Environmental Setting of the Yellowstone River Basin

Table 16. Lithologic, water-yielding characteristics, and water quality of major geologic units in the Yellowstone NAWQA Study Unit Area that lie within the Wind River, Bighorn, and Powder River Basins

(Table modified from Plafcan and others, 1995; Plafcan and Ogle, 1994; Plafcan and others, 1993; and Lowry and others, 1993)
[m, meters; m/d, m per day; mg/L, milligrams per liter; µg/L, micrograms per liter; L/min, liters per minute; yields: small, less than 190 L/min; moderate, 190-1,900 L/min; large, more than 1,100 L/min; --, no data]

System	Series	Geologic unit	Lithology	Water-yielding characteristics	Water quality	Basins where geologic units are present
Quaternary	Sequence in table does not indicate position relative to other Quaternary entries	Alluvium and colluvium	"Unconsolidated clay, silt, sand, and gravel; includes terrace, flood-plain, and pediment deposits along major streams."^1, 2 "Silt, sand, and gravel, unconsolidated; underlies flood plains and bordering terraces."² "Clay, silt, sand, and gravel in flood plains, fans, terraces, and slopes."³	Yield small to large supplies of water; large yields could be developed in some areas.^{1, 2}	"The chemical quality of water in alluvial deposits differs from place to place, depending on the source and amount of recharge, and type of bedrock underlying the alluvium. Water in the flood-plain deposits of perennial streams is generally good in the upper reaches of the stream, but the quality deteriorates downstream."¹ Water in alluvium near Bighorn Mountains is better quality than water in alluvium in central part of Powder River Basin.²	Wind River, Bighorn, Powder River
Quaternary	Sequence in table does not indicate position relative to other Quaternary entries	Dune sand and loess	"Unconsolidated fine to very fine sand; present in eastern part of the Wind River Basin."¹	"Yields small supplies of water of suitable quality for stock or domestic use; it is an important source of water in areas underlain by the Cody Shale."¹ Unknown in Bighorn and Powder River Basins.	Water is of good quality in Wind River Basin.¹ Unknown in Bighorn and Powder River Basins.	Wind River, Bighorn, Powder River
Tertiary	Oligocene	White River Formation	"White to pale-pink blocky tuffaceous claystone and lenticular arkosic conglomerate." Present in the southeastern part of the Wind River Basin.¹	"Highly permeable and productive water-bearing unit. Good intergranular permeability and porosity. Well yields generally range between 4 to 1,100 L/min, with maximum reported production 3,200 L/min. Saturated thickness ranges between 60 to 110 m."⁴ Present as isolated remnants in southwest Campbell County (Pumpkin Buttes), otherwise absent from Powder River Basin within the study unit.³	Dissolved-solids concentrations of historical water samples taken in the Wind River Basin ranged from 207 to 397 mg/L. The water was a calcium carbonate type.	Wind River, Powder River
Tertiary	Eocene	Tepee Trail Formation⁵	"Green and olive-drab hard and generally well bedded andesitic conglomerate, sandstone, and claystone."³	"Yields minor amounts (less than 38 L/min) of water to springs and shallow wells along outcrop. Confining layer."⁴	Limited water quality data (three samples) showed that dissolved-solids concentrations ranged from 197 to 244 mg/L.	Wind River
Tertiary	Eocene	Aycross Formation¹⁷	"Brightly variegated bentonitic claystone and tuffaceous sandstone, grading laterally into greenish-gray sandstone and claystone."³	"Would probably yield at least small, and possibly large, supplies from sandstone and conglomerate beds"¹ "Confining layer."⁴ Localized water yield primarily a function of sandstone content. Sandstone presence highly variable both vertically and laterally.	Unknown.	Wind River, Bighorn
Tertiary	Eocene	Wagon Bed Formation	"Green and gray tuffaceous claystone, sandstone, and conglomerate; some uranium-phosphate marlstone and variegated bentonitic claystone. Locally contains oil shale between Wind River and Bighorn Basins."³	"Yields water locally to springs and shallow wells. Yields less than 38 L/min. Saturated zones include sandstone and conglomerate lenses... Not considered an aquifer."³	Dissolved-solids concentrations of historical water samples taken in the Wind River Basin ranged from 207 to 572 mg/L. The water was a calcium-sodium carbonate type.	Wind River
