N Ybe R23W Ybe Ybe Qgo R22W 114o30 ALLUVIUM OF MODERN CHANNELS AND FLOODPLAINS (Holocene) - Light to medium brown and grayish brown sand and silt, and lesser amounts of pebbles, cobbles, and clay along active stream valleys and areas of sheetwash; contains minor amount of colluvium along the bases of steep slopes; thicknesses average 30 feet, but reach 90 feet in paleochannels south and southeast of Kalispell; ground water commonly near land surface; produces significant quantities of water. ALLUVIAL FAN DEPOSIT (Holocene) - Grayish brown and light to dark yellowish brown sand, silt, pebbles, cobbles, and boulders deposited in fan-shaped landforms downslope from canyon mouths; thicknesses range from 1 to 60 feet; ground water commonly near land surface; locally produces water. Qgt Qao Ybe Ybe T27N EOLIAN DEPOSIT (Holocene) - Dark to light yellowish brown fine and very fine-grained well sorted sand deposited as eolian dunes and sand sheets; grains mostly of quartz with common argillic or calcareous rock fragments; pebble-sized clasts of argillite, quartzite, and weakly consolidated siltstone occur as rare particles in deposits and locally as layers on or near the ground surface; a distinctive bed of white to very pale orange volcanic ash (Glacier Peak ash, dated at 11,200 14C yr; Carrara, 1995) occurs within or near the base; bedding is massive where the unit is thin, but wind-ripple cross-laminations and large-scale sandflow cross stratification are common in thicker deposits; the deposit is truncated near stream courses by alluvium; soils occur at the surface and buried within the deposit; dune forms are poorly preserved due to modification during stabilization and post-depositional erosion; thickness ranges from 1 to 40 feet; water table is typically below the unit, but the unit may be saturated seasonally; not known to produce significant quantities of water. Ybe LAKE DEPOSIT (Holocene) - Mostly calcareous silt, clay, and organic debris deposited in perennial and ephemeral lakes; includes minor amounts of sand and gravel; distribution of unit inferred beneath lakes and marshes; thickness unknown, but likely 1-30 feet; ground water commonly near land surface; not known to produce water. ALLUVIUM, OLDER (Holocene) - Light to dark brown and grayish brown sand, pebbles, cobbles, and minor silt and clay; upper surface forms terraces near major stream valleys; topographic position intermediate between active stream valleys and areas of outwash deposition; thickness ranges from 1 to 40 feet; ground water commonly near land surface; produces significant quantities of water. Qgo GLACIAL OUTWASH DEPOSIT (upper Pleistocene) - Light brownish gray and light to dark brown stratified gravel, sand, and silt; clasts of calcareous siltite, quartzite, intrusive igneous rocks, sandstone, and siltstone; well stratified, channelized, and cross stratified with lenticular beds of imbricated cobbles and pebbles; rare boulders and larger clasts indicate ice-rafting; upper surface is broad and even with local closed depressions and abandoned glacio-fluvial channels; thicknesses average 50 feet and are locally more than 140 feet; ground water commonly near land surface; produces significant quantities of water. Qgl GLACIAL LAKE DEPOSIT (upper Pleistocene) - Light yellowish brown, pale brown, and light brownish gray, calcareous fine sandy silt, clayey silt, and minor clay; thin to medium laminations rhythmically alternate between darker-colored clay-rich laminae and lightercolored and thicker silty and sandy laminae; deposit has broad, even surfaces except for few closed depressions; deposited from suspension in pro-glacial lakes formed behind glacial moraines; thicknesses average 100 feet and are locally greater than 270 feet; typically watersaturated, but produces little water to wells. GLACIAL LAKE DEPOSIT, SANDY (upper Pleistocene) - Light yellowish brown fine to medium-grained sand, conglomerate, sandy silt, silt, and minor clay; similar to Qgl, but consists predominantly of sand with lesser amounts of rhythmically laminated clay and silty and sandy laminae; lenticular