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

Geologic units in Albany county, Wyoming

Sherman Granite (Proterozoic | Mesoproterozoic (1415-1435 Ma)) at surface, covers 7 % 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 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

Medicine Bow Formation (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers 0.2 % of this area

MEDICINE BOW FORMATION--Brown and gray sandstone and shale; thin coal and carbonaceous shale beds.

Lithology: sandstone; shale; coal

Niobrara Formation (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers 2 % of this area

NIOBRARA FORMATION (AGE ABOUT 83 Ma)--Light-colored limestone and gray to yellow speckled limy shale.

Lithology: limestone; fine-grained mixed clastic

Lewis Shale (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers 2 % of this area

LEWIS SHALE (AGE ABOUT 68 Ma)--Gray marine shale containing many gray and brown lenticular concretion-rich sandstone beds.

Lithology: shale; sandstone

Madison Limestone or Group (S) (Phanerozoic | Paleozoic | Carboniferous Mississippian-Early Mississippian-Middle(?) Mississippian-Late) at surface, covers < 0.1 % 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).

Lithology: limestone; dolostone (dolomite)

Metasedimentary rocks: Deep Lake Group (Proterozoic | Paleoproterozoic ) at surface, covers < 0.1 % of this area

METASEDIMENTARY ROCKS--In Medicine Bow Mountains and Sierra Madre. Deep Lake Group 3--Quartzite, diamictite, pelitic schist, and quartz-pebble conglomerate.

Lithology: metasedimentary rock

Wind River Formation (Phanerozoic | Cenozoic | Tertiary | Eocene) at surface, covers 4 % of this area

WIND RIVER FORMATION Northwest Wyoming (Jackson Hole)--Variegated red and white claystone and siltstone; largely nontuffaceous except near the top; lenticular coal unit in middle. At base locally includes equivalent of Indian Meadows Formation; Central Wyoming--Variegated claystone and sandstone; lenticular conglomerate. Age of tuff at top 49 Ma.

Lithology: claystone; siltstone; sandstone; coal

Granite gneiss (Archean) at surface, covers 9 % 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

White River Formation--Upper conglomerate member (Phanerozoic | Cenozoic | Tertiary | Oligocene ) at surface, covers 0.2 % 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

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

White River Formation (Phanerozoic | Cenozoic | Tertiary | Oligocene (31-35 Ma)) at surface, covers 2 % 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

Granitic rocks (Proterozoic | Paleoproterozoic ) at surface, covers 0.3 % of this area

GRANITIC ROCKS OF 1,700-Ma AGE GROUP.

Lithology: granitoid

Lower Miocene Rocks (Phanerozoic | Cenozoic | Tertiary | Miocene-Early) at surface, covers < 0.1 % of this area

LOWER MIOCENE ROCKS--Northwest Wyoming (Bighorn Mountains): Gray soft poorly bedded to massive sandstone; Central Wyoming: Tuffaceous sandstone, siltstone, and white marl.

Lithology: sandstone; siltstone

Cloverly and Morrison Formations (N,S) or Cloverly Formation, Inyan Kara Group, and Morrison Formation (Phanerozoic | Mesozoic | Jurassic-Late Cretaceous-Early) at surface, covers 0.7 % 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

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)

Frontier Formation and Mowry and Thermopolis Shales (Phanerozoic | Mesozoic | Cretaceous-Early Cretaceous-Middle(?) Cretaceous-Late) at surface, covers 0.1 % of this area

FRONTIER FORMATION (Kf) AND MOWRY (Kmr) AND THERMOPOLIS SHALES. FRONTIER FORMATION--Gray sandstone and sandy shale. In Northern Yellowstone area, Yellowish- to medium-gray sandstone; tuffaceous and carbonaceous in lower part. 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: sandstone; shale; mixed clastic/volcanic

Mowry and Thermopolis Shales (Phanerozoic | Mesozoic | Cretaceous-Early) at surface, covers 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

Granitic rocks (Archean) at surface, covers 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

Steele Shale (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers 4 % of this area

STEELE SHALE (AGE ABOUT 78 TO 82 Ma)--Gray soft marine shale containing numerous bentonite beds and thin lenticular sandstone.