Tertiary	Eocene	Wasatch Formation	Locally derived conglomerate around Wind River Basin margins. Lower part is Paleocene.³ Drab sandstone and drab to variegated claystone; numerous coal beds in lower part of Powder River Basin.³	Yields water from lenticular sandstone, and to a lesser extent from jointed coal and clinker beds. Yields can be expected to range from 10 to 190 L/min in north part of Powder River Basin becoming generally greater southward with 1,900 L/min or more possible in south part of basin.² Unknown in Wind River Basin.	Dissolved-solids concentrations of historical water samples taken in the Powder River Basin ranged from less than 200 to more than 8,000 mg/L, but commonly ranged between 500 and 1,500 mg/L. Sodium sulfate and sodium bicarbonate were the dominant water types.² Unknown in Wind River Basin.	Wind River Powder River
Tertiary	Eocene	Wind River Formation	"Variegated claystone and sandstone; lenticular conglomerate."³	"Large supplies have been developed in the Riverton and Gas Hills areas and could be developed elsewhere, especially along the margin of the basin. Yields small supplies to many widely distributed stock and domestic wells"^1, 6 Major aquifer in Wind River Basin. "Yields water to wells and springs throughout basin."⁴ Yields range between 4 to 11,000 L/min. Locally contains artesian zones with sufficient head to produce 760 L/min. "Principal source of domestic and stock water on Wind River Reservation. Principal source of industrial water in southern part of basin"⁴	Dissolved-solids concentrations of historical water samples taken in the Wind River Basin ranged from 248 to 5,110 mg/L. The water was a sodium-calcium sulfate type. One water sample analyzed for specific trace elements contained a selenium concentration of 58 mg/L, which is above the Maximum Contaminant Level of 50 mg/L set by the U.S. Environmental Protection Agency.	Wind River
Tertiary	Eocene	Indian Meadows Formation	"Series of variegated claystone, argillaceous sandstone, massive limestone, and poorly sorted conglomerate."⁴	"Confining layer."⁴	Unknown.	Wind River
Tertiary	Eocene	Willwood Formation	Variegated, interbedded claystone and channel sandstone. Averages about 25 percent sandstone.	Might yield enough water from sandstones for domestic or stock use.	Dissolved-solids concentrations of historical water samples taken in the Bighorn Basin ranged from 232 to 9,000 mg/L.	Bighorn
Tertiary	Paleocene	Fort Union Formation	Conglomerate, sandstone, shale, and carbonaceous shale in lower part of formation grading into very fine grained clastics in upper part, present at depth throughout most of the Wind River Basin.¹ Northwest and central Wyoming--brown to gray sandstone, gray to black shale, and thin coal beds.³ "Conglomerate, sandstone, shale, siltstone, and carbonaceous shale in basal part of unit; grades upward to very fine-grained clastics."⁴	Sandstones yield small supplies of water that is generally unsuitable for domestic use and may be marginal for stock in Wind River Basin.¹ "Conglomerate and sandstone zones yield water to wells. Highly productive and permeable where fractured. Water is semi-confined to confined with sufficient head to produce 38 L/min... Basal part of unit is considered a regional confining unit. Upper part of unit contains complex series of permeable and confining layers."⁴ Yields water from fine-grained sandstone, jointed coal, and clinker beds. Maximum yields are about 570 L/min in Powder River Basin.² Might yield enough water from sandstones for domestic or stock use in Bighorn Basin.	Historic water quality data from two samples taken in the Wind River Basin had dissolved-solids concentrations of 994 and 5,110 mg/L. Dissolved-solids concentrations of historical water samples taken in the Bighorn Basin ranged from 623 to 4,890 mg/L. Samples taken in the Powder River Basin ranged from about 200 to more than 3,000 mg/L, but commonly range between 500 and 1,500 mg/L. Water was mostly sodium bicarbonate, and to a lesser extent sodium sulfate.²	Wind River, Bighorn, Powder River
Cretaceous	Upper Cretaceous	Lance Formation	"North Wyoming--thick-bedded buff sandstone and drab to green shale; thin conglomerate lenses.... Northeast Wyoming--brown and gray sandstone and shale; thin coal and carbonaceous shale beds."³	"No known wells produce water solely from unit. Wells completed in Fort Union and Lance Formations. Unit is highly productive and permeable in Big Horn basin (yields range between 4 to 380 L/min)... Large development potential in Wind River Basin."⁴ Generally yields less than 76 L/min, but yields of several hundred liters per minute may be possible from the complete section of the formation in Powder River Basin.²	Dissolved-solids concentrations of historical water samples taken in the Bighorn Basin ranged from 591 to 1,860 mg/L. Dissolved-solids concentrations of historical water samples taken in the Powder River Basin ranged from about 200 to more than 2,000 mg/L, but commonly ranged between 500 and 1,500 mg/L. No dominant water type was prevalent.² Unknown in Wind River Basin.	Wind River, Bighorn, Powder River