granule, pebble, and cobble conglomerate locally overlies beds displaying soft-sediment deformation; deposited in nearshore environments in pro-glacial lakes; deposits have broad, flat surfaces and few closed depressions; thicknesses average 50 feet but locally are more than 150 feet; typically water-saturated, but only locally productive to water wells. Qg Ybe LANDSLIDE DEPOSIT (Holocene and upper Pleistocene) - Boulders, cobbles, and pebbles in a light to dark brown matrix of sand and silt; clasts are mostly angular and subangular; deposited by gravity sliding to an area near the base of a hill or mountain slope; surface of unit is typically hummocky and lobate in form; thickness ranges from 1 to 80 feet; ground water commonly near land surface; locally produces water. Qao Qgls Qgo Ybe Y Ybe Ybe Ybe Ybe Ybe T26N Ybe R21W Surficial Geologic Map of the uppe Qgo Qgta Qgo Qgi Qge Qge Qgt Qgo Qao Qgta Qgo Qgo Qal Qgo Qgt 5 Ec Qal ho Qal La Qgta ke Qgi Qgta Qgo Qgi Ybe Ybe Ybe Qlk Qgl Ybe Qao Ybe Qgt Qge Qgi Ybe Qgt Qe 3 Qge 4 2 Ybe Ybe Qgl 62 Qgi Qgt Qal Ybe Qao Flathead Lake Qgo Ybe Ybe QTs Ybe Qgls Qao Ybe Qgt Qls R an iver Sw Ybe Ybe Qgi Qgo Bigfork 59 Ybe T27N 1 Ybe Qlk gl Qao Qgls Qao Qaf Qgt Ybe 60 Qgi Qal Qgo Qgt 61 Qlk Qgt Qgo Ybe Qlk Ybe Qgta T26N Ybe Qgta Qgta 64 64a Qal Ybe Qal Ybe Qao Qgta Ybe Ybe Qgi Sw an Ybe Qgt R19W La ke 48o R18W 113o5230 R20W er Flathead River valley (Kalispell valley) Area, Flathead County, Northwestern Montana by Qgta GLACIAL TILL, ABLATION DEPOSIT (upper Pleistocene) - Granule, pebble, and cobble conglomerate, and lesser amounts of light gray, light brownish gray, pale yellowish brown, grayish orange, and pale brown, compact beds of diamicton and stratified beds of sand; interstratified complex of massive till, poorly bedded ice-contact deposits, and well-stratified drift; formed during disintegration of glacial ice; characterized by knob and kettle topography with some elongated crests of glacial landforms representing crevasse-fills, eskers, and kames; thicknesses range from 1 to 150 feet; although lateral and vertical variations in lithology affect potential for ground-water development, typically produces water to wells in most locations. Qge GLACIAL ESKER DEPOSIT (upper Pleistocene) - Pebbles, cobbles, boulders, and some light to medium brown sand; most clasts are well rounded cobbles; some exposures display horizontal bedding; clasts of grayish black to medium dark gray metacarbonate, argillite, light gray and medium gray bedded quartzite, weathered calcareous mudstone, and distinctive cobbles of dark gray to black basalt (Purcell Lava); forms narrow, sinuous ridges; thicknesses range from 1 to 60 feet; ground-water levels typically below the unit, but the unit may be saturated seasonally; the unit is not known to produce significant quantities of water. (2) Flathead Lake Characterization Study Area er Riv e. Rg Figure 2. Index to previous map compiled: (1) Carrara (1990), ( Witkind (1978a), (4) Witkind (1 an Sw e. Rg METHODS AND DATA SOUR Swan Mission R Polson Moraine Fla the a Key Streams Southern Extent of Pleistocene Glaciers River ge. BELT SUPERGROUP ROCKS , UNDIVIDED (Precambrian Y) - Numerous stratigraphic units composed mostly of siltite, metacarbonate, and quartzite (Johns, 1970; Winston, 1986; Harrison and others, 1992, 1998) and minor amount of igneous rocks (McGimsey, 1985); water wells completed in fractured zones yield adequate supplies for household use. ad the Fla Ybe KISHENEHN FORMATION (upper Eocene-Miocene) - Yellowish brown to orange medium and coarse-grained pebbly sandstone with pieces of carbonized wood fragments, pebble and cobble conglomerate, beds of carbonaceous shale, and light olive gray, dusky moderate yellow, and grayish orange mudstone; conglomerate with silty, sandy matrix, well and moderately rounded clasts of argillite, quartzite, and orange siltstone; horizontal bedding and imbricated fabric; sandstone and conglomerate beds have channelized, erosional bases; mudstones have common scoop-shaped, concave-up fractures; moderately indurated with calcium carbonate cement; calcium