Geologic units in Park county, Wyoming

Additional scientific data in this geographic area

Absaroka Volcanic Supergroup: Sunlight Group - Wapiti Formation (Eocene) at surface, covers 12 % of this area

Andesitic volcaniclastic rocks.

Absaroka Volcanic Supergroup: Thorofare Creek Group - Wiggins Formation (Eocene) at surface, covers 10 % of this area

Light-gray volcanic conglomerate and white tuff, containing clasts of igneous rocks.

Willwood Formation (Eocene) at surface, covers 10 % of this area

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

Undivided surficial deposits (Pleistocene-Holocene) at surface, covers 8 % of this area

Mostly alluvium, colluvium, and glacial and landslide deposits. Primarily in Yellowstone area and Bighorn Mountains.

Absaroka Volcanic Supergroup: Thorofare Creek Group - Two Ocean and Langford Formations (Eocene) at surface, covers 7 % of this area

Dark-colored andesitic volcaniclastic rocks and flows underlain by light-colored andesitic tuffs and flows. In places may include Trout Peak Trachyandesite of Sunlight Group.

Rhyolite flows, tuff, and intrusive igneous rocks (Pleistocene) at surface, covers 6 % of this area

Includes Plateau Rhyolite (age about 0.07 Ma) and interlayered sediments, Mount Jackson Rhyolite (age 0.6 to about 1 Ma), Lewis Canyon Rhyolite (age about 0.9 Ma); and Lava Creek Tuff of Yellowstone Group (age 0.6 to about 1 Ma).

Gravel, pediment, and fan deposits (Pleistocene-Holocene) at surface, covers 5 % of this area

Mostly locally derived clasts. Includes some glacial deposits along east flank of Wind River Range. Locally includes some Tertiary gravels.

Cody Shale (Late Cretaceous) at surface, covers 4 % of this area

(Northern Yellowstone area) - Gray to brown shale and siltstone. (North and South Wyoming) - Dull-gray shale, gray siltstone, and fine-grained gray sandstone.

Alluvium and Colluvium (Pleistocene-Holocene) at surface, covers 4 % of this area

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

Fort Union Formation (Paleocene) at surface, covers 4 % 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.

Absaroka Volcanic Supergroup: Washburn Group (Eocene) at surface, covers 4 % of this area

Includes Sepulcher Formation (andesitic and dacitic volcaniclastic rocks), Lamar River Formation (andesitic lava and volcaniclastic rocks), and Cathedral Cliffs Formation (light-colored andesitic volcaniclastic rocks).

Oldest gneiss complex (Early Archean) at surface, covers 3 % 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.

Landslide deposits (Pleistocene-Holocene) at surface, covers 3 % of this area

Locally includes intermixed landslide and glacial deposits, talus, and rock-glacier deposits.

Glacial deposits (Pleistocene-Holocene) at surface, covers 3 % of this area

Till and outwash of sand, gravel, and boulders.

Absaroka Volcanic Supergroup: Sunlight Group - Trout Peak Trachyandesite (Eocene) at surface, covers 3 % of this area

Trout Peak Trachyandesite.

Mesaverde Formation or Mesaverde Group (Upper Cretaceous) at surface, covers 2 % of this area

Mesaverde Formation (north Wyoming) - Light-colored massive to thin-bedded sandstone, gray sandy shale, and coal beds. In Jackson Hole locally contains gold-bearing quartzite conglomerate. North of North Fork Powder River east of the Bighorn Mountains, consists solely of the Parkman Sandstone Member. Mesaverde Group (South Wyoming) - Includes Almond Formation, Ericson Sandstone, Rock Springs and Blair Formations in Rock Springs uplift; Almond Formation (white and brown soft sandstone, gray sandy shale, coal and carbonaceous shale), Pine Ridge Sandstone (light-gray sandstone and thin coal beds), and Allen Ridge (gray sandstone, shale, and thin coal beds) and Haystack Mountains (gray marine sandstone and shale) Formations in Rawlins uplift; Pine Ridge Sandstone (light-gray sandstone and thin coal beds) and Rock River Formation (soft sandstone and sandy shale) in Laramie Basin.