Cretaceous	Upper Cretaceous	Fox Hills Sandstone	"Light-colored sandstone and gray sandy shale containing marine fossils."³	Maximum yields in west part of Powder River Basin will probably be less than 380 L/min.²	Dissolved-solids concentrations of historical water samples taken in the eastern Powder River Basin were generally less than 1,000 mg/L, but generally ranged between 1,000 and 2,000 mg/L in west part. No dominant water type was prevalent.²	Powder River
Cretaceous	Upper Cretaceous	Meeteetse Formation	"Chalky-white to gray sandstone, yellow, green, and dark-gray bentonitic claystone, white tuff, and thin coal beds."³	Sandstones yield small supplies of water that is generally unsuitable for domestic use and may be marginal for stock in Wind River Basin." "Regional confining layer."⁴ Sandstone might yield enough water for domestic or stock use in Bighorn Basin.	Dissolved-solids concentrations of historical water samples taken in the Bighorn Basin ranged from 936 to 2,920 mg/L. Unknown in Wind River Basin.	Wind River, Bighorn
Cretaceous	Upper Cretaceous	Lewis Shale (Bear Paw Shale)	"Gray marine shale containing many gray and brown lenticular concretion-rich sandstone beds."³	Sandstones yield small supplies of water that is generally unsuitable for domestic use and may be marginal for stock in Wind River Basin.¹ Sandy zones may yield as much as 38 L/min, but most of the formation does not yield water in Powder River Basin.²	Unknown.	Wind River, Bighorn, Powder River
Cretaceous	Upper Cretaceous	Mesaverde Formation	"Light-colored massive to thin-bedded sandstone, gray sandy shale, and coal beds."³	Permeable and productive water-bearing unit. Regional aquifer. Well yield data not available; however, artesian flows reported in numerous petroleum tests in central Wind River Basin.⁴ Yields of as much as 190 L/min are possible from sandstone beds, and as much as 760 L/min where fracturing has increased the permeability, generally near geologic structures.²	Dissolved-solids concentrations of historical water samples taken in the Wind River and Bighorn Basins ranged from 688 to 5,510 mg/L. The water type was variable. Dissolved-solids can be expected to range from about 300 to more than 2,000 mg/L in the Powder River Basin. Most water will be sodium sulfate type.²	Wind River, Bighorn, Powder River
Cretaceous	Upper Cretaceous	Cody Shale	"Dull-gray shale, gray siltstone, and fine-grained gray sandstone."³	Yields only meager supplies of poor quality water in Wind River Basin.¹ "Regional confining layer."⁴ Yields of as much as 76 L/min possible from sandstone beds, but other rocks in formation would yield little or not water in Powder River Basin.² Thin sandstone might yield enough water locally for domestic or stock use in Bighorn Basin.	Dissolved-solids concentrations of historical water samples taken in all three basins ranged from around 700 to over 8,000 mg/L. The water was a sodium sulfate type in the Bighorn and Powder River Basins.	Wind River, Bighorn, Powder River
Cretaceous	Upper Cretaceous	Frontier Formation	"Gray sandstone and sandy shale."³	Yields small quantities of generally poor quality water although some supplies are usable for domestic purposes in Wind River Basin."¹ Upper two-thirds of unit is regional aquifer in Wind River Basin; lower one-third of unit is confining layer. Water is under confined conditions with sufficient head to produce flows of 38 to 95 L/min at selected petroleum tests. Yields 19 to 570 L/min to shallow stock and domestic wells"⁴ Yields of as much as 190 L/min are available from sandstone beds in Powder River Basin.² Artesian conditions exist in the area along Kirby Creek in the Bighorn Basin.	Dissolved-solids concentrations of historical water samples taken in the Wind River and Bighorn Basins ranged from 280 to 9,960 mg/L. The water type was variable. Dissolved-solids can be expected to range from about 300 to more than 3,000 mg/L in the Powder River Basin. Most water is sodium bicarbonate or sodium sulfate type.²	Wind River, Bighorn, Powder River
Cretaceous	Upper Cretaceous	Mowry Shale	"Silvery-gray hard siliceous shale containing abundant fish scales and bentonite beds."³	Regional confining layer in Wind River Basin.⁴ Some of these rocks may yield as much as 38 L/min, but most of the formation does not yield water in Powder River Basin.² Might yield very limited quantities of water to wells where fractured in Bighorn Basin.	Historic water quality data from one sample taken in the Wind River Basin had a dissolved-solids concentration of 648 mg/L. Dissolved-solids concentrations of historical water samples taken in the Bighorn Basin ranged from 362 to 1,150 mg/L. Unknown in Powder River Basin.	Wind River, Bighorn, Powder River
