Geologic units in Carbon county, Montana

Additional scientific data in this geographic area

Quartzofeldspathic gneiss (Archean) at surface, covers 18 % of this area

Quartzofeldspathic gneiss

Tongue River Member of Fort Union Formation (Tertiary) at surface, covers 12 % of this area

Yellowish orange sandstone, sandy and silty carbonaceous shale, and coal. Alluvial plain. Thickness as much as 300 m (984 ft).

Gravel (Quaternary) at surface, covers 8 % of this area

Variable deposits that range from pebble to boulder size and include sand, silt, and clay. Dominantly alluvial terrace, abandoned channel and floodplain, remnant alluvial fan, and local glacial outwash.

Madison Group: Mission Canyon and Lodgepole Formations; or Castle Reef and Allan Mountain Formations (Mississippian) at surface, covers 6 % of this area

Mission Canyon Formation (Mmc): Gray, massive limestone with chert beds and nodules, and solution breccia zones. Shallow marine. Thickness as much as 520 m (1,706 ft). Lodgepole Formation (Ml): Woodhurst Member (upper part of formation): light gray, well-bedded limestone, typically with much dark chert, interbedded with thinner calcareous mudstone beds. Paine Member (middle part of formation):dark gray, thin-bedded, silty or fossiliferous limestone. Cottonwood Canyon Member (lower part of formation): black shale with basal conglomeratic lag deposit. Shallow marine. Thickness as much as 305 m (1000 ft). In Northwest Montana - Castle Reef Formation: Medium to light gray, thick-bedded limestone or dolomite. Sun River Member (upper part of formation): light gray dolomite with thick fossiliferous lenses. Shallow marine. Thickness as much as 300 m (984 ft). Allan Mountain Formation: Dark gray, thinly bedded limestone with thin mudstone and shale partings, and nodular chert. Shallow marine. Thickness as much as 200 m (656 ft).

Judith River Formation (Cretaceous) at surface, covers 5 % of this area

Light brown to light gray, fine- to coarse-grained sandstone with interbeds of gray to black carbonaceous shale, silty shale, and thin coal. Local Parkman Sandstone Member (lower part of formation):yellowish gray to brownish gray and olive green, fine- to medium-grained, cross-bedded sandstone interbedded with yellowish gray, silty shale. Estuarine, brackish, and nearshore marine. Thickness as much as 305 m (1000 ft).

Tullock Member of Fort Union Formation (Tertiary) at surface, covers 4 % of this area

Yellow sandstone interbedded with subordinate grayish brown and black shale and thin beds of coal. Alluvial plain. Thickness as much as 180 m (590 ft).

Lance Formation (Cretaceous) at surface, covers 4 % of this area

Orangish brown, coarse- to fine-grained sandstone with subordinate interbeds of shale and mudstone. Laterally equivalent to Hell Creek Formation. Fluvial. Thickness as much as 150 m (492 ft).

Lebo Member of Fort Union Formation (Tertiary) at surface, covers 4 % of this area

Dark gray carbonaceous shale, bentonitic claystone, sandstone, and coal. Alluvial plain. Thickness as much as 185 m (607 ft).

Thermopolis and Fall River Formations (Cretaceous) at surface, covers 4 % of this area

Thermopolis Formation (Kt): Dark gray to black shale with subordinate siltstone beds. Middle part of formation contains one or more thin sandstone beds with chert pebble horizons where Muddy Sandstone is not present. Offshore marine. Thickness as much as 305 m (1,000 ft). Fall River Formation (Kfr): Gray and brown, fine- to medium-grained, quartzose sandstone with thin interbeds of dark gray shale. Nearshore marine. Thickness as much as 70 m (1,214 ft).

Alluvium (Quaternary) at surface, covers 3 % of this area

Gravel, sand, silt, and clay deposits of stream and river channels, and floodplains.