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

Chalky-white to gray sandstone, yellow, green, and dark-gray bentonitic claystone, white tuff, and thin coal beds.

Absaroka Volcanic Supergroup: Thorofare Creek Group - Aycross Formation (Eocene) at surface, covers 1 % of this area

Brightly variegated bentonitic claystone and tuffaceous sandstone, grading laterally into greenish-gray sandstone and claystone. In and east of Jackson Hole contains gold-bearing lenticular quartzite conglomerate.

Lance Formation (Upper Cretaceous) at surface, covers 1.0 % of this area

(North Wyoming) - Thick-bedded buff sandstone and drab to green shale; thin conglomerate lenses. (South and Northeast Wyoming) - Brown and gray sandstone and shale; thin coal and carbonaceous shale beds.

Frontier Formation (Upper Cretaceous) at surface, covers 0.8 % 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.

Absaroka Volcanic Supergroup: Thorofare Creek and Sunlight Groups (Eocene) at surface, covers 0.8 % of this area

Thorofare Creek Group - Light-colored volcaniclastic strata, andesite lava flows, and dark-brown breccia; Sunlight Group - including Trout Peak Trachyandesite, Wapiti Formation (andesitic volcaniclastic rocks), Crescent Hill Basalt, and Mount Wallace Formation (felsic and mafic volcaniclastic rocks).

Madison Limestone, Darby or Three Forks, Jefferson, and Beartooth Butte Formations, and Bighorn Dolomite (Middle Ordovician-Upper Mississippian) at surface, covers 0.7 % of this area

Madison Limestone or Group - Group includes Mission Canyon Limestone (blue-gray massive limestone and dolomite), underlain by Lodgepole Limestone (gray cherty limestone and dolomite). Darby Formation - Yellow and greenish-gray shale and dolomitic siltstone underlain by fetid brown dolomite and limestone. Three Forks Formation - Yellow and greenish-gray shale and dolomitic siltstone. Jefferson Formation - Fetid brown dolomite and limestone. Beartooth Butte Formation - Red sandstone, limy siltstone, and limestone. Occurs only in the Beartooth Mountains.

Intrusive igneous rocks (Eocene) at surface, covers 0.7 % of this area

Felsic and mafic igneous bodies; the larger are mainly felsic.

Gallatin Limestone, Gros Ventre Formation and equivalents, Flathead Sandstone, and Cambrian Rocks (Middle Cambrian-Upper Cambrian) at surface, covers 0.7 % of this area

Gallatin Limestone (North Wyoming) - Blue-gray and yellow mottled hard dense limestone. Gros Ventre Formation (North Wyoming) - Soft green micaceous shale (Upper and Middle Cambrian Park Shale Member), underlain by blue-gray and yellow mottled hard dense limestone (Middle Cambrian Death Canyon Limestone Member), and soft green micaceous shale (Middle Cambrian Wolsey Shale Member). Flathead Sandstone (North Wyoming) - Dull-red quartzitic sandstone. Cambrian Rocks (South Wyoming) - South flank of Granite Mountains--Blue-gray and yellow mottled hard dense limestone interbedded with soft green micaceous shale; dull-red quartzitic sandstone at base. On and south of Rawlins uplift--Glauconitic quartzitic sandstone.

Mesozoic and Paleozoic rocks (Upper Mississippian-Lower Cretaceous) at surface, covers 0.7 % 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.

Absaroka Volcanic Supergroup: Sunlight Group (Eocene) at surface, covers 0.5 % of this area

Including Trout Peak Trachyandesite, Wapiti Formation (andesitic volcaniclastic rocks), Crescent Hill Basalt, and Mount Wallace Formation (felsic and mafic volcaniclastic rocks).

Huckleberry Ridge Tuff of Yellowstone Group (Pliocene) at surface, covers 0.5 % of this area

Lavender to gray-brown welded rhyolite tuff.

