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Mineral Resources > Online Spatial Data > Geology > by state > Wyoming Geology

Geologic units in Platte county, Wyoming

[Additional scientific data in this geographic area]

Gravel, pediment, and fan deposits (Phanerozoic | Cenozoic | Quaternary | Pleistocene Holocene) at surface, covers 4 % of this area

GRAVEL, PEDIMENT, AND FAN DEPOSITS--Mostly locally derived clasts. Includes some glacial deposits along east flank of Wind River Range. Locally includes some Tertiary gravels.

Lithology: unconsolidated deposit

Peridotite intrusive rocks (Archean) at surface, covers < 0.1 % of this area

PERIDOTITE INTRUSIVE ROCKS--In Laramie Mountains.

Lithology: peridotite

White River Formation--Chadron Member (Phanerozoic | Cenozoic | Tertiary | Oligocene ) at surface, covers 0.4 % of this area

WHITE RIVER FORMATION Chadron Member--Light-gray to dark-red tuffaceous claystone, sandstone, and lenticular conglomerate.

Lithology: fine-grained mixed clastic; medium-grained mixed clastic; mixed clastic/volcanic

Sundance Formation (Phanerozoic | Mesozoic | Jurassic-Middle Jurassic-Late) at surface, covers < 0.1 % of this area

SUNDANCE FORMATION--Greenish-gray glauconitic sandstone and shale, underlain by red and gray nonglauconitic sandstone and shale.

Lithology: sandstone; shale

Dune sand and loess (Phanerozoic | Cenozoic | Quaternary | Pleistocene Holocene) at surface, covers 11 % of this area

DUNE SAND AND LOESS--Includes active and dormant sand dunes. In northwestern Wyoming is chiefly loess (age 12,000-19,000 years).

Lithology: dune sand; loess

Metasedimentary and metavolcanic rocks (Archean) at surface, covers 0.7 % of this area

METASEDIMENTARY AND METAVOLCANIC ROCKS--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.

Lithology: metasedimentary rock; metavolcanic rock

Goose Egg Formation (Phanerozoic | Paleozoic Mesozoic | Permian Triassic-Early) at surface, covers 0.2 % of this area

GOOSE EGG FORMATION--Red sandstone and siltstone, white gypsum, halite, and purple to white dolomite and limestone.

Lithology: mudstone; carbonate; evaporite; dolostone (dolomite)

Alluvium and Colluvium (Phanerozoic | Cenozoic | Quaternary | Pleistocene Holocene) at surface, covers 7 % of this area

ALLUVIUM AND COLLUVIUM--Clay, silt, sand, and gravel in flood plains, fans, terraces, and slopes.

Lithology: alluvium; colluvium

Chugwater Formation (N, NE), or Chugwater Formation or Group (S) (Phanerozoic | Mesozoic | Triassic-Early Triassic-Middle(?) Triassic-Late) at surface, covers 0.1 % of this area

CHUGWATER FORMATION (north, 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. [None mapped in the NE]; CHUGWATER FORMATION OR GROUP (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.

Lithology: siltstone; shale; sandstone; limestone; conglomerate

White River Formation--Brule Member (Phanerozoic | Cenozoic | Tertiary | Oligocene ) at surface, covers 1 % of this area

WHITE RIVER FORMATION Brule Member--Pale-pink to white blocky tuffaceous claystone and lenticular sandstone. Locally includes the Upper Conglomerate Member (Twru).

Lithology: fine-grained mixed clastic; medium-grained mixed clastic; mixed clastic/volcanic

Chugwater and Goose Egg Formations (Phanerozoic | Paleozoic Mesozoic | Permian Triassic-Early(?) Triassic-Middle(?) Triassic-Late) at surface, covers 0.8 % of this area

CHUGWATER AND GOOSE EGG FORMATIONS (north Wyoming). 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. GOOSE EGG FORMATION--Red sandstone and siltstone, white gypsum, halite, and purple to white dolomite and limestone; CHUGWATER FORMATION OR GROUP (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. GOOSE EGG FORMATION--Red sandstone and siltstone, white gypsum, halite, and purple to white dolomite and limestone.