Cretaceous	Lower Cretaceous	Thermopolis Shale	"Black soft fissile shale; Muddy Sandstone Member at top."³	Regional confining layer in Wind River Basin.⁴ Ground-water possibilities not known in Powder River Basin, but probably poor.² Shales are relatively impermeable. Wells developed in Muddy Sandstone Member may yield enough water for domestic or stock use in Bighorn Basin.	Historic water quality data from two samples taken in the Wind River Basin had dissolved-solids concentrations of 223 and 525 mg/L. Dissolved-solids concentrations of historical water samples taken in the Bighorn Basin ranged from 599 to 1,100 mg/L. Unknown in Powder River Basin.	Wind River, Bighorn, Powder River
Cretaceous	Lower Cretaceous	Cloverly Formation	North Wyoming--"rusty sandstone at top, underlain by brightly variegated bentonitic claystone; chert-pebble conglomerate locally at base. Northeast Wyoming--rusty to light-gray sandstone containing lenticular chert-pebble conglomerate interbedded with variegated bentonitic claystone."³	"Yield small to moderate supplies of water suitable for domestic use near outcrops"¹ Permeable and productive upper and basal sandstones in Wind River Basin. Water is under artesian conditions with sufficient head to produce flows of 4 to 95 L/min at selected petroleum tests. Yields water to stock wells along outcrops.^{4, 6} Most yields range from 19 to 76 L/min in the Powder River Basin, but yields of 380 L/min or more are possible from complete section of rocks, and as much as several hundred liters per minute from zones of secondary permeability.² Sandstones might yield enough water for stock or domestic use in Bighorn Basin.	Dissolved-solids concentrations of historical water samples taken in all three basins generally ranged from 300 to 3,000 mg/L. Sodium sulfate was the dominant water type in the Powder River Basin.²	Wind River Bighorn Powder River
Jurassic		Morrison Formation	"North Wyoming--dully variegated claystone, nodular limestone, and gray silty sandstone. Northeast Wyoming--dully variegated siliceous claystone, nodular white limestone, and gray silty sandstone"³	Sandstones may yield enough water for domestic or stock use.	Dissolved-solids concentrations of historical water samples taken in the Wind River Basin ranged from 798 to 1,710 mg/L. Historic water quality data from one sample taken in the Bighorn Basin had a dissolved-solids concentration of 673 mg/L. Unknown in Powder River Basin.	Wind River Bighorn Powder River
Jurassic		Sundance Formation	"Greenish-gray glauconitic sandstone and shale, underlain by red and gray nonglauconitic sandstone and shale."³	"Yield small to moderate supplies of water suitable for domestic use near outcrops"¹ Regional aquifer in Wind River Basin. Large intergranular permeability in sandstone and chert lenses. Yields water to shallow stock and domestic wells along outcrops (4 to 95 L/min).⁴ Sandstone beds in Powder River Basin will probably yield no more than 76 L/min.² Sandstones might yield enough water for stock or domestic use in Bighorn Basin.	Dissolved-solids concentrations of historical water samples taken in the Bighorn Basin ranged from 331 to 1,750 mg/L. Dissolved-solids can be expected to range from about 500 to more than 2,000 mg/L in the Powder River Basin. No water type is dominant.² Unknown in Wind River Basin.	Wind River Bighorn Powder River
Jurassic		Gypsum Spring Formation	"Interbedded red shale, dolomite, and gypsum. In north Wyoming wedges out south in T. 39 N."³	No water wells known to tap this formation in the Wind River Basin, but it would probably yield only poor quality water.¹ "Regional confining layer."⁴ Solution zones in gypsum beds yield small amounts of water in Bighorn Basin.⁷ Yields a few liters per minute locally for stock purposes from solution cavities in or near outcrop areas in the Powder River Basin.²	Historic water quality data from one sample taken in the Wind River Basin had a dissolved-solids concentration of 1,360 mg/L. Dissolved-solids concentrations of historical water samples taken in the Bighorn Basin ranged from 287 to 2,650 mg/L. Dissolved-solids are generally greater than 1,000 mg/L in the Powder River Basin, the dominant water type is calcium sulfate.²	Wind River Bighorn Powder River