Basalt flows and intrusive igneous rocks (Pleistocene) at surface, covers 0.5 % of this area

Yellowstone area--Includes Osprey, Madison River, Swan Lake Flat, and Falls River Basalts, basalts of Mariposa Lake, Undine Falls Basalt, and gravels, sands, silts, and basalts of The Narrows. In and adjacent to Absaroka and Washakie Ranges--Includes basalt of Lava Mountain (age about 0.5 Ma).

Frontier Formation and Mowry and Thermopolis Shales (Lower Cretaceous-Upper Cretaceous) at surface, covers 0.5 % of this area

Frontier Formation (Kf) - Gray sandstone and sandy shale. In Northern Yellowstone area, Yellowish- to medium-gray sandstone; tuffaceous and carbonaceous in lower part. 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.

Tatman Formatin (Eocene) at surface, covers 0.5 % of this area

Drab nontuffaceous claystone, oil shale, lignite, and sandstone.

Cloverly and Morrison Formations or Inyan Kara Group (Upper Jurassic-Lower Cretaceous) at surface, covers 0.4 % of this area

Cloverly Formation (North and South Wyoming) - Rusty sandstone at top, underlain by brightly variegated bentonitic claystone; chert-pebble conglomerate locally at base. Cloverly Formation (Northeast Wyoming - Hartville Uplift) - Rusty to light-gray sandstone containing lenticular chert-pebble conglomerate interbedded with variegated bentonitic claystone. Morrison Formation (North and South Wyoming) - Dully variegated claystone, nodular limestone, and gray silty sandstone. In southern Yellowstone and Jackson Hole areas the presence of Morrison is questionable. Morrison Formation (Northeast Wyoming) - dully variegated siliceous claystone, nodular white limestone, and gray silty sandstone. Inyan Kara Group (Northeast - Black Hills) - Rusty to light-gray sandstone containing lenticular chert-pebble conglomerate interbedded with variegated bentonitic claystone. Includes Fall River and Lakota Formations.

Mowry and Thermopolis Shales (Lower Cretaceous) at surface, covers 0.4 % 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.

Chugwater and Dinwoody Formations (Lower Triassic-Upper Triassic) at surface, covers 0.3 % of this area

Chugwater Formation - Red siltstone and shale. Alcova Limestone Member in upper middle part. Thin gypsum partings near base. Dinwoody Formation - Olive-drab hard dolomitic thin-bedded siltstone.

Madison Limestone or Group (Lower Mississippian-Upper Mississippian) at surface, covers 0.3 % of this area

Group includes Mission Canyon Limestone (blue-gray massive limestone and dolomite), underlain by Lodgepole Limestone (gray cherty limestone and dolomite).

Granite gneiss (Late Archean) at surface, covers 0.3 % of this area

Layered to massive, locally migmatitic; metasedimentary and metavolcanic rocks locally common. Includes Webb Canyon Gneiss in Teton Range.

Sundance and Gypsum Spring Formations (Middle Jurassic-Upper Jurassic) at surface, covers 0.2 % of this area

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.

Cloverly, Morrison, Sundance, and Gypsum Spring Formations (Middle Jurassic-Lower Cretaceous) at surface, covers 0.2 % 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.

Madison Group, Darby Formation, Three Forks and Jefferson Formations (Upper Devonian-Upper Mississippian) at surface, covers 0.2 % of this area

Madison Limestone or Group (Thrust Belt, North Wyoming and Northern Yellowstone area) - Group includes Mission Canyon Limestone (blue-gray massive limestone and dolomite), underlain by Lodgepole Limestone (gray cherty limestone and dolomite). Darby Formation (Thrust Belt and North Wyoming) - Yellow and greenish-gray shale and dolomitic siltstone underlain by fetid brown dolomite and limestone. Three Forks Formation (Northern Yellowstone area) - Pink, yellow, and green dolomitic siltstone and shale. Jefferson Formation (Northern Yellowstone area) - Massive siliceous dolomite.

Absaroka Volcanic Supergroup: Thorofare Creek Group - Tepee Trail Formation (Eocene) at surface, covers 0.2 % of this area

Green and olive-drab hard generally well bedded andesitic conglomerate, sandstone, and claystone.

