(Thrust Belt) Main body--Variegated red to gray, brown, and gray mudstone and sandstone; conglomeratic lenses. (in southwest Wyoming) - Drab to variegated claystone and siltstone, carbonaceous shale and coal, buff sandstone, arkose, and conglomerate. In northwestern part of Green River Basin is thick arkosic light-yellowish-tan sandstone intertonguing with pale-green to gray claystone and shale. (in east Wyoming) - Drab sandstone and drab to variegated claystone; numerous coal beds in lower part.
Clay, silt, sand, and gravel in flood plains, fans, terraces, and slopes.
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.
(Northern Yellowstone area) - Gray to brown shale and siltstone. (North and South Wyoming) - Dull-gray shale, gray siltstone, and fine-grained gray sandstone.
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.
Oil shale and marlstone.
Mostly locally derived clasts. Includes some glacial deposits along east flank of Wind River Range. Locally includes some Tertiary gravels.
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.
Southwest Wyoming: Southern Rock Springs uplift--Pale-green to tan tuffaceous sandstone and claystone of Miocene(?) age. Conglomerate of uncertain correlation locally at base. Saratoga Valley and west and southwest to Colorado--White massive soft tuffaceous sandstone and lesser amounts of white marl; lower part conglomeratic. Underlies North Park Formation in Saratoga Valley. To the west and southwest is called Browns Park Formation. Rawlins area--White massive soft tuffaceous sandstone; Central Wyoming: White soft tuffaceous sandstone. Locally derived conglomerate in upper and lower parts of sequence; in places lower conglomeratic sequence may be of Oligocene age. In Granite Mountains K/Ar age of tuff in lower part of sandstone sequence about 17 Ma and fission-track age of lower conglomerate about 24 Ma.
Includes active and dormant sand dunes. In northwestern Wyoming is chiefly loess (age 12,000-19,000 years).
(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.
Greenish-gray, olive-drab, and white tuffaceous sandstone and claystone; lenticular marlstone and conglomerate.
Dark-gray clay shale and concretionary sandstone.
Variegated claystone, shale, and sandstone; some lenticular gold-bearing quartzite conglomerate.
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.
(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.
White to pale-pink blocky tuffaceous claystone and lenticular arkosic conglomerate.
Till and outwash of sand, gravel, and boulders.
Drab sandstone, drab to variegated claystone and siltstone; locally derived conglomerate around basin margins. Lower part is Paleocene.
Soft gray sandstone, gray and brown carbonaceous shale, and thin coal beds.
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.
Light-gray volcanic conglomerate and white tuff, containing clasts of igneous rocks.
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).
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.
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.
(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.
Locally includes intermixed landslide and glacial deposits, talus, and rock-glacier deposits.
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.
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.
Thick beds of yellow sandstone interbedded with gray and black shale and many coal beds.
Mostly alluvium, colluvium, and glacial and landslide deposits. Primarily in Yellowstone area and Bighorn Mountains.
Layered to massive, locally migmatitic; metasedimentary and metavolcanic rocks locally common. Includes Webb Canyon Gneiss in Teton Range.
Equivalent to, and lithologically similar to locally derived basin-margin conglomerate of Wasatch Formation; merges southward into main body of Wasatch Formation. Lower part is Paleocene.
Andesitic volcaniclastic rocks.
Dark-gray concretionary marine shale; contains several bentonite beds.
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.
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.
New Fork Tongue - dull-red and green mudstone, brown sandstone, and thin limestone beds, merging southward in T. 23 N. with other units. Wasatch and Fontenelle Tongue or Member - oil shale, marlstone, limestone, and siltstone; occurs along Green and New Fork Rivers and on west side of Green River Basin from T. 33 N. south to and lensing out in T. 17 N.) of Green River.
Wind River Range--Largely granite gneiss; contains diorite and quartz diorite facies. Bighorn Mountains--Quartz diorite to quartz monzonite. Age 2,900+ Ma.
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.
Gray soft marine shale containing numerous bentonite beds and thin lenticular sandstone.
Variegated claystone and lenticular sandstone; conglomeratic near south margin of Wind River Range.
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.
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.
Gray, green, tan, and dull-red tuffaceous arkosic sandstone and claystone.
Gray marine shale containing many gray and brown lenticular concretion-rich sandstone beds.
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.
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.
Brown and gray sandstone, shale, conglomerate, and coal; giant quartzite boulders near Medicine Bow Mountains.
In Medicine Bow and Laramie Mountains.
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.
Stump Formation - Glauconitic siltstone, sandstone, and limestone. Preuss Sandstone or Redbeds - Purple, maroon, and reddish-gray sandy siltstone and claystone; contains salt and gypsum in thick beds in some subsurface sections. Twin Creek Limestone - Greenish-gray shaly limestone and limy siltstone. Includes Gypsum Spring Member.
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.
Light-gray soft conglomeratic tuffaceous sandstone and conglomerate of Precambrian clasts.
Newcastle Sandstone - Gray sandstone and sandy shale containing some bentonite and coal. Skull Creek Shale - Black soft fissile shale.
