Silt, sand, sandstone, gravel and conglomerate. Predominantly interfingered fine- to coarse grained, poorly sorted, arkosic, fluvial deposits of light-gray, light-olive-gray, and grayish-green calcareous silt and sand, and locally poorly consolidated conglomerate, sandstone, and siltstone.
Upper part is white, light-gray, brownish-gray, yellow, redish-brown, and red sandstone and shale. Sandstone is very fine to coarse grained, friable, micaeous, crossbedded, and lenticular; locally contains gravel near base. contains numerous zones of ironstone and siltstone concretions of variable thickness. Middle part is light-gray, yellow, red brown and dark-gray, sandy carbonaceous shale; commonly contains a zone of concretions near top. Lower part is sandstone similar to that in upper except there are zones of siderite concretions and, locally a basal zone of chert pebbles. Approx. max thickness 600 ft.
Argillaceous chalk, limestone and shale. Chalk is medium gray to white, interbedded with thin layers of chalky shale; contains many fossil clams, oysters, and formanifera. Limestone is light gray to medium gray and yellowish gray, interbedded with medium-gray chalky shale; also contains fossil clams, oysters, and formanifera. Bedding plans commonly marked by thin layers of gypsum and locally a thin bed of red flint occurs at top of unit. Approx. max thickness 570 ft.
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.
Shale, limestone, and sandstone. At top, locally 5 feet of gray to pale-yellowish brown siltstone or very fine grained sandstone. Upper 200 feet of shale is drak gray to medium gray; locally contains ironstone concretions, and interbedded with thin siltstone. Lower 80 feet of shale is medium gray, calcareous, and contains many very thin bedded, fossiliferous, shaly limestone and calcareous shale layers. Approx. max thickness 300 ft.
Greenhorn Limestone- medium- to light-gray limestone interbedded with argillaceous limestone, marl and calcareous shale; contains Inoceramus fossils. Upper and lower contacts gradational. Approx. max thickness 30 ft. Graneros Shale- medium- to dark-gray, partly calcareous shale. Interbeds of siltstone, sandstone, and carbonaceous shale, and thin bentonite layers in upper part. Approx. max thickness 60 ft.
Shale and interbedded limestone. Shale is gray, green, red, reddish brown, or maroon, sandy, calcareous, fossiliferous, locally fissile; several fissile black shale beds are in lower 75 feet. Interbedded dark- to light-gray, medium- to thick-bedded, argillaceous, cherty limestone beds are very fossiliferous and locally contain shale partings. Approx. max thickness 300 ft
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.
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.
Shale, sandstone, and interbedded limestone. Shale is light gray to dark gray, greenish gray, red, or black; contains very thin layers of siltstone; locally very fossiliferous, carbonaceous. Sandstone is brownish gray to yellowish gray, or gray, argillaceous , and micaceous. Limestone is dark gray to medium gray, yellowish gray, thin bedded to thick bedded; very fossiliferous. Contains coal beds less than 1 ft. thick. Approx. max thickness 300 ft
Limestone and shale. Limestone is light gray to dark gray, yellowish gray to pale yellowish brown. Two limestones in the upper part are thin bedded to medium bedded, argillaceous, cherty and fossiliferous; two limestones in the lower part are medium to massive bedded, very cherty, and fossiliferous. Shale is gray, green, red, redish brown, calcareous, arenaceous, fossiliferous; locally fissile. Approx. max thickness 300 ft.
Shale and interbedded limestone. Shale is dark gray to light gray, brown, red, or green, sandy, calcareous, and fossiliferous. Interbedded dark- to light-gray, very thin to medium bedded, argillaceous, very fossiliferous limestone beds. Near top of unit a fine-grained, micaceous sandstone bed underlies a stromatolite limestone bed which has distinctive lobate bedding. Approx. max thickness 150 ft
Limestone, shale and siltstone. Limestone is dark gray to very light gray, yellowish gray, very thin bedded to massive bedded, and fossiliferous; locally the thin bedds are argillaceous other beds are oolitic and a few contain chert. Shale is medium gray, greenish gray, pale red, dark redish brown, black, sandy fossiliferous and calcareous; black shale in part is fissile. Siltstone is light gray to greenish yellow, massive, calcareous; locally sandy. Approx. max thickness 200 ft
Limestone and shale. Limestone is dark gray to light gray, brownish gray, very thin bedded to massive, argillaceous, fossiliferous; contains very thin layers of chert, pyrite crystals, and small flakes of mica near base. Shale is dark gray to light gray, greenish gray, red, and black; locally slighty sandy, calcareous, carbonaeous, fissile, and fossiliferous. Approx. max thickness 200 ft
Shale and limestone. Shale is dark gray to light gray, greenish gray, black, red, silty, sandy carbonaceous, fissile, calcareous; contains scattered limestone nodules. Limestone is medium gray to light gray, red, mottled thin bedded to thick bedded, sandy, shaly, vuggy, fossiliferous. Approx. max thickness 125 ft
Limestone and shale. Limestone is dark gray to light gray, very thin bedded to massive, sandy fossiliferous, and cherty. Shale is dark gray to light gray, maroon, black, fossiliferous, and calcareous. Approx. max thickness 75 ft
Shale and limestone. Shale is dark gray to medium gray, red , black, fossiliferous, calcareous and locally sandy. Limestone is dark gray to light gray, thin bedded to thick bedded, fossiliferous and locally sandy. Approx. max thickness 100 ft
Consists of fossiliferous, gray, ferruginous and yellowish fine-grained sandstone, arenaceous clays and a few interbeds of gray to brown sandy shale and coal totaling 172 ft thick at that section. Estimated thickness 500 ft.