Tensleep Formation (Pennsylvanian) at surface, covers 3 % of this area

Very light gray sandstone interbedded with subordinate carbonate, shale, and anhydrite. Cyclical marine, eolian, and sabkha. Thickness about 60 m (197 ft).

Bearpaw Formation (Cretaceous) at surface, covers 3 % of this area

Dark gray shale with several zones of calcareous concretions, a basal zone of ferruginous concretions, and numerous thin bentonite beds. Marine. Thickness as much as 300 m (984 ft).

Kootenai Formation (Cretaceous) at surface, covers 3 % of this area

Kootenai Formation (Kk, Kku, Kkm, Kkl): Red, maroon, and olive gray mudstone, tan or gray siltstone, calcareous concretions, limestone beds, and several prominent sandstone beds that include the Greybull Member (top of the formation in south-central Montana) and the Sunburst Member (middle to lower part of the formation in northwest-central Montana), both dominantly quartzose sandstone. Basal Cutbank or Pryor Conglomerate. Alluvial plain with local marine influence in the north. Thickness as much as 335 m (1,099 ft).

Chugwater Formation (Triassic) at surface, covers 3 % of this area

Red siltstone, sandstone, and shale with subordinate gypsum and local limestone bed at top. Shallow restricted marine and nonmarine. Thickness as much as 180 m (590 ft).

Amsden Formation (Pennsylvanian and Mississippian) at surface, covers 2 % of this area

Red shale, light gray limestone, and cherty and sandy limestone. Coastal plain or marine. Thickness as much as 180 m (590 ft).

Mowry Formation (Cretaceous) at surface, covers 2 % of this area

Light gray to silvery gray, platy to blocky, siliceous shale and subordinate thin-bedded, gray siltstone or very fine-grained sandstone laminae or beds. Fish scales common in central Montana. Ledge-forming, chert-bearing, fine- to medium-grained sandstone at top throughout west-central Montana. Marine. Thickness 240 m (787 ft).

Niobrara Formation (Cretaceous) at surface, covers 2 % of this area

Gray to dark gray shale with numerous thin bentonite beds. Chalky aggregates of coccoliths and rhabdoliths in upper part. MacGowan Concretionary Bed (middle part of formation): grayish brown concretionary dolostone and limestone with phosphatic pellets and gray to black chert pebbles. Marine. Lower part noncalcareous. Thickness as much as 9–23 m (30–75 ft).

Ellis Group: Swift, Rierdon, and Piper or Sawtooth Formations; not all formations present at all locations (Jurassic) at surface, covers 2 % of this area

Swift Formation (Jsw): Orangish brown, glauconitic, flaggy-bedded, commonly fossiliferous, fine-grained sandstone or sandy coquina with subordinate dark gray shale interbeds; chert pebbles common. In west-central and northwestern Montana, a dark gray, noncalcareous, micaceous shale forms the lower part of the formation, commonly with a basal chert-pebble conglomerate or conglomeratic sandstone as much as 3 m (10 ft) thick. Shallow marine. Thickness as much as 70 m (230 ft). Rierdon Formation (Jr): Gray, locally fossiliferous limestone that may contain floating grains of quartz sand, interbedded with greenish gray limy shale. Lagoonal and marine shelf. Thickness as much as 105 m (344 ft). Sawtooth Formation: Western Montana: dark gray, platy to shaly, dense limestone with local basal conglomerate. Central Montana: upper calcareous siltstone, middle dark gray shale with thin limestone interbeds, and lower fine-grained sandstone. Three local members Bowes, Firemoon, and Tampico, in descending order. Bowes Member: dark gray to medium gray, calcareous mudstone, limestone, and quartzose sandstone. Firemoon Member: dark to medium gray, limestone and calcareous mudstone. Tampico Member: very light gray, well-sorted quartz sandstone and siltstone, and chert-pebble conglomerate. Shallow marine. Thickness as much as 205 m (673 ft). Piper Formation (Jp): Upper part: red mudstone and gypsum; middle part: gray shale, limestone, and dolomite; lower part: red mudstone and gypsum. Marine and restricted coastal evaporite basins. Thickness as much as 75 m (246 ft).