Three Forks, Jefferson, and Beartooth Formations and Bighorn Dolomite (Middle Ordovician-Upper Devonian) at surface, covers 0.2 % 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.

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.

Phosphoria Formation and Related Rocks, Wells Formation, Amsden Formations, Quadrant Sandstone, and Tensleep Sandstone (Upper Mississippian-Permian) at surface, covers 0.1 % of this area

Phosphoria Formation and Related Rocks (Thrust Belt) - Upper part is dark- to light-gray chert and shale with black shale and phosphorite at top; lower part is black shale, phosphorite, and cherty dolomite. Phosphoria Formation and Related Rocks (Northern Yellowstone area) - Brown sandstone and dolomite, cherty phosphatic and glauconitic dolomite, phosphatic sandstone and dolomite, and greenish-gray to black shale. Intertonguing equivalent is Shedhorn Sandstone. Phosphoria Formation and Related Rocks (North Wyoming) - Brown sandstone and dolomite, cherty phosphatic and glauconitic dolomite, phosphatic sandstone and dolomite, and greenish-gray to black shale. Intertonguing equivalents of parts of Phosphoria are Park City Formation (primarlily cherty dolomite, limestone, and phosphatic gray shale) and Shedhorn Sandstone. Wells Formation - Gray limestone interbedded with yellow limy sandstone. Amsden Formation (Thrust Belt) - Red and gray cherty limestone and shale, sandstone, and conglomerate. Amsden Formation (Northern Yellowstone area) - Red and green dolomitic shale, siltstone, and sandstone. Amsden Formation (North Wyoming) - Red and green shale and dolomite; at base is brown sandstone. Quadrant Sandstone - Light-gray sandstone. Tensleep Sandstone - 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.

Bighorn Dolomite, Gallatin Group, Gros Ventre Formation, Snowy Range Formation, Pilgrim Limestone, Park Shale, Meagher Limestone, Wolsey Shale, Flathead Sandstone, Whitewood Dolomite, and Winnipeg and Deadwood Formations (Middle Cambrian-Upper Ordovician) at surface, covers 0.1 % of this area

Bighorn Dolomite (Thrust Belt and North Wyoming) - Gray massive cliff-forming siliceous dolomite and locally dolomitic limestone. Bighorn Dolomite (Northern Yellowstone area) - Light-gray massive siliceous dolomite. Gallatin Limestone or Group (Thrust Belt) - Gray and tan limestone. Gallatin Limestone or Group (North Wyoming) - Blue-gray and yellow mottled hard dense limestone. Gallatin Group-Snowy Range Formation (Northern Yellowstone area) - Medium-gray limestone and underlying greenish-gray shale. Gallatin Group-Pilgrim Limestone (Northern Yellowstone area) - Blue-gray and yellow mottled hard limestone. Gros Ventre Formation (Thrust Belt) - Greenish-gray micaceous shale. Gros Ventre Formation (North Wyoming) - Soft green micaceous shale (Upper and Middle Cambrian Park Shale Member), underlain by blue-gray and yellow mottled hard dense limestone (Middle Cambrian Death Canyon Limestone Member), and soft green micaceous shale (Middle Cambrian Wolsey Shale Member). Park Shale (Northern Yellowstone area) - Green micaceous soft shale. Upper part may be Late Cambrian. Meagher Limestone (Northern Yellowstone area) - Blue-gray and yellow mottled hard limestone. Wolsey Shale (Northern Yellowstone area) - Green micaceous soft shale. Flathead Sandstone (Northern Yellowstone area and North Wyoming) - Dull-red quartzitic sandstone. Whitewood Dolomite (Northeast Wyoming) - Buff massive fossiliferous dolomite. Winnipeg Formation (Northeast Wyoming) - Pink to yellow siltstone and shale. Deadwood Formation (Northeast Wyoming) - Red and brown quartzitic sandstone.