Clay to boulder-size clasts with locally abundant organic material. Thickness up to 75 ft (23m).
Blue-gray to dark-gray, fissile to blocky shale with persistent beds of bentonite, black organic shale, or light-brown chalky shale. Contains minor sandstone, conglomerate, and abundant carbonate and ferruginous concretions. Thickness 1,000-2,700 ft (305-823 m).
Includes: Brule Formation (Oligocene)- White, pink, light-green, and light-brown, massive to thin-bedded, bentonitic claystone, tuffaceous siltstone, and well-bedded, calcareous, tuffaceous quartz sandstone. Thickness up to 150 ft (46 m). Chadron Formation (Eocene)- Upper beds are gray, light-brown to maroon bentonite, claystone, siltstone tuffaceous fine-grained sandstone, and local, silicified carbonate lenses. Basal portion consists of poorly cemented, white, coarse-grained arkose and conglomerate. Thickness up to 160 ft (49 m). Chamberlain Pass Formation (Eocene)- Pale olive to pale red, mottled mudstone containing white, cross-bedded channel sandstone with basal conglomerate. Thickness up to 32 ft (10 m). Slim Buttes Formation (Eocene)- White, grayish- to yellowish-orange,pale-red to pink siltstone, clayey siltstone, bentonitic claystone,medium- to fine-grained sandstone, and conglomerate. Thickness up to 48 ft (15 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 160-225 ft (49-69 m).
Clay to boulder-size clasts deposited as pediments, paleochannels, and terrace fills of former flood plains. Thickness up to 75 ft (23m).
Cyclic deposits with thin bedded limestones and interbedded red and green shales; Stranton Limestone at top, Vilsa Shale and Plattsburg Limestone at base.
Includes: Rosebud Formation (Miocene)- Pink siltstone with channel sandstone and concretions. Thickness up to 250 ft (76 m). Harrison Formation (Miocene)- Gray, silty sandstone and reworked volcanic ash with calcareous siltstone and marl. Thickness 180 ft (55 m). Turtle Butte Formation (Miocene)- Light-green to gray siltstone with sandstone channels containing claystone pebbles. Thickness 65 ft (20 m). Monroe Creek Formation (Oligocene)- Tan to grayish-tan, massive sandy siltstone and reworked volcanic ash. Thickness 100 ft (30 m). Sharps Formation (Oligocene)- Pink siltstone and claystone with concretionary layers, paleochannels, and beds of reworked volcanic ash. Thickness 360 ft (110 m).
Loose to well-cemented sand and gravel
Includes: Ash Hollow Formation- White, tan, and gray, well-cemented, calcareous sandstone and silty limestone often referred to as "mortar beds". Thickness 90-250 ft 27-76 m) Valentine Formation- Gray, unconsolidated, fine- to coarse grained, fluvial siltstone, channel sandstone, and gravel derived from western sources. Thickness 175-225 ft (53-69 m). Fort Randall Formation- Pink and gray claystone with interbedded sandstone. Also includes green to gray orthoquartzite, bentonitic clay, and conglomerate. Thickness up to 130 ft (40 m).
Cyclic deposits, principally shale with limestone, siltstone, minor sandstone units and thin coal seams.
Heterogeneous clay to gravel of glaciofluvial orgin. Thickness up to 60 ft (18m)
Cyclic deposits with shale, siltstone and minor thin limestone beds; Lawrence Formation at top and Stranger Formation at base.
UPPER MIOCENE ROCKS--Southwest Wyoming: South end of Wind River Range--Siliceous, arkosic, and locally radioactive sandstone, claystone, and conglomerate. Fission-track age about 27 Ma. Recent work suggests that part of these deposits may be of Eocene age. Pliocene and Miocene (as originally defined 2) South Pass Formation. Saratoga Valley--White to greenish-gray tuffaceous sandstone, siltstone, and claystone; locally conglomeratic. North Park Formation; Central Wyoming: Arkosic sandstone, conglomerate, and siltstone; some light-colored tuffaceous radioactive claystone and white cherty limestone. North of Sweetwater River in Granite Mountains--Light-colored tuffaceous radioactive claystone, siltstone, sandstone, and arkose. Moonstone Formation; East Wyoming: Light-colored tuffaceous claystone, sandstone, and conglomerate. Ogallala Formation in Denver Basin.
East: Ashy claystone and sandstone. Includes Castle Rock Conglomerate in region southeast of Denver. Northwest: Ashy claystone in North Park
Includes Piney Creek Alluvium and younger deposits
unconsolidated sand, silt, clay, and gravel
Heterogeneous, clay with silt to boulder-size clasts of glacial orgin. A geomorphic feature that is characterized by hummocky terrain with abundant sloughs resulting from stagnation of ice sheets. Composite thickness of all Upper Wisconsin till may be up to 300 ft (91 m).