Jurassic(?)-Triassic(?)		Nugget Sandstone	"Gray to dull-red crossbedded quartz sandstone."³	"Water-bearing potential not known in Wind River Basin, but probably would yield small supplies, and larger supplies might be developed in some areas"¹ Water-yielding characteristics unknown in Bighorn Basin.	Historic water quality data from one sample taken in the Wind River Basin had a dissolved-solids concentration of 1,470 mg/L. Unknown in Bighorn Basin.	Wind River Bighorn
Triassic		Chugwater Formation	"Red siltstone and shale. Alcova Limestone Member in upper middle part in north Wyoming. Thin gypsum partings near base in north and northeast Wyoming."³	Yields small supplies of good quality water in and near outcrops in Wind river Basin.¹ Will probably yield as much as 76 L/min in Powder River Basin.² May yield sufficient quantities of water to wells for domestic and stock use in the Bighorn Basin.	Dissolved-solids concentrations of historical water samples taken in the Wind River and Bighorn Basins ranged from 251 to 2,940 mg/L. The water type was calcium sulfate. Dissolved-solids generally range from about 500 to more than 1,000 mg/L in the Powder River Basin, the dominant water type is calcium sulfate.²	Wind River Bighorn Powder River
Triassic		Dinwoody Formation	"Olive-drab hard dolomitic thin-bedded siltstone."³	Yields small supplies of good quality water in and near outcrops in Wind River Basin.¹ Water-yielding characteristics unknown in Bighorn Basin.	Yields small supplies of good quality water in and near outcrops in Wind River Basin.¹ Unknown in Bighorn Basin.	Wind River Bighorn
Triassic and Permian		Goose Egg Formation	"Red sandstone and siltstone, white gypsum, halite, and purple to white dolomite and limestone."³	Probably would yield only small supplies of mineralized water in Wind River Basin.¹ Yields little or no water in Powder River Basin.² Might yield small quantities of water to wells as a result of dissolution of gypsum in Bighorn Basin.	Dissolved-solids concentrations of historical water samples taken in the Bighorn Basin ranged from 205 to 2,230 mg/L. Unknown in Wind River and Powder River Basins.	Wind River Bighorn Powder River
Permian		Phosphoria Formation and related rocks	"Brown sandstone and dolomite, cherty phosphatic and glauconitic dolomite, phosphatic sandstone and dolomite, and greenish-gray to black shale."³	"Complex series of permeable sandstones and impermeable limestone, dolomite and siltstone. Highly productive where fractured. Well yields range up to 3,800 L/min"⁴ Yields as large as 3,800 L/min observed in Bighorn Basin.	Dissolved-solids concentrations of historical water samples taken in the Wind River and Bighorn Basins ranged from 215 to 3,690 mg/L. The water type was variable.	Wind River Bighorn
Permian and Pennsylvanian		Tensleep Sandstone	"North Wyoming--white to gray sandstone containing thin limestone and dolomite beds. Permian fossils have been found in the topmost beds of the Tensleep at some localities in... Owl Creek Mountains."³	Uppermost unit of the Tensleep aquifer system. Good intergranular permeability, excellent permeabilities where fractured. Saturated throughout Wind River Basin. Water is under confined conditions with sufficient head to produce flows of 4 to several hundred L/min from selected wells.⁴ Yields ranging from 76 L/min to as much as several hundred L/min are possible from these rocks, and where fracturing has increased the permeability, yields greater than 3,800 L/min may be possible in the Powder River Basin.^{2, 8} Flowing wells along the western flank of the Bighorn Mountains yield large dependable supplies of water.	Dissolved-solids concentrations of historical water samples taken in the Wind River and Bighorn Basins ranged from 171 to 3,480 mg/L. The water type was calcium-magnesium carbonate in the Wind River Basin. "Dissolved solids commonly range from 200 to 500 mg/L and are generally less than 1,000 mg/L, but locally may be more than 2,000 mg/L."²	Wind River, Bighorn, Powder River
Pennsylvanian and Mississippian		Amsden Formation	"North Wyoming--red and green shale and dolomite; at base is brown sandstone."³	Part of Tensleep aquifer system. Sandstone member is permeable along joints and partings between bedding planes. Excellent permeabilities where fractured. Water is confined. Well yields range between 4 to several hundred L/min in Wind River Basin.⁴	Unknown.	Wind River, Bighorn, Powder River