Kootenai and Morrison Formations and Ellis Group (Middle Jurassic-Lower Cretaceous) at surface, covers < 0.1 % of this area

Kootenai Formation - Rusty thin-bedded sandstone, grayish-red soft claystone, white limestone, and chert-pebble conglomerate. Morrison Formation (Northern Yellowstone area) - Variegated silty claystone and fine-grained sandstone. Ellis Group - includes Swift, Rierdon, and Sawtooth Formations. Swift Formation - Calcareous glauconitic sandstone and sandy limestone. Rierdon Formation - Mudstone, siltstone, shale, and basal limestone. Sawtooth Formation - Red beds and limestone.

Everts Formation, Eagle Sandstone, and Telegraph Creek Formation (Upper Cretaceous) at surface, covers < 0.1 % of this area

Massive to thin-bedded sandstone, mudstone, and shale.

Chugwater Formation or Group (Lower Triassic-Upper Triassic) at surface, covers < 0.1 % of this area

Chugwater Formation (North and Northeast Wyoming) - Red siltstone and shale. Alcova Limestone Member in upper middle part in north Wyoming. Thin gypsum partings near base in north and northeast Wyoming. Chugwater Group or Formation (South Wyomingt) - Red shale and siltstone containing thin gypsum partings near base. Group includes Popo Agie Formation (red shale and red, yellow, and purple siltstone; lenses of lime-pellet conglomerate), Crow Mountain Sandstone (red and gray, thick bedded), Alcova Limestone, and Red Peak Formation (red siltstone and shale). Chugwater Formation includes as members all the units listed above. Includes overlying Jelm Formation in Shirley and Seminoe Mountains and at northern end of Laramie Basin. Jelm Formation - Red sandstone.

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

Greenish-gray bentonitic tuffaceous sandstone and conglomerate.

Bighorn Dolomite (Middle Ordovician-Upper Ordovician) at surface, covers < 0.1 % of this area

Light-gray massive siliceous dolomite in northern Yellowstone area. Gray massive cliff-forming siliceous dolomite and locally dolomitic limestone in Thrust belt and northern Wyoming.

Intrusive igneous rocks (Cretaceous?) at surface, covers < 0.1 % of this area

Gray to buff monzonite porphyry. Beartooth Mountains.

Lance Formation, Fox Hills Sandstone, Meeteetse Formation, and Bearpaw and Lewis Shales (Upper Cretaceous) at surface, covers < 0.1 % of this area

In the Bighorn Basin consists of Lance, Meeteetse and, in the southeastern part, tongue of Lewis Shale; in the northern part of the Wind River Basin, of Lance, Meeteetse, and Lewis, and, in the southeastern part of the basin, of Lance and Lewis; on the west side of the Powder River Basin north of T. 45 N., of Lance, Fox Hills, and Bearpaw, and, to the south, of Lance, Fox Hills, and Lewis. Lance Formation - Thick-bedded buff sandstone and drab to green shale; thin conglomerate lenses. Fox Hills Sandstone - Light-colored sandstone and gray sandy shale containing marine fossils. Meeteetse Formation - Chalky-white to gray sandstone, yellow, green, and dark-gray bentonitic claystone, white tuff, and thin coal beds. Bearpaw Shale - Dark-greenish-gray shale containing thin gray sandstone partings. Lewis Shale - Gray marine shale containing many gray and brown lenticular concretion-rich sandstone beds.

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

Quartzofeldspathic gneiss

Quartz monzonite of North Yellowstone (Late Archean) at surface, covers < 0.1 % of this area

Quartz monzonite of North Yellowstone

Intrusive and extrusive igneous rocks (Miocene-Pliocene) at surface, covers < 0.1 % of this area

Composition ranges from hornblende monzonite to basalt. In Yellowstone area includes andesite and basalt of Emerald Lake (age about 2 Ma), rhyolite of Broad Creek, Pliocene Junction Butte Basalt, and gravel of Mount Everts. Age of basalt on Crescent Mountain 3.6 Ma.

Tongue River Member of Fort Union Formation (Tertiary) at surface, covers < 0.1 % of this area

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

Crandall Conglomerate (Eocene) at surface, covers < 0.1 % of this area

Nonvolcanic conglomerate containing clasts of Lower Paleozoic rocks.