carbonate occurs locally as 0.04-0.2" thick rinds on clasts; steeply dipping, cemented fractures in sandstones; about 120 feet of section crops out in steep exposures (Constenius, 1988); water wells completed in sandstone and conglomerate yield adequate supplies of water for household use in a few parts of the northeastern part of the map area and in the valley of the North Fork of the Flathead River. Kalispell o Tk QUATERNARY OR TERTIARY SEDIMENT (Pleistocene or Tertiary) - Pale yellowish orange to grayish orange (dry), moderate to dark yellowish orange (moist) stony clay loam (diamicton); clasts include weathered meta-carbonate and argillite; unit infills wide fractures in Belt Supergroup bedrock and occurs beneath light brown unweathered till in limited areas; diamicton may be either an older till (Stoffel, 1980) or Tertiary debris flow deposits (P. C. Ryan, written comm., 1999); exposed thickness about 30 feet; subsurface distribution and aquifer potential of the unit is poorly known, however its clayey texture suggests the unit is not an aquifer. Libby ah QTs Map Area Id Qgoo GLACIAL OUTWASH DEPOSIT, OLDER (Pleistocene) - Light and medium brown, yellowish brown, and brownish gray granule, pebble, and boulder conglomerate and coarse-grained sand; local calcium carbonate cement; clasts of quartzite and meta-carbonate; trough crossstratified and channelized beds; clasts are imbricated; crops out beneath till in steep exposures in the northeastern part of the map area; exposed thicknesses are about 100 feet (sec 7 DDB, T. 31 N., R. 19 W.); based on its location below till the unit correlates to upper part of the deep aquifer north of Flathead Lake. properties will be combined wit wells and their logs to produce and thickness of aquifers and co Previous mapping of sur (1968) was done for part of the Their depiction of the distribution and alluvium is similar to that o Contacts shown between till and surrounding the valleys were al mapping (fig. 2) and should be Canada ish itef Wh GLACIAL ICE-CONTACT DEPOSIT (upper Pleistocene) - Light to dark brown and brownish gray pebble and cobble conglomerate with lesser amounts of laminated silt and clay, bedded sand, diamicton, and boulder conglomerate; clast lithologies dominated by rounded and subrounded argillite, metacarbonate, and quartzite with minor siltstone, sandstone, fossiliferous limestone, and distinctive cobbles of dark gray to black basalt (Purcell Lava); beds of different lithologies are superimposed and cross cutting, forming complex sequences; softand frozen-sediment rotational and collapse features are common; conglomerates display large- and very large-scale tabular and trough cross-stratification, crude horizontal stratification in a matrix of granules and coarse-grained sand, and clast imbrication; laminated silt and clay sequences are mostly less than a few feet thick and discontinuous in outcrop; sand occurs in cross-stratified, upward-fining beds, and as apparently massive, well-sorted beds with intercalated silt and clay laminae that show collapse structures; diamictons are typically less than a few feet thick and occur as sheet-like bodies and dipping beds apparently deposited by debris flows; forms individual conical and stream-lined hills (kames), flat-topped ridges (kame terraces), and linear deposits (crevasse-fills), and hummocky topography (Gravenor and Kupsch, 1959; Flint, 1971; Goldthwait, 1975); changing proportion of lithologies causes unit to grade into areas mapped as till, ablation deposits, and glacial esker deposits; thicknesses range from 1 to 150 feet; lateral and vertical variations in lithology affect potential for ground-water development in the unit; typically productive to water wells in most locations. The upper Flathead River valley (Kalispell valley) is an intermontane valley north of Flathead Lake that is bordered on the east by the Swan and Mission Ranges, on the north by the Whitefish Range, and on the west by the Salish Mountains. The northern part of the Swan River valley is included in this discussion (fig. 1). The valley is drained by the