Lithology: siltstone; sandstone; shale; conglomerate; evaporite; dolostone (dolomite); limestone

Metamorphosed mafic and ultramafic rocks (Archean) at surface, covers 0.1 % of this area

METAMORPHOSED MAFIC AND ULTRAMAFIC ROCKS. Teton Range--Rendezvous Metagabbro; 2,875 Ma or older. Gros Ventre Range--Hornblende gneiss and serpentinite. Wind River Range--Pillowed amphibolite, metagabbro, and ultramafic sills. Wind River Canyon (cutting through Owl Creek Mountains)--Amphibolite and felsic gneiss of volcanic origin. Older than 2,700 Ma. Bighorn and Granite Mountains--Amphibolite. Seminoe Mountains--Amphibolite of volcanic origin, komatiite, and metagabbro. Casper Mountain--Amphibolite and serpentinite. Laramie Mountains--Amphibolite of volcanic origin, komatiite(?), metagabbro, and ultramafic sills.

Lithology: metavolcanic rock

Metasedimentary rocks (Archean) at surface, covers 0.2 % of this area

METASEDIMENTARY ROCKS. Wind River Range--Metagraywacke, pelitic schist, metaconglomerate, graphitic schist, and iron-formation; local meta-andesite. At least 2,800 Ma. Seminoe Mountains (southeast end of Granite Mountains)--Pelitic schist, quartzite, and iron-formation. Casper Mountain (northwest extension of Laramie Mountains)--Felsic gneiss, quartzite, and iron-formation. Laramie Mountains--Pelitic schist, iron-formation, quartzite, marble, metaconglomerate, and metagraywacke.

Lithology: metasedimentary rock

Laramide Anorthosite Complex--pyroxene and hornblende syenite (Proterozoic | Mesoproterozoic) at surface, covers 0.1 % of this area

LARAMIE ANORTHOSITE COMPLEX--Pyroxene and hornblende syenite--Age 1,435 Ma. In Laramie Mountains.

Lithology: anorthosite

Laramide Anorthosite Complex--anorthosite and norite (Proterozoic | Mesoproterozoic) at surface, covers 0.5 % of this area

LARAMIE ANORTHOSITE COMPLEX--Anorthosite and norite. In Laramie Mountains.

Lithology: anorthosite; norite

Upper Miocene Rocks (Phanerozoic | Cenozoic | Tertiary | Miocene-Late) at surface, covers 13 % of this area

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.

Lithology: sandstone; claystone; conglomerate; siltstone; limestone

Lower Miocene and Upper Oligocene rocks, or Rocks equivalent to Upper and Lower Miocene AND White River Formation (Phanerozoic | Cenozoic | Tertiary | Oligocene-Late Miocene-Early(?) Miocene-Middle(?) Miocene-Late) at surface, covers 30 % of this area

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.

Lithology: fine-grained mixed clastic; mixed clastic/volcanic

Granitic rocks (Archean) at surface, covers 0.8 % of this area

GRANITIC ROCKS OF 2,600-Ma AGE GROUP. 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.

Lithology: granitoid

Mowry and Thermopolis Shales (Phanerozoic | Mesozoic | Cretaceous-Early) at surface, covers < 0.1 % of this area

MOWRY (Kmr) AND THERMOPOLIS SHALES. MOWRY SHALE (AGE 94 TO 98 Ma)--Silvery-gray hard siliceous shale containing abundant fish scales and bentonite beds. THERMOPOLIS SHALE--Black soft fissile shale; Muddy Sandstone Member at top.

Lithology: shale; sandstone; mixed clastic/volcanic

Wells and Amsden Formations (TB), or Casper Formation and Madison Limestone (N, S) (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian-Early Pennsylvanian-Middle(?) Pennsylvanian-Late(?) Permian) at surface, covers 2 % of this area

WELLS AND AMSDEN FORMATIONS (Thrust Belt). WELLS FORMATION--Gray limestone interbedded with yellow limy sandstone. AMSDEN FORMATION--Red and gray cherty limestone and shale, sandstone, and conglomerate. CASPER FORMATION AND MADISON LIMESTONE (north, south Wyoming). CASPER FORMATION--Gray, tan, and red thick-bedded sandstone underlain by interbedded sandstone and pink and gray limestone. May include some Devonian(?) sandstone along east flank of Laramie Mountains. MADISON LIMESTONE--Includes Mission Canyon Limestone (blue-gray massive limestone and dolomite), underlain by Lodgepole Limestone (gray cherty limestone and dolomite).