Eagle Formation (Cretaceous) at surface, covers 1 % of this area

Gray or grayish brown, thick-bedded sandstone, sandy shale, and thin interbedded coal. Chert-pebble lag deposit common at top of formation. Virgelle Member (lower part of formation in parts of central Montana): very light gray, gray, or brown sandstone that coarsens upward. Root zone and thin carbonaceous beds at top of member. Delta, coastal plain, tidal flat, and marine shoreface and foreshore. Thickness as much as 150 m (492 ft).

Linley Member of Fort Union Formation (Tertiary) at surface, covers 1 % of this area

Reddish to grayish brown conglomerate interbedded with coarse-grained sandstone, siltstone, and mudstone. Alluvial fan deposits derived from Beartooth uplift. Thickness as much as 610 m (2,000 ft).

Claggett Formation (Cretaceous) at surface, covers 1 % of this area

Dark gray to gray shale that weathers brown, with thin, gray sandstone laminae and beds in upper or middle part and calcareous concretions in lower part. Marine. Thickness as much as 170 m (558 ft).

Hell Creek Formation (Cretaceous) at surface, covers 1 % of this area

Light gray, bentonitic claystone that alternates with gray to brown sandstone interbedded with carbonaceous shale. Laterally equivalent to Lance Formation. Fluvial and flood plain. Thickness as much as 335 m (1,100 ft).

Frontier Formation (Cretaceous) at surface, covers 0.9 % of this area

Western Montana: gray, fine- to medium-grained, locally conglomeratic sandstone with interbeds of dark gray carbonaceous shale. Local conglomerate, porcellanite, and coal. Central Montana: dark gray, carbonaceous shale interbedded with siltstone and sandstone, chert-pebble conglomerate, and coal. Big Elk Sandstone Member: light gray, chert-rich sandstone commonly stained dark red, interbedded with thin, dark gray to black, clayey shale. Boulder River Sandstone Member: gray to greenish gray, very fine-grained to conglomeratic, glauconitic sandstone. Brackish to nonmarine. Thickness exceeds 2,135 m (7,005 ft) in Lima Peaks region, and exceeds 915m in the Greenhorn, Snowcrest, Gravelly, and Pioneer Mountains of southwestern Montana. Elsewhere thickness as much as 215 m (705 ft).

Carlile Formation (Cretaceous) at surface, covers 0.9 % of this area

Dark to light gray, noncalcareous, partly silty or sandy shale with upper zone of white-weathering, calcareous concretions, middle zone of sandy, orange-weathering, calcareous concretions, and basal zone of ferruginous concretions. Marine. Thickness as much as 195 m (640 ft).

Morrison Formation (Jurassic) at surface, covers 0.8 % of this area

Green, gray, or red mudstone and marlstone with subordinate limestone and sandstone beds. Upper part Neocomian age in central Montana and contains carbonaceous black shale and coal. Fluvial, paludal, and lacustrine. Thickness as much as 180 m (590 ft).

Telegraph Creek Formation (Cretaceous) at surface, covers 0.8 % of this area

Thin interbeds of yellowish brown sandstone or siltstone and gray shale. Marine shoreface and offshore. Thickness as much as 200 m (656 ft).

Belle Fourche Formation (Cretaceous) at surface, covers 0.8 % of this area

Gray to black shale with ironstone concretions and numerous bentonite beds. Mosby Sandstone Member (upper part of formation in north- and east-central Montana): brown sandstone locally with chert pebbles, interbedded with gray shale. Big Elk Sandstone Member (lower part of formation in southwest-central Montana): light gray, chert-rich sandstone commonly stained dark red, interbedded with thin, dark gray to black clayey shale. Marine shelf. Thickness as much as 260 m (853 ft).