Flathead River and its major tributaries, the Stillwater and Whitefish Rivers in the northwest, the Swan River in the southeast, and Ashley Creek on the west. Elevations range between 7,528 feet on the crest of the Swan Range to 2,892 feet, the summer pool elevation of Flathead Lake. The areas geomorphology consists of a low-relief floodplain along the Flathead River, that broadens markedly south of Kalispell; flights of terraces along the main river valleys; and rolling uplands above the terraces that contain drumlinoid glacial landforms. The transition to the Swan Range is abrupt along the east side of the valley, whereas, alluvial fan and glaciated surfaces form more gradual footslopes along the Whitefish and Salish mountains to the north and west. Outside of suburban areas, the valley is vegetated by various crops, introduced and native grasses, and deciduous forests in low-lying areas and conifer forests in hilly and mountainous areas. Montana Qgi INTRODUCTION tns. GLACIAL TILL (upper Pleistocene) - Predominately granules, pebbles, cobbles, and boulders supported by a matrix of light gray, light brownish gray, pale yellowish brown, grayish orange, and pale brown, compact sandy or silty loam (diamicton) deposited by active glacial ice; minor amounts of stratified sand and gravel (stratified drift) deposited by flowing water; clast lithologies include light and medium bluish gray metacarbonate, white weathered metacarbonate, fine-grained quartzite, argillite, diorite, and distinctive cobbles of dark gray to black basalt with amygdules filled with white quartz that contains many fluid inclusions, apparently derived from the Purcell Lava of the Belt Supergroup, which is present in Glacier National Park and the Whitefish Range to about 10 miles north of Columbia Falls (Johns, 1970; McGimsey, 1985); clasts typically rounded and subrounded; more resistant clasts are commonly striated; crests of glacial landforms include drumlins and moraines; occurs as a veneer over Belt Supergroup rocks in most mountainous areas; glaciofluvial channels cut across the unit and some of the drumlins and moraines; thicknesses average 90 feet and are locally more than 250 feet; typically water-saturated, but produces little water to wells except from bodies of stratified drift. Salish M Qgt Polson d River Missoula Location BC Alberta Study Area ND WA OR Sask. Montana ID SD WY Figure 1. Index map showing the location, principle roads and cities, drainages, and maximum extent of the last glacial advance. This map shows the distribution of unconsolidated surficial geologic units within the relatively densely populated upper Flathead River valley portion of the Flathead Lake Ground-Water Characterization Study area. Contacts between units with different hydrogeological Mapping was carried ou 1:20,000-scale black and white s hand plotting on 7½-minute top revision was then done. Descrip photographs, and additional field on the map are available from th transferred to mylar, scanned, a The topographic base da (DEMs) available from the Mon System (NRIS). Vertical and ho data cause apparent striping and base data of roads are from NRI Forest Service, Flathead Nationa were digitized at Montana Bure minute quadrangles. GEOLOGIC OVERVIEW The mountain ranges con sedimentary rocks, and a few ig Supergroup which have been th fill in the upper Flathead River v Larry N. Smith th subsurface data derived from water additional maps showing the depth to onfining units. rficial deposits by Konizeski and others study area at a scale of about 1:70,000. n of till, outwash, glacial lake sediments, of this map, although different in detail. d bedrock in the mountainous areas most entirely compiled from previous considered approximate. (1) Map Area ) (3) (4) ps from which some contacts were (2) Harrison and others (1992), (3) 978b). RCES ut by interpretation of 1954-vintage stereo aerial photographs. Contacts were pographic maps. Field checking and ptions of outcrops and vertical profiles, d notes made at numbered field locations he author. The geologic data was and digitized in ArcInfoTM. ata are