Lithology: limestone; sandstone; shale; conglomerate; dolostone (dolomite)

Cloverly and Morrison Formations (N,S) or Cloverly Formation, Inyan Kara Group, and Morrison Formation (Phanerozoic | Mesozoic | Jurassic-Late Cretaceous-Early) at surface, covers 0.9 % of this area

CLOVERLY FORMATION and MORRISON FORMATION. 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; CLOVERLY FORMATION (Hartville uplift) or INYAN KARA GROUP (Black Hills) and MORRISON FORMATION. CLOVERLY FORMATION--Rusty to light-gray sandstone containing lenticular chert-pebble conglomerate interbedded with variegated bentonitic claystone. INYAN KARA GROUP--Rusty to light-gray sandstone containing lenticular chert-pebble conglomerate interbedded with variegated bentonitic claystone. Includes Fall River and Lakota Formations. MORRISON FORMATION, in northeast Wyoming, dully variegated siliceous claystone, nodular white limestone, and gray silty sandstone.

Lithology: sandstone; claystone; conglomerate; limestone

Granitic rocks (Proterozoic | Paleoproterozoic ) at surface, covers < 0.1 % of this area

GRANITIC ROCKS OF 1,700-Ma AGE GROUP.

Lithology: granitoid

White River Formation (Phanerozoic | Cenozoic | Tertiary | Oligocene (31-35 Ma)) at surface, covers 11 % of this area

WHITE RIVER FORMATION (AGE 31 TO 35 Ma)--White to pale-pink blocky tuffaceous claystone and lenticular arkosic conglomerate.

Lithology: fine-grained mixed clastic; medium-grained mixed clastic; mixed clastic/volcanic

White River Formation--Upper conglomerate member (Phanerozoic | Cenozoic | Tertiary | Oligocene ) at surface, covers 5 % of this area

WHITE RIVER FORMATION Upper conglomerate member--Light-gray soft conglomeratic tuffaceous sandstone and conglomerate of Precambrian clasts.

Lithology: medium-grained mixed clastic; conglomerate; mixed clastic/volcanic

Guernsey Formation (Phanerozoic | Paleozoic | Devonian-Late Carboniferous Mississippian-Early) at surface, covers 0.2 % of this area

GUERNSEY FORMATION--Blue-gray massive cherty limestone and dolomite. Locally includes unnamed dolomite and sandstone of Devonian and Cambrian(?) age.

Lithology: limestone; dolostone (dolomite); sandstone

Conglomerate (Phanerozoic | Cenozoic | Tertiary Quaternary | Miocene Pliocene(?) Pleistocene) at surface, covers < 0.1 % of this area

CONGLOMERATE--Northwest Wyoming (Jackson Hole) (Pleistocene or Pliocene)--Paleozoic clasts, chiefly of Madison Limestone, in a lithified carbonate matrix; Central (Medicine Bow Mountains) and east Wyoming (east of Laramie Mountains) (Pleistocene to Miocene)--Giant granite boulders in an arkose matrix.

Lithology: conglomerate

Granite gneiss (Archean) at surface, covers 2 % of this area

GRANITE GNEISS (AGE 2,600 TO 3,100+ Ma)--Layered to massive, locally migmatitic; metasedimentary and metavolcanic rocks locally common. Includes Webb Canyon Gneiss in Teton Range.

Lithology: granitic gneiss

Hartville Formation (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian-Early Pennsylvanian-Middle(?) Pennsylvanian-Late(?) Permian) at surface, covers 5 % of this area

HARTVILLE FORMATION--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.

Lithology: sandstone; carbonate; shale

Sherman Granite (Proterozoic | Mesoproterozoic (1415-1435 Ma)) at surface, covers 1 % of this area

SHERMAN GRANITE (AGE 1,415 TO 1,435 Ma)--In Medicine Bow and Laramie Mountains.

Lithology: granite

Cloverly, Morrison, and Sundance Formations (Phanerozoic | Mesozoic | Jurassic-Middle Jurassic-Late(?) Cretaceous-Early) at surface, covers 0.2 % of this area

CLOVERLY, MORRISON, AND SUNDANCE (Js) FORMATIONS. 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--Greenish-gray glauconitic sandstone and shale, underlain by red and gray nonglauconitic sandstone and shale.

Lithology: fine-grained mixed clastic; medium-grained mixed clastic; limestone; mixed clastic/volcanic; conglomerate