Glacial deposit (Quaternary) at surface, covers 0.7 % of this area

Dominantly till, outwash, and local glacial lake deposits. Shown only in western and south-central Montana. Laurentide glacial deposits are indicated with a map pattern.

Gravel (Quaternary and Tertiary) at surface, covers 0.6 % of this area

Variable deposits that range from pebble to boulder size and include sand, silt, and clay. Dominantly alluvial terrace, abandoned channel and floodplain, remnant alluvial fan, and local glacial outwash.

Pilgrim through Flathead Formation: Pilgrim, Park, Meagher, Wolsey, and Flathead Formations (Cambrian) at surface, covers 0.3 % of this area

Pilgrim Formation: Gray, commonly mottled limestone that may contain intraformational limestone conglomerate. Shallow marine. Thickness as much as 180 m (590 ft). Park Formation: Grayish green, fissile, micaceous shale with a few thin beds of calcareous sandstone and thin, gray limestone. Local arkose beds. Offshore marine. Thickness as much as 310 m (1,017 ft). Meagher Formation: Gray to bluish gray limestone and dolomitic limestone, locally mottled and with intraformational conglomerate beds. Shallow marine. Thickness as much as 300 m (984 ft). Wolsey Formation (CAw): Dark green and purplish gray fissile, micaceous shale, thin glauconitic limestone beds and thin, fine-grained sandstone beds. Shallow marine. Thickness as much as 145 m (476 ft). Flathead Formation (CAf): Pinkish gray to light gray sandstone or quartzite. Locally very glauconitic, pebbly, arkosic, or iron-stained. Marine shoreface. Thickness as much as 100 m (328 ft).

Intrusive rock (Tertiary or Cretaceous) at surface, covers 0.3 % of this area

Intrusive rock

Phosphoria Formation (Permian) at surface, covers 0.2 % of this area

Gray and tan dolomite, cherty limestone, bedded chert, siltstone, sandstone, and gray to black phosphatic and dolomitic shale. Marine shelf and offshore marine. Thickness as much as 255 m (837 ft).

Jefferson and Bighorn Formations: locally includes Beartooth Butte Formation in central Montana (Devonian and Ordovician) at surface, covers 0.2 % of this area

Jefferson Formation (Dj): Birdbear Member (upper part of formation): light to medium gray, sucrosic dolomite. Lower part of formation: grayish black, commonly petroliferous dolomite or limestone that may be interbedded with light gray quartzite. Marine. Thickness as much as 520 m (1,706 ft). Bighorn Formation (Ob): Yellowish gray to very pale orange crystalline dolomite with local basal sandstone. Marine shelf. Thickness as much as 120 m (394 ft). In central Montana - Beartooth Butte Formation: Light gray and grayish red dolomite and limestone breccia and conglomerate, sandy and silty dolomite, and dolomitic siltstone, sandstone, and shale. Isolated outcrops throughout central Montana. Estuarine. Thickness as much as 50 m (164 ft).

Three Forks through Bighorn Formation: Three Forks, Jefferson, and Bighorn Formations (Mississippian through Ordovician) at surface, covers 0.2 % of this area

Three Forks Formation (MDt): Sappington Member (upper part of formation): yellowish orange and yellowish gray siltstone. Trident Member (middle part of formation): greenish gray and light olive gray, fossiliferous, calcareous shale that contains interbeds and nodules of fossiliferous, argillaceous limestone. Logan Gulch Member (lower part of formation): yellowish gray and grayish red, argillaceous limestone breccia and shale breccia that may include dolomitic siltstone. Marine to restricted marine with evaporite basins. Thickness as much as 185 m (607 ft). Jefferson Formation (Dj): Birdbear Member (upper part of formation): light to medium gray, sucrosic dolomite. Lower part of formation: grayish black, commonly petroliferous dolomite or limestone that may be interbedded with light gray quartzite. Marine. Thickness as much as 520 m (1,706 ft). Bighorn Formation (Ob): Yellowish gray to very pale orange crystalline dolomite with local basal sandstone. Marine shelf. Thickness as much as 120 m (394 ft).