from digital elevation models ntana Natural Resource Information orizontal linear artifacts in some of the d irregularities in the shading. Digital IS; streams and lakes are from the U.S. al Forest, Kalispell; public land surveys eau of Mines and Geology from 7½- nsist mostly of slightly metamorphosed gneous rocks, of the Proterozoic Belt he sources for most of the sedimentary valley. Younger sedimentary rocks and some intrusive igneous rocks in areas contiguous to the map area also provided some of the sediment for the valley. These bedrock units were faulted and folded during early Cenozoic eastward thrusting (~60 million yr [60 Ma] ). The upper Flathead River valley is part of the southern end of the Rocky Mountain Trench, an asymmetric, fault bounded half-graben in which bedrock strikes northwest and dips northeast. The trench and other northwest-trending valleys were defined during a regional southwest-directed extensional event that followed early Cenozoic eastward thrusting (Constenius, 1996). The sedimentary rocks of the Kishenehn Formation accumulated from 4821 Ma in the valley of South Fork of the Flathead River, in the northeastern part of the map area, and outside the map area in the valleys of the Middle and North Forks of the Flathead River. A period of east-west directed extension beginning in the Miocene (17 Ma) is responsible for north-south trending faulting, which defines the western flanks of the Swan and Mission Ranges (Constenius, 1996). Most of the displacement along these faults took place on the east-northeast side of the upper Flathead River valley. Geophysical profiling suggests there is more than 3,000 feet of Tertiary and Quaternary sediment in the valley (Konizeski and others, 1968). Siltstone, sandstone, and carbonaceous claystone encountered in boreholes in the south half of T. 31 N., R. 21 W. and in the Swan River valley, just southeast of the map area, may be Tertiary basin-fill deposits that have not yet been recognized in outcrop. GLACIAL AND POST-GLACIAL HISTORY The upper Flathead River valley and nearly all of its neighboring mountain areas were covered by glacial ice during latest Pleistocene time (~15,000-25,000 yr); ice thicknesses in the valleys reached about 4,000 feet. Erosion and burial of sediments during the most recent glacial period has hindered documentation of older glacial sequences. Two small exposures of oxidized diamicton, an unsorted deposit in which pebble to boulder-sized clasts are supported in a matrix of sand and silt or clay (Qts) in sec. 6, T. 26 N., R. 20 W. and sec. 33, T. 31 N. R. 22 W., may be either older till (Stoffel, 1980) or Tertiary debris flows (P. C. Ryan, written comm., 1999). Quaternary surficial deposits that cover the valleys are almost everywhere vegetated, but are locally exposed in natural and artificial cuts along stream banks, roads, and in excavations for sand and gravel. The deepest cuts, and most complete exposures occur in the northeastern part of the map area, along the Flathead River between Hungry Horse and Glacier National Park, outside of the upper Flathead River valley. Alluvium beneath till, which may represent outwash of an advancing glacier (Qgoo), is exposed in secs. 7, 8, and 17, T. 31 N., R. 19 W. along the Flathead River upstream of Hungry Horse. Compact till deposited at the base of the Flathead Lobe of the Cordilleran ice sheet is well represented along the Flathead River in T. 31 N., R. 19 W. and in the drumlin field between Whitefish and Kalispell (T. 30 N., Rs. 2122 W.). Most of the surficial geologic units were deposited during and after retreat of the last glacier from the valley. Ice-marginal streams cut channels and conspicuous meander loops into west-southwest-facing flanks of the Whitefish and Swan Ranges and the Salish Mountains. The channels record temporary positions of meltwater channels during the sequential lowering of ice levels in these areas. As the Flathead Lobe retreated northward, till and ice-contact deposits recorded terminal positions where the receding ice remained stable or readvanced briefly. These areas are (1) south and