Mississippian		Madison Limestone or Madison Group	Massive to thin bedded limestone, containing some thin beds of chert and red shales near the top.¹ "Massive crystalline limestone and dolomite with siltstone and shale zones, cherty in places."⁷ "Dolomite and limestone, massive to thin bedded, cavernous in upper part"²	Part of Tensleep aquifer system. Poor permeabilities except where fractured. Some saturated caverns. Water-bearing throughout Wind River Basin. Water is confined. Well yields range between 4 to several hundred L/min.⁴ Yields of more than 3,800 L/min are available where cavernous and fractured zones are present in Powder River Basin.² Unit in hydraulic connection with underlying Bighorn Dolomite forming the Madison-Bighorn aquifer in Bighorn Basin.	Dissolved-solids concentrations of historical water samples taken in all three basins ranged from 169 to 3,390 mg/L. Water type in Powder River Basin was sodium sulfate. One sample in the Wind River Basin was a calcium-magnesium carbonate water type. One sample in the Bighorn Basin was a calcium sulfate water type.	Wind River, Bighorn, Powder River
Devonian		Darby Formation	"Yellow and greenish-gray shale and dolomitic siltstone underlain by fetid brown dolomite and limestone."³	"Part of Tensleep aquifer system. Generally considered a confining layer, but permeable along joints and fractures. Numerous joint controlled springs along Wind River Mountains."⁴ May hydrologically separate the overlying Madison Limestone from the underlying Bighorn Dolomite.	Unknown.	Wind River, Bighorn
Ordovician		Bighorn Dolomite	"Gray massive cliff-forming siliceous dolomite and locally dolomitic limestone."³	"Basal part of Tensleep aquifer system. Basal sandstones are permeable; also permeable along joints and fractures. Yields water to numerous springs along Wind River Mountains."⁴ Yields ranging from 76 L/min to several hundred liters per minute should be available from solution cavities and fractures in Powder River Basin.² In combination with the Darby Formation and the Madison Limestone, forms the Madison-Bighorn aquifer in the Bighorn Basin, which produces large and dependable supplies of potable water.⁷	Historic water quality data from two samples taken in the Wind River Basin had a dissolved-solids concentration of 102 and 178 mg/L. Dissolved-solids concentrations of historical water samples taken in the Bighorn Basin ranged from 196 to 3,440 mg/L. Unknown in Powder River Basin.	Wind River, Bighorn, Powder River
Cambrian		Gallatin Limestone	"Blue-gray and yellow mottled hard dense limestone."³	"Confining layer. Permeable along joints and fractures. Yields small quantities (less than 19 L/min) to springs along the Wind River Mountains."⁴ Probably yields less than 38 L/min in Powder River Basin.^2, 9 In combination with underlying Gros Ventre Formation, forms a confining layer for the Flathead Sandstone in Bighorn Basin.	Historic water quality data from one sample taken in the Bighorn Basin had a dissolved-solids concentration of 296 mg/L. The water type was magnesium bicarbonate. Unknown in Wind River and Powder River Basins.	Wind River, Bighorn, Powder River
Cambrian		Gros Ventre Formation	"Limestone, shale, and calcareous shale, flat-pebble conglomerate at base."⁴ "Green-gray thin-bedded limestone and limestone-pebble conglomerate."	"Ground-water possibilities not known, but rocks are potential sources of large supplies where fractured or cavernous."¹ "Confining layer."⁴ Probably would yield less than 38 L/min in Powder River Basin.^{2, 10} Thin sandstone beds indicate potential for small yields in Bighorn Basin.	Unknown.	Wind River, Bighorn, Powder River
Cambrian		Flathead Sandstone	"Dull-red quartzitic sandstone."³	Major aquifer in Wind River Basin. Permeable along partings between bedding planes, faults, fractures and joints. Small interstitial permeabilities. Water is semi-confined to confined. Yields 4 to 19 L/min to shallow stock and domestic wells. Excellent ground-water resource potential; however, relatively undeveloped because of availability of shallower ground-water sources.⁴ Yields of 76 L/min are probably available in the Powder River Basin.^2, 11 Yields over 7,600 L/min reported in Bighorn Basin.⁷	Dissolved-solids concentrations of historical water samples taken in the Wind River and Bighorn Basins ranged from 37 to 443 mg/L. Three samples from Hot Springs County in the Bighorn Basin were a calcium bicarbonate water type. Unknown in Powder River Basin.	Wind River, Bighorn, Powder River

¹Whitcomb and Lowry, 1968.
²Hodson and others, 1973.
³Love and Christiansen, 1985.
⁴Richter, Jr., 1981.
⁵Part of the Absaroka Volcanic Supergroup.
⁶Includes Morrison Formation.
⁷Libra and others, 1981.
⁸Includes Amsden, Hartville, and Minnelusa Formations.
⁹Includes Whitewood Dolomite, Winnipeg, and Gros Ventre Formations.
¹⁰Includes Whitewood Dolomite, Winnipeg, and Gallatin Formations.
¹¹Includes Deadwood Formation.