Metamorphic rock (Archean) at surface, covers 0.2 % of this area

Metamorphic rock

Phosphoria through Amsden Formation: Phosphoria, Quadrant, and Amsden Formations (Permian through Mississippian) at surface, covers 0.1 % of this area

Phosphoria Formation (Pp): Gray and tan dolomite, cherty limestone, bedded chert, siltstone, sandstone, and gray to black phosphatic and dolomitic shale. Marine shelf and offshore marine. Thickness as much as 255 m (837 ft). Quadrant Formation (PAq): Very light gray, yellowish or pinkish, well-sorted sandstone or quartzite, locally interbedded with subordinate limestone beds. Marine. Generally, thickness as much as 140 m (460 ft), but as much as 800 m (2,625 ft) in southwestern-most Montana. Amsden Formation (PAMa): Red shale, light gray limestone, and cherty and sandy limestone. Coastal plain or marine. Thickness as much as 180 m (590 ft).

Gneiss and amphibolite (Archean) at surface, covers < 0.1 % of this area

Gneiss and amphibolite

Piper Formation (Jurassic) at surface, covers < 0.1 % of this area

Upper part: red mudstone and gypsum; middle part: gray shale, limestone, and dolomite; lower part: red mudstone and gypsum. Marine and restricted coastal evaporite basins. Thickness as much as 75 m (246 ft).

Morrison through Chugwater Formation: Morrison, Swift, Rierdon, Piper, and Chugwater Formations (Jurassic and Triassic) at surface, covers < 0.1 % of this area

Morrison Formation (Jm): Green, gray, or red mudstone and marlstone with subordinate limestone and sandstone beds. Upper part Neocomian age in central Montana and contains carbonaceous black shale and coal. Fluvial, paludal, and lacustrine. Thickness as much as 180 m (590 ft). Swift Formation (Jsw): Orangish brown, glauconitic, flaggy-bedded, commonly fossiliferous, fine-grained sandstone or sandy coquina with subordinate dark gray shale interbeds; chert pebbles common. In west-central and northwestern Montana, a dark gray, noncalcareous, micaceous shale forms the lower part of the formation, commonly with a basal chert-pebble conglomerate or conglomeratic sandstone as much as 3 m (10 ft) thick. Shallow marine. Thickness as much as 70 m (230 ft). Rierdon Formation (Jr): Gray, locally fossiliferous limestone that may contain floating grains of quartz sand, interbedded with greenish gray limy shale. Lagoonal and marine shelf. Thickness as much as 105 m (344 ft). Piper Formation (Jp): Upper part: red mudstone and gypsum; middle part: gray shale, limestone, and dolomite; lower part: red mudstone and gypsum. Marine and restricted coastal evaporite basins. Thickness as much as 75 m (246 ft). Chugwater Formation (TRc): Red siltstone, sandstone, and shale with subordinate gypsum and local limestone bed at top. Shallow restricted marine and nonmarine. Thickness as much as 180 m (590 ft).

Intrusive rock (Late Proterozoic through Archean (age uncertain)) at surface, covers < 0.1 % of this area

Intrusive rock

Fort Union Formation (Paleocene) at surface, covers < 0.1 % of this area

(Northwest, Southwest, and Central Wyoming) - Brown to gray sandstone, gray to black shale, and thin coal beds. (East Wyoming) - Light-colored massive sandstone, drab shale, and thick coal beds.

Willwood Formation (Eocene) at surface, covers < 0.1 % of this area

Variegated claystone, shale, and sandstone; some lenticular gold-bearing quartzite conglomerate.