Lithology: shale; mixed clastic/volcanic; sandstone

Jelm and Chugwater Formations, Forelle Limestone, and Satanka Shale (Phanerozoic | Paleozoic Mesozoic | Permian Triassic-Early) at surface, covers 0.3 % of this area

JELM AND CHUGWATER FORMATIONS, FORELLE LIMESTONE, AND SATANKA SHALE. CHUGWATER FORMATION OR GROUP--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. FORELLE LIMESTONE--Thin-bedded limestone. Locally is a member of the Goose Egg Formation. SATANKA SHALE--Red shale.

Lithology: fine-grained mixed clastic; medium-grained mixed clastic; mixed clastic/carbonate; evaporite

Quartz diorite (Proterozoic | Paleoproterozoic ) at surface, covers 0.7 % of this area

QUARTZ DIORITE. Sierra Madre--Encampment River Granodiorite 4; age 1,800 Ma. Medicine Bow Mountains--Keystone Quartz Diorite 5. Hartville uplift--Diorite of Twin Hills 6.

Lithology: quartz diorite

Hanna Formation (Phanerozoic | Cenozoic | Tertiary | Paleocene ) at surface, covers 1 % of this area

HANNA FORMATION--Brown and gray sandstone, shale, conglomerate, and coal; giant quartzite boulders near Medicine Bow Mountains.

Lithology: medium-grained mixed clastic; fine-grained mixed clastic; conglomerate; coal

Frontier Formation (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers 2 % of this area

FRONTIER FORMATION in thrust belt--White to brown sandstone and dark-gray shale; oyster coquina in upper part; coal and lignite in lower part; in north and south Wyoming--Gray sandstone and sandy shale.

Lithology: sandstone; shale; coal

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 0.1 % 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

Upper Miocene Rocks (Phanerozoic | Cenozoic | Tertiary | Miocene-Late) at surface, covers 1 % 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

Playa lake and other lacustrine deposits (Phanerozoic | Cenozoic | Quaternary | Pleistocene Holocene) at surface, covers < 0.1 % of this area

PLAYA LAKE AND OTHER LACUSTRINE DEPOSITS--Chiefly clay, silt, and fine sand. Includes travertine deposits.

Lithology: playa; lake or marine deposit (non-glacial)

Laramide Anorthosite Complex--anorthosite and norite (Proterozoic | Mesoproterozoic) at surface, covers 6 % of this area

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

Lithology: anorthosite; norite

Laramide Anorthosite Complex--pyroxene and hornblende syenite (Proterozoic | Mesoproterozoic) at surface, covers 2 % of this area

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

Lithology: anorthosite

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

Mesozoic and Paleozoic rocks (Phanerozoic | Paleozoic Mesozoic | Carboniferous Mississippian-Late Pennsylvanian(?) Permian(?) Triassic(?) Jurassic(?) Cretaceous-Late) 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 in south--Gray to dull-red, massive to coarsely crossbedded quartz sandstone.

Lithology: sedimentary rock; clastic; mixed clastic/volcanic; mixed clastic/carbonate

Terrace gravel (Phanerozoic | Cenozoic | Tertiary Quaternary | Pliocene Pleistocene) at surface, covers < 0.1 % of this area

TERRACE GRAVEL (PLEISTOCENE AND/OR PLIOCENE)--Partly consolidated gravel above and flanking some major streams.

Lithology: gravel

Metamorphosed mafic and ultramafic rocks (Archean) at surface, covers 0.9 % 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

Chugwater and Goose Egg Formations (Phanerozoic | Paleozoic Mesozoic | Permian Triassic-Early(?) Triassic-Middle(?) Triassic-Late) at surface, covers 0.2 % 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

Forelle Limestone and Satanka Shale (Phanerozoic | Paleozoic | Permian) at surface, covers 0.5 % of this area

FORELLE LIMESTONE AND SATANKA SHALE. FORELLE LIMESTONE--Thin-bedded limestone. Locally is a member of the Goose Egg Formation. SATANKA SHALE--Red shale .

Lithology: limestone; shale

Mafic intrusive rocks (Proterozoic | Paleoproterozoic ) at surface, covers 0.6 % of this area

MAFIC INTRUSIVE ROCKS. Sierra Madre--Gabbro of Elkhorn Mountain; age 1,800 Ma. Medicine Bow Mountains--Mullen Creek 5 and Lake Owens 7 Mafic Complexes; older than 1,700 Ma.