Table 17. Shallow Hydrogeologic Units in the Powder River Basin, Montana and Wyoming

(Table modified from Lewis and Hotchkiss, 1981)
[m, meters; L/min, liters per minute]

Hydrogeologic Unit	Range of Thickness (m)	General Description	Water-Yielding Characteristics
Wasatch-Tongue River aquifer	0-1,190	Includes interfingering lenses of gravel, sand, silt, and clay of alluvium or terrace deposits (not shown on map) near the major streams and their tributaries; tuffaceous bentonitic claystone and siltstone which grade downward into lenticular fine-grained sandstone of the White River Formation; brownish-gray fine- to coarse-grained lenticular sandstone, interbedded with shale and coal, weathering to a buff color and the clinker deposits near coal outcrops of the Wasatch Formation; light-yellow to light-gray fine- to medium-grained thick-bedded to locally massive cross-bedded and lenticular, calcareous sandstone and siltstone, weathering to a buff color, thick and laterally persistent coal beds, and clinker deposits near coal outcrops of the Tongue River Member of the Fort Union Formation; and may contain light-gray fine- to medium-grained sandstones and siltstones of the upper part of the Lebo Shale Member of the Fort Union Formation	Yields range from 19 to 380 L/min for alluvium and from 10 to 610 L/min for sandstone, coal, or clinker deposits; most wells are shallow in the upper part of the unit. In the southern part of the basin yields as much as 1,900 L/min may be possible from sandstone or clinker deposits with proper well construction; well yields of 38-190 L/min have been measured. Wells completed in the lower part of the aquifer may flow as much as 38 L/min. Unit is an aquifer everywhere clinker deposits exist in the saturated zone
Lebo confining layer	0-920	Dark shale predominates with interbedded light-gray and brown to black carbonaceous shale, siltstone, and locally thin coal beds of the Lebo Shale Member of the Fort Union Formation. Altered and devitrified volcanic ash and brown ferruginous concretions are present in shale	Functions as a retarding layer within the study area; may yield as much as 38 L/min to wells locally where sufficient saturated thickness of lenticular channel deposits is penetrated
Tullock aquifer	0-600	Includes light-gray fine- to medium grained channel sandstone near the base of the Lebo Shale Member where present plus light-gray sandy or silty shale, locally resistant sandstone which grades downward into interbedded medium-gray to light-gray shale, light-gray fine-grained sandstone and siltstone, and thin coalbeds of the Tullock Member of the Fort Union Formation	Yields from fine-grained sandstones and jointed coal beds may be as much as 150 L/min but yields of 57 L/min are more common. Where aquifer is confined, wells generally flow less than 38 L/min
Upper Hell Creek confining layer	0-610	Interbedded gray to brown siltstone and shale, locally lenticular fine- to medium-grained sandstone, and interbedded claystone, thin coal beds, silty sandstone, and bentonitic shale of the upper part of the Hell Creek (or Lance) Formation	Limited water supply in study area; functions as a major retarding unit. Locally, flowing wells tapping sandy deposits yield as much as 15 L/min
Fox Hills-Lower Hell Creek aquifer	0-780	Interbedded carbonaceous shale, sandy shale, siltstone, and claystone with local deposits of gray to brown silty to clayey often crossbedded sandstone of the lower part of the Hell Creek (or Lance) Formation plus the marine gray to light-tan fine- to medium-grained sandstone of the Fox Hills Sandstone; locally contains thin beds of sandy shale	Yields as much as 760 L/min to properly constructed wells, with yields generally less than 380 L/min. Reliable source of water for artesian wells; wells flow as much as 76 L/min along major river valleys

Table 18. Hydrogeology of southeastern Montana

Hydrogeologic Unit	Range of Thickness (m)	General Description	Water-Yielding Characteristics
Alluvial aquifer	2-40	Includes lake-basin deposits, unconsolidated flood-plain deposits, and adjacent terrace deposits less than 15 m above current stream level--Largely unconsolidated sand, silt, and clay with local lenses of gravel. Coarse well-rounded gravel interbedded with finer material is common in basal alluvial deposits along the Yellowstone and Missouri Rivers, probably derived from reworked terrace gravels.	Coarse gravels along the Missouri River are reported to yield as much as 1,900 L/min to large-diameter wells; along smaller streams and adjacent low-lying terraces, yields of 380 L/min might be possible. Yields average about 57 L/min to stock and domestic wells.