Oldest gneiss complex (Early Archean) at surface, covers < 0.1 % of this area

Chiefly layered granitic gneiss, locally migmatitic. Local masses of quartzite, metagraywacke, iron-formation, and other metasedimentary rocks and amphibolite and felsic gneiss thought to be volcanic; metasedimentary rocks in Beartooth Mountains contain detrital zircon dated at more than 3,400 Ma. Inclusions show evidence of granulite-facies metamorphism prior to 2,800 Ma. Mueller and others (1982) suggest that large areas in Beartooth Mountains were invaded by Late Archean granite (age about 2,800 Ma). Bighorn Mountains--Dates of metamorphism 3,000+ Ma.

Telegraph Creek and Niobrara Formations (Cretaceous) at surface, covers < 0.1 % of this area

Telegraph Creek (Ktc): Thin interbeds of yellowish brown sandstone or siltstone and gray shale. Marine shoreface and offshore. Thickness as much as 200 m (656 ft). Niobrara Formation (Kn): Gray to dark gray shale with numerous thin bentonite beds. Chalky aggregates of coccoliths and rhabdoliths in upper part. MacGowan Concretionary Bed (middle part of formation): grayish brown concretionary dolostone and limestone with phosphatic pellets and gray to black chert pebbles. Marine. Lower part noncalcareous. Thickness as much as 9–23 m (30–75 ft).

Greenhorn Formation (Cretaceous) at surface, covers < 0.1 % of this area

Gray to light gray calcareous shale and shaly marl with thin beds of limestone. Shale contains white to pink calcareous specks. Marine. Thickness as much as 100 m (30–75 ft).

Metabasite (Archean) at surface, covers < 0.1 % of this area

Metabasite

Rierdon Formation (Jurassic) at surface, covers < 0.1 % of this area

Gray, locally fossiliferous limestone that may contain floating grains of quartz sand, interbedded with greenish gray limy shale. Lagoonal and marine shelf. Thickness as much as 105 m (344 ft).

Alluvium and Colluvium (Pleistocene-Holocene) at surface, covers < 0.1 % of this area

Clay, silt, sand, and gravel in flood plains, fans, terraces, and slopes.

Thermopolis through Kootenai Formation: Thermopolis, Fall River, and Kootenai Formations (Cretaceous) at surface, covers < 0.1 % of this area

Thermopolis Formation (Kt): Dark gray to black shale with subordinate siltstone beds. Middle part of formation contains one or more thin sandstone beds with chert pebble horizons where Muddy Sandstone is not present. Offshore marine. Thickness as much as 305 m (1,000 ft). Fall River Formation (Kfr): Gray and brown, fine- to medium-grained, quartzose sandstone with thin interbeds of dark gray shale. Nearshore marine. Thickness as much as 70 m (1,214 ft). Kootenai Formation (Kk, Kku, Kkm, Kkl): Red, maroon, and olive gray mudstone, tan or gray siltstone, calcareous concretions, limestone beds, and several prominent sandstone beds that include the Greybull Member (top of the formation in south-central Montana) and the Sunburst Member (middle to lower part of the formation in northwest-central Montana), both dominantly quartzose sandstone. Basal Cutbank or Pryor Conglomerate. Alluvial plain with local marine influence in the north. Thickness as much as 335 m (1,099 ft).

Mesozoic and Paleozoic rocks (Upper Mississippian-Lower Cretaceous) at surface, covers < 0.1 % of this area

