Lower Miocene and Upper Oligocene rocks--Light-colored soft porous sandstone and underlying white tuffaceous claystone and siltstone. Arikaree Formation in Denver Basin; rocks equivalent to Upper and Lower Miocene rocks and White River Formation--Light-colored sandstone, white tuffaceous blocky claystone, and siltstone. Black Hills.
(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.
Soft gray sandstone, gray and brown carbonaceous shale, and thin coal beds.
Dark-gray concretionary marine shale; contains several bentonite beds.
White to pale-pink blocky tuffaceous claystone and lenticular arkosic conglomerate.
Light-colored sandstone and gray sandy shale containing marine fossils.
Clay, silt, sand, and gravel in flood plains, fans, terraces, and slopes.
Dark-gray sandy shale; Sage Breaks Member at top; Turner Sandy Member in middle.
Greenhorn Formation - Light-colored limestone, marl, and limy sandstone interbedded with gray concretionary shale. Belle Fourche Shale - Black soft bentonitic concretionary shale. Carlile Shale (Kcl) - Dark-gray sandy shale; Sage Breaks Member at top; Turner Sandy Member in middle.
Light-colored limestone and gray to yellow speckled limy shale.
Dark-gray clay shale and concretionary sandstone.
Red and white sandstone underlain by gray dolomite and limestone, red shale, and red and gray sandstone. Lowermost unit may be Late Mississippian in age.
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.
Greenhorn Formation - Light-colored limestone, marl, and limy sandstone interbedded with gray concretionary shale. Belle Fourche Shale - Black soft bentonitic concretionary shale. Mowry Shale (Kmr) - Silvery-gray hard siliceous shale containing abundant fish scales and bentonite beds.
Niobrara Formation (Kn) - Light-colored limestone and gray to yellow speckled limy shale. Carlile Shale (Kcl) - Dark-gray sandy shale; Sage Breaks Member at top; Turner Sandy Member in middle.
Blue-gray massive cherty limestone and dolomite. Locally includes unnamed dolomite and sandstone of Devonian and Cambrian(?) age.
Newcastle Sandstone - Gray sandstone and sandy shale containing some bentonite and coal. Skull Creek Shale - Black soft fissile shale.
Amphibolite, hornblende gneiss, biotite gneiss, quartzite, iron-formation, metaconglomerate, marble, and pelitic schist; locally preserved textures and structures suggest origin to be sedimentary or volcanic. Older than 2,875 Ma in Teton Range; older than 3,200 Ma in Granite Mountains; older than 2,600 Ma in Medicine Bow Mountains and Sierra Madre, where it is the Late Archean Phantom Lake Metamorphic Suite 3.
Mostly locally derived clasts. Includes some glacial deposits along east flank of Wind River Range. Locally includes some Tertiary gravels.
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.
Greenish-gray glauconitic sandstone and shale, underlain by red and gray nonglauconitic sandstone and shale.
Dark-gray to black, silty to sandy shale with several zones of septarian, fossiliferous, carbonate concretions. Contains up to three sandstone units in the upper portion of the formation and sandy calcareous marl at the base. Thickness up to 330 ft (100 m).
Consists mainly of gray, fine, loose to compact sand that has layers of hard, fine-grained dark-gray concretions which vary from few in to 15 in and often have tabular form. Includes a large amount of volcanic ash mixed in with the sand. Contains a number of channels filled with coarse conglomerate along ridge south of North Platte River. About 500 ft thick.
Medicine Bow Mountains--Gaps Intrusion 3 (granitic). Hartville uplift--Granite and quartz monzonite of Flattop Butte 6; age 2,150+/- Ma.
Red sandstone and siltstone, white gypsum, halite, and purple to white dolomite and limestone.
Blue-gray to dark-gray, fissile to blocky shale with persistent beds of bentonite, black organic shale, and light-brown chalky shale. Contains minor sandstone, conglomerate, and abundant carbonate and ferruginous concretions. Thickness up to 1,000 ft (305 m).
Dark-gray to black bentonitic shale containing minor limestone lenses, bentonite layers, fossiliferous calcarenite, and large, ferruginous, carbonate concretions. Thickness 150-350 ft (46-107 m).
White to dark-gray argillaceous chalk, marl, and shale. Weathers yellow to orange. Contains thin, laterally continuous bentonite beds, chalky carbonaceous shale, minor sand, and small concretions. Thickness up to 150 ft (46 m).
Silvery-gray hard siliceous shale containing abundant fish scales and bentonite beds.
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.
Mostly medium to dark-gray, brownish-gray, and black, fissle clay shale. Locally grades to thin beds of calcareous, silty shale or claystone, marl, shaly sandstone, and sandy shale. Locally contains thin seams of gypsum and sparse selenite crystals. Approx. max thickness 1970 ft.
Granitic rocks of 1,700-Ma Group
Clay, some claystone, silt and siltstone. Predominantly greenish gray and volcaniclastic. Other occurrences are greenish gray to white and bentonitic. Local channel sandstone at base. Aprox thickness 195 ft.
Clay to boulder-size clasts with locally abundant organic material. Thickness up to 75 ft (23m).
Gray shale, mudstone, marl, calcarenite, and shaly limestone grading upward into light-gray to tan, alternating marl and thin-bedded, fossiliferous limestone. Thickness up to 40 ft (12 m).
(loess and sand dune) Silt to medium-grained sand. Deposited as sand sheets and barchan, linear, and dome-like dunes and as veneer on uplands. Thickness up to 300 ft (91m).
Clay to boulder-size clasts deposited as pediments, paleochannels, and terrace fills of former flood plains. Thickness up to 75 ft (23m).