Terrace gravel aquifer	2-30	Comprises terraces of Crane Creek, Cartwright, Flaxville, and Rimroad Gravels as described by Howard (1960)--Mostly gravel and sand with some silt and clay. Well-rounded 25- to 300-mm-diameter cobbles and boulders and sand-size particles of quartzite, chert, and igneous rocks are common. Deposits are largely distributed along upland areas and benches of the Yellowstone river. Many of the higher deposits are covered by loess.	Terraces are mostly isolated, topographically high units having limited saturation. Yields may be as much as 76 L/min to domestic and stock wells centrally located within larger deposits and along major streams at lower altitudes.
Wasatch-Tongue River aquifer	1-880	Consists mostly of Tongue River Member of Fort Union Formation but locally includes overlying basal rocks of Wasatch Formation--Light-gray to brownish-gray fine-to medium-grained thick bedded to massive and locally crossbedded lenticular calcareous sandstone and siltstone. Commonly weathers light yellow to buff. Contains light-buff to dark-gray shaly siltstone and shale, brown to black carbonaceous shale, and coal beds as thick as 25 m.	Sandstone and coal beds are the major water-yielding units in the study area; shales do not yield water. Yields are as much as 610 L/min to wells penetrating thick saturated sections. However, average yields to most stock and domestic wells are less than 76 L/min. Where saturated, fractured clinker beds may yield as much as 250 L/min to wells.
Lebo confining layer	0-180	Includes Lebo Shale Member of Fort Union Formation--Predominantly dark shale interbedded with light-gray and brown to black carbonaceous shale, siltstone, and locally thin coal beds. Shales contain altered and devitrified volcanic ash and reddish-brown ferruginous concretions. White to light-gray argillaceous crossbedded and lenticular sandstones occur locally.	Relatively large percentages of lowly permeable shale in this unit retard vertical movement of water. However, in local areas where saturated, medium-grained channel sandstones may yield as much as 95 L/min to wells.
Tullock aquifer	0-180	Comprises entire thickness of Tullock Member of Fort Union Formation and locally includes upper 3 to 24 m of Hell Creek Formation--Interbedded medium-gray to light-gray shale, light-gray fine-grained sandstone and siltstone, and thin but persistent coal beds. A resistant sandstone commonly forms a rimrock at the top of the unit. Locally, sandstones and siltstones weather yellow to brown.	Fine-grained sandstones and coal beds are the water-yielding units. Well yields may e as much as 150 L/min, but generally average about 57 L/min. Flowing wells tapping confined aquifers generally yield less than 38 L/min.
Lower Fort Union aquifer	0-170	Includes rocks in eastern part of study area equivalent to Lebo and Tullock Members of Fort Union Formation and may include uppermost part of Hell Creek Formation--Mostly interbedded light-gray to dark-gray shale, siltstone, and shaly sandstone. Upper part of unit is mostly shale; locally interbedded with lenticular siltstone and sandstone that commonly weather yellow to tan color. Lower part contains a few thin lignite coal beds. Overall appearance is darker than overlying and lighter than underlying units. Contact is conformable and generally transitional with underlying unit.	Shaly sandstones and coal beds are the water-yielding units. Typical well yields are 45 L/min. Locally, because of low permeability, the entire aquifer can retard vertical movement of water.
Upper Hell Creek confining layer	0-180	Comprises upper part of Hell Creek Formation--Gray to yellowish-gray silty clayey carbonaceous and bentonitic shale and siltstone; locally contains yellowish-gray to tan fine- to medium-grained silty sandstone, thin coal beds, and brown ferruginous concretions.	Limited as a water supply in the study area; a few flowing wells yield about 19 L/min. Generally a low permeability unit.
Fox Hills-Lower Hell Creek aquifer	0-230	Includes lower part of Hell Creek Formation and Fox Hills (Lennep) Sandstone--Gray to yellowish-gray to tan fine- to medium-grained sandstone; contains gray to olive-gray shale and shaly siltstone. Locally has massive or crossbedded sandstone layers and thin coal beds near top of unit. Lower contact considered to be the middle of the transitional siltstone located between sandstone above and shale of underlying unit. Contact is conformable with underlying unit.	Significant source of water in the study area. Yields 76 L/min to flowing wells along major streams valleys, where conditions permit. Yields as much as 260 L/min to domestic and stock wells and 760 L/min to municipal or industrial wells.
Bearpaw confining layer and older rocks, undifferentiated	0-340	Bearpaw confining layer consists of Bearpaw Shale and equivalent upper part of Pierre Shale; forms the base of the overlying shallow aquifer system--Bearpaw is gray to black marine shaly claystone and shale; thin beds of siltstone, silty sandstone, and bentonite occur locally.	Very low permeability; generally does not yield water to wells in the study area.

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