Tullock Member of Fort Union Formation (Tertiary) at surface, covers < 0.1 % 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 < 0.1 % 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).

Bearpaw Formation (Cretaceous) at surface, covers < 0.1 % 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).

Cloverly, Morrison, and Sundance 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.

Gravel (Quaternary) at surface, covers < 0.1 % 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.

Niobrara Formation (Cretaceous) at surface, covers < 0.1 % 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).

Granitic rocks of 2,600-Ma Age Group (Late Archean) at surface, covers < 0.1 % of this area

Teton Range--Mount Owen Quartz Monzonite. Age 2,500+/- Ma; may be of Early Proterozoic age. Gros Ventre and Washakie Ranges--Granitic rocks. Yellowstone National Park, Owl Creek, Granite, and Seminoe Mountains, Rawlins uplift, and Medicine Bow Mountains--Granite. Wind River Range--Granodiorite to porphyritic and equigranular granite. Sierra Madre--Granite and granodiorite. Laramie Mountains--Granite, amphibolite, and minor amounts of metasedimentary rocks. Hartville uplift--Granite and quartz monzonite. Black Hills uplift--Granite and minor amounts of metasedimentary rocks.

Judith River Formation (Cretaceous) at surface, covers < 0.1 % 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).

Absaroka Volcanics Supergroup (Tertiary) at surface, covers < 0.1 % of this area

Calc-alkalic andesite and dacite extrusive rock with lesser amounts of potassic, alkalic, and mafic lava; minor amounts of rhyodacitic ash-flow tuff associated with mafic lava; and dark gray, very fine-grained basalt or andesite intrusive breccia.

Chugwater and Goose Egg Formations (Permian-Upper Triassic) at surface, covers < 0.1 % of this area

Chugwater Formation (North Wyoming) - Red siltstone and shale. Alcova Limestone Member in upper middle part in north Wyoming. Thin gypsum partings near base in north and northeast Wyoming. Goose Egg Formation - Red sandstone and siltstone, white gypsum, halite, and purple to white dolomite and limestone. Chugwater Group or Formation (South Wyoming) - Red shale and siltstone containing thin gypsum partings near base. Group includes Popo Agie Formation (red shale and red, yellow, and purple siltstone; lenses of lime-pellet conglomerate), Crow Mountain Sandstone (red and gray, thick bedded), Alcova Limestone, and Red Peak Formation (red siltstone and shale). Chugwater Formation includes as members all the units listed above. Includes overlying Jelm Formation in Shirley and Seminoe Mountains and at northern end of Laramie Basin. Jelm Formation - Red sandstone.

Alluvium (Quaternary) at surface, covers < 0.1 % of this area

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

Telegraph Creek Formation (Cretaceous) at surface, covers < 0.1 % 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).

Schist and gneiss (Archean) at surface, covers < 0.1 % of this area

Schist and gneiss

Eagle Formation (Cretaceous) at surface, covers < 0.1 % 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).

Lebo Member of Fort Union Formation (Tertiary) at surface, covers < 0.1 % of this area

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

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

Dark gray, conglomeratic, feldspathic, lenticular sandstone interbedded with varicolored dark mudstone, claystone, bentonite, and coal. Fluvial. Thickness as much as 610 m (2,000 ft).

Claggett Formation (Cretaceous) at surface, covers < 0.1 % 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).

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

Light-colored, fine- to medium-grained, lenticular sandstone and medium to light gray or locally greenish, yellowish, or brownish gray mudstone. Shallow marine and brackish. Thickness as much as 425 m (1,395 ft).

Madison Group: Mission Canyon and Lodgepole Formations; or Castle Reef and Allan Mountain Formations (Mississippian) at surface, covers < 0.1 % 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).

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

Eagle Formation (Ke): 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). Telegraph Creek Formation (Ktc): Thin interbeds of yellowish brown sandstone or siltstone and gray shale. Marine shoreface and offshore. Thickness as much as 200 m (656 ft).

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

Gneiss and amphibolite