southwest of Kalispell (T. 28 N., R. 21- 22 W.), (2) along the Whitefish River valley west of Columbia Falls (secs. 19-21, T. 30 N., R. 21 W.), (3) in the town of Whitefish (secs. 25, 26, 35, 36, T. 31 N., R. 22 W.), and (4) along the Stillwater River valley between Whitefish and Talley Lake (sec. 31, T. 31 N., R. 22 W. and sec. 36, T. 31 N., R. 23 W.). Wasting, stagnant glacial ice deposited ablation till deposits (Qgta) which has characteristic hummocky topography, such as the intersecting crests of landforms between Echo Lake and Lake Blaine in the east half of T. 28 N., R. 20 W. Generally level surfaces with internally drained depressions south of Lake Blaine (secs 34 and 35, T. 29 N., R.20 W. and secs. 4-5, T . 28 N., R. 20 W.) and northwest of Kalispell (T. 29 N., R. 22 W.) wre produced by outwash depostion near ice blocks. As the ice blocks melted the land surface locally collapsed, forming depressions. A major landslide (Qls) fell westward into the upper Flathead River valley from sec. 26, T. 30 N., R. 20 W., near the north end of the Swan Range while ice remained in what are now neighboring kettle lakes. Till (Qgt) in many areas is directly overlain by laminated glacial lake deposits (Qgl) deposited in a lake dammed behind the Polson moraine (fig. 1). Rotated blocks of glacial-lake sediments (sec. 36, T. 31 N., R. 22 W., and sec. 21, T. 30 N., R. 21 W.) indicate melting and collapse of, or push by, glacial ice in the lakes. Maximum elevation of the lake dammed by the Polson moraine was 3,200 feet, about 300 feet higher than the current Flathead Lake. As the glacial sediment dams were downcut, lake levels receded, streams incised valleys, and outwash derived from glaciers that had retreated to mountainous areas was deposited. Ice-marginal channels and prominent valleys with underfit streams between Talley Lake and the Lost Creek area north of Kalispell are evidence for one or more catastrophic releases of meltwater into the upper Flathead River valley. The pattern of channels cut in bedrock and till suggest that when the glacier terminated between Talley Lake and Whitefish, water was impounded behind an ice dam in the northern Salish Mountains. Release of water caused extensive scouring of bedrock and till, entrenchment of distributary channels, and deposition of the Lost Creek outwash fan northwest of Kalispell (northwestern corner of T. 29 N., R 22 W.) . As the ancestral Flathead Lake receded within the valley, exposed lake, outwash, and till deposits were partially eroded by wind and deposited as eolian dunes and sand sheets, mostly in the central and eastern parts of the valley (T. 29 N., R..21 and 22 W. and T. 29 and 30 N., R. 20 W.). A 1-inch-thick bed of volcanic ash within the dunes (Field location 87, sec. 9, T. 29 N., R. 20 W.) and locally at the base of eolian deposits (Konizeski and others, 1968) was derived from an eruption of Glacier Peak in Washington state (A. Sarna-Wojcicki, USGS, written comm., 1999). The volcanic ash was deposited at about 11,200 14C yr (Carrara, 1995) and dates the time of major eolian deposition. Buried and surficial soils of various stages of development suggest multiple periods of eolian activity. Topography on the base of glacial lake deposits (e.g. Field Location 36, sec. 22, T. 30 N., R. 21 W.) indicates that downcutting along major stream valleys began before lacustrine sedimentation and has continued to the present. Lateral planation by the Flathead River across its floodplain and the formation of stream terraces has dominated Holocene erosion in the upper Flathead River valley. Deposition of sand, gravel, and mud in the modern floodplain of the Flathead River have accompanied a southward progradation of a modern delta into Flathead Lake. ACKNOWLEDGMENTS This map was prepared in conjunction with the Flathead Lake Study of the Ground-Water Characterization Program. Reviews of the manuscript and map by Lex Blood, Tom Patton, Wayne Van Voast, and Ed Deal improved their quality. GIS analysis and processing was done by Bill Myers and Ken Sandau. 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