Mesozoic and Paleozoic rocks (North Wyoming). Shown in small areas of complex structure. East Flank of Absaroka Range - Dinwoody Formation, Phosphoria Formation and related rocks., Tensleep Sandstone, and Amsden Formation (Lower Triassic through Upper Mississippian). East flank of Bighorn Mountains - Cloverly, Morrison, Sundance, Gypsum Spring, Chugwater and Gypsum Spring Formations (Lower Cretaceous through Permian). Mesozoic and Paleozoic rocks (South Wyoming). Shown in small areas of complex structure. South side of Granite Mountains north of Green Mountain - Nugget Sandstone, Chugwater and Goose Egg Formations, Tensleep Sandstone, and Amsden Formation (Jurassic? through Upper Mississippian). South flank of Ferris Mountains--Nugget Sandstone and Chugwater and Goose Egg Formation (Jurassic? through Permian). Northeast flank of Seminoe Mountians--Cloverly, Morrison, Sundance, Chugwater, and Goose Egg Formations (Lower Cretaceous through Permain). West flank of Sierra Madre--Chugwater, Goose Egg, Casper, and Fountain Formations (Upper Triassic through Middle Pennsylvanian). East Flank of Laramie Mountains--Cloverly, Morrison, Sundance, Chugwater, and Goose Egg Formations, and, east of fault in T. 19 N., Casper Formation (Lower Creatceous through Middle Pennsylvanian). Nugget Sandstone (JTRn) (South) - Gray to dull-red, massive to coarsely crossbedded quartz sandstone.

Frontier Formation (Upper Cretaceous) at surface, covers < 0.1 % of this area

(Thrust Belt) - White to brown sandstone and dark-gray shale; oyster coquina in upper part; coal and lignite in lower part. (North and South Wyoming) - Gray sandstone and sandy shale.

Mowry and Thermopolis Shales (Lower Cretaceous) at surface, covers < 0.1 % of this area

Mowry Shale (Kmr) - Silvery-gray hard siliceous shale containing abundant fish scales and bentonite beds. Thermopolis Shale - Black soft fissile shale; Muddy Sandstone Member at top.

Three Forks, Jefferson, and Beartooth Formations and Bighorn Dolomite (Middle Ordovician-Upper Devonian) at surface, covers < 0.1 % of this area

Three Forks Formation (Northern Yellowstone area) - Pink, yellow, and green dolomitic siltstone and shale. Three Forks Formation (North Wyoming) - Yellow and greenish-gray shale and dolomitic siltstone. Jefferson Formation (Northern Yellowstone area) - Massive siliceous dolomite. Jefferson Formation (North Wyoming) - Fetid brown dolomite and limestone. Bighorn Dolomite (Northern Yellowstone area) - Light-gray massive siliceous dolomite. Bighorn Dolomite (North Wyoming) - Gray massive cliff-forming siliceous dolomite and locally dolomitic limestone. Beartooth Butte Formation - Red sandstone, limy siltstone, and limestone. Occurs only in the Beartooth Mountains.

Cloverly, Morrison, Sundance, and Gypsum Spring Formations (Middle Jurassic-Lower Cretaceous) at surface, covers < 0.1 % of this area

Cloverly Formation - Rusty sandstone at top, underlain by brightly variegated bentonitic claystone; chert-pebble conglomerate locally at base. Morrison Formation - Dully variegated claystone, nodular limestone, and gray silty sandstone. In southern Yellowstone and Jackson Hole areas the presence of Morrison is questionable. Sundance Formation (Js) - Greenish-gray glauconitic sandstone and shale, underlain by red and gray nonglauconitic sandstone and shale. Gypsum Spring Formation - Interbedded red shale, dolomite, and gypsum. In north Wyoming wedges out south in T. 39 N.

Tensleep Sandstone and Amsden Formation (Upper Mississippian-Permian) at surface, covers < 0.1 % of this area

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 Washakie Range, Owl Creek Mountains, and southern Bighorn Mountains. Amsden Formation (North Wyoming) - Red and green shale and dolomite; at base is brown sandstone. Tensleep Sandstone (Sorth Wyoming) - White to gray sandstone containing thin limestone and dolomite beds. Amsden Formation (South Wyoming) - Red and green shale and dolomite; at base is persistent red to brown sandstone.

Glacial deposits (Pleistocene-Holocene) at surface, covers < 0.1 % of this area

Till and outwash of sand, gravel, and boulders.