Lithology: gabbroid

Casper and Fountain Formations (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian-Middle Pennsylvanian-Late Permian) at surface, covers 4 % of this area

CASPER AND FOUNTAIN FORMATIONS. 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. FOUNTAIN FORMATION--Arkose and red sandstone.

Lithology: sandstone; limestone

Chugwater Formation (N, NE), or Chugwater Formation or Group (S) (Phanerozoic | Mesozoic | Triassic-Early Triassic-Middle(?) Triassic-Late) at surface, covers 3 % 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

Glacial deposits (Phanerozoic | Cenozoic | Quaternary | Pleistocene Holocene) at surface, covers 0.8 % of this area

GLACIAL DEPOSITS--Till and outwash of sand, gravel, and boulders.

Lithology: glacial drift

Mesaverde Formation (N) or Mesaverde Group (S) (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers 1 % 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.

Lithology: sandstone; shale; coal; conglomerate

Wagon Bed Formation (Phanerozoic | Cenozoic | Tertiary | Eocene (45-49 Ma)) at surface, covers 3 % of this area

WAGON BED FORMATION (AGE ABOUT 45 TO 49 Ma)--Southwest and central Wyoming--Green and gray tuffaceous claystone, sandstone, and conglomerate; some uranium-phosphate marlstone and variegated bentonitic claystone. Locally contains oil shale between Wind River and Bighorn Basins; Central Wyoming (west side of Laramie Mountains)--Dull-green siliceous bentonitic claystone and tuff; giant granite boulder conglomerate in tuffaceous matrix.

Lithology: claystone; conglomerate; sandstone

Alluvium and Colluvium (Phanerozoic | Cenozoic | Quaternary | Pleistocene Holocene) at surface, covers 15 % of this area

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

Lithology: alluvium; colluvium

Casper Formation (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian-Middle Pennsylvanian-Late Permian) at surface, covers 0.8 % of this area

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.

Lithology: sandstone; limestone

Goose Egg Formation (Phanerozoic | Paleozoic Mesozoic | Permian Triassic-Early) at surface, covers 1.0 % 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)

Metasedimentary and metavolcanic rocks (Archean) at surface, covers 0.3 % 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

Dune sand and loess (Phanerozoic | Cenozoic | Quaternary | Pleistocene Holocene) at surface, covers < 0.1 % 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 rocks: Libby Creek Group (Proterozoic | Paleoproterozoic ) at surface, covers 0.3 % of this area

METASEDIMENTARY ROCKS--In Medicine Bow Mountains and Sierra Madre. Libby Creek Group 3--Pelitic schist, amphibole schist, quartzite, diamictite, quartz-pebble conglomerate, and marble.

Lithology: metasedimentary rock

Metasedimentary and metavolcanic rocks (Proterozoic | Paleoproterozoic ) at surface, covers 4 % of this area

METASEDIMENTARY AND METAVOLCANIC ROCKS. Sierra Madre--Granite gneiss, felsic gneiss, amphibolite, and metavolcanic rocks. Medicine Bow Mountains--Granite gneiss, felsic gneiss, amphibolite, and hornblende gneiss. Laramie Mountains--Pelitic schist, marble, granite gneiss, layered amphibolite, and felsic gneiss. Black Hills--Pelitic schist; includes minor amounts of granite and amphibolite.

Lithology: metasedimentary rock; metavolcanic rock

Sundance Formation (Phanerozoic | Mesozoic | Jurassic-Middle Jurassic-Late) at surface, covers 0.2 % of this area

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

Lithology: sandstone; shale

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

PERIDOTITE INTRUSIVE ROCKS--In Laramie Mountains.

Lithology: peridotite

Landslide deposits (Phanerozoic | Cenozoic | Quaternary | Pleistocene Holocene) at surface, covers 0.3 % of this area

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

Lithology: landslide; glacial drift

Gravel, pediment, and fan deposits (Phanerozoic | Cenozoic | Quaternary | Pleistocene Holocene) at surface, covers 6 % 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

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

Lithology: tectonite