Green River Formation (Thrust Belt) - Buff laminated marlstone and limestone, brown oil shale, and siltstone. Includes Angelo and Fossil Butte Members. Wasatch Formation (Thrust Belt) - Variegated mudstone and sandstone. Includes Tunp and Bullpen Members, other tongues and unnamed members, and main body (variegated red to gray, brown, and gray mudstone and sandstone; conglomerate lenses). Green River Formation (in southwest Wyoming) - Oil shale, light-colored tuffaceous marlstone, and sandstone. Wasatch Formation (in southwest Wyoming) - Drab to variegated claystone and siltstone, carbonaceous shale and coal, buff sandstone, arkose, and conglomerate. In northwestern part of Green River Basin is thick arkosic light-yellowish-tan sandstone intertonguing with pale-green to gray claystone and shale.
Pale-pink to white blocky tuffaceous claystone and lenticular sandstone. Locally includes the Upper Conglomerate Member (Twru).
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.
(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. (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 (primarily cherty dolomite, limestone, and phosphatic gray shale) and Shedhorn Sandstone.
Tongue River (Tftr) - Thick beds of yellow sandstone interbedded with gray and black shale and many coal beds. Lebo Member (Tfl) - Dark-gray clay shale and concretionary sandstone.
Equigranular; locally gneissic.
Red, gray, and brown mudstone and conglomerate and yellow sandstone. La Barge Member tongues out to north at about T. 35 N. Lower part of Chappo is Paleocene.
Chiefly clay, silt, and fine sand. Includes travertine deposits.
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.
Light-colored limestone and gray to yellow speckled limy shale.
Ankareh Formation - Red and maroon shale and purple limestone. Thaynes Limestone - Gray limestone and limy siltstone. Woodside Shale - Red siltstone and shale. Dinwoody Formation - Gray to olive-drab dolomitic siltstone.
Light-gray to dark-red tuffaceous claystone, sandstone, and lenticular conglomerate.
Red sandy mudstone, sandstone, and chert-pebble conglomerate; thin limestone and dark-gray shale in upper part, more conglomeratic in lower part. Includes Smoot Formation (red mudstone and siltstone), Draney Limestone, Bechler Conglomerate, Peterson Limestone, and Ephraim Conglomerate. Upper Jurassic fossils have been reported from the Ephraim.
Wells Formation (Thrust Belt) - Gray limestone interbedded with yellow limy sandstone. Amsden Formation (Thrust Belt) - Red and gray cherty limestone and shale, sandstone, and conglomerate. Casper Formation (North and South Wyoming) - 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 (North and South Wyoming) - Includes Mission Canyon Limestone (blue-gray massive limestone and dolomite), underlain by Lodgepole Limestone (gray cherty limestone and dolomite).
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.
Light-colored sandstone and gray sandy shale containing marine fossils.
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).
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.
Group includes Mission Canyon Limestone (blue-gray massive limestone and dolomite), underlain by Lodgepole Limestone (gray cherty limestone and dolomite).
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.
Wilkins Peak Member - green, brown, and gray tuffaceous sandstone, shale, and marlstone; contains evaporites in subsurface sections. Tipton Shale Member or Tongue - oil shale and marlstone.
Anorthosite and norite. In Laramie Mountains.
Oil shale and marlstone.
Green and olive-drab hard generally well bedded andesitic conglomerate, sandstone, and claystone.
Red shale, red siltstone, and white gypsum beds; gypsum beds especially abundant near base.
Rock Springs uplift. White to brown sandstone, shale, and claystone; numerous coal beds.
Green, brown, and gray tuffaceous sandstone, shale, and marlstone; contains evaporites in subsurface sections.
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.
Diamictite grades laterally into other members of the formation.
Red sandstone and siltstone, white gypsum, halite, and purple to white dolomite and limestone.
Lavender to gray-brown welded rhyolite tuff.
Buff and red limy sandstone; some thin limestone beds, solution breccias, and gypsum.
Trout Peak Trachyandesite.
Light- to dark-gray siliceous tuffaceous shale and siltstone, thin bentonite beds, and quartzitic sandstone.
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.
Fox Hills Sandstone (Kfh) - Light-colored sandstone and gray sandy shale containing marine fossils. Lewis Shale (Kle) - Gray marine shale containing many gray and brown lenticular concretion-rich sandstone beds.
Rock Springs uplift. Drab-yellow and brown sandstone and sandy shale.
Includes Lookout Mountain Conglomerate Member of Wasatch Formation. On the south side of Gros Ventre Range consists of gold-bearing quartzite conglomerate; intertongues southward with sandstone and claystone of main body of Wasatch Formation.
(Thrust Belt) - Buff to pink crossbedded well-sized and well-sorted quartz sandstone and quartzite; locally has oil and copper-silver-zinc mineralization. (North Wyoming) - Gray to dull-red, crossbedded quartz sandstone.
Dark-gray to tan claystone, siltstone, and sandy shale.
Nugget Sandstone (Thrust Belt) - Buff to pink crossbedded well-sized and well-sorted quartz sandstone and quartzite; locally has oil and copper-silver-zinc mineralization. Nugget Sandstone (North Wyoming) - Gray to dull-red, crossbedded quartz sandstone. Ankareh Formation - Red and maroon shale and purple limestone. Thaynes Limestone - Gray limestone and limy siltstone. Woodside Shale - Red siltstone and shale. Dinwoody Formation (Thrust Belt) - Gray to olive-drab dolomitic siltstone. Dinwoody Formation (North Wyoming) - Olive-drab hard dolomitic thin-bedded siltstone. 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.
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.
Gray to black soft sandy shale and shaly sandstone.
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.
Minnekahta Limestone - Gray slabby hard limestone. Locally is a member of the Goose Egg Formation. Opeche Shale - Red soft sandy shale. Locally is a member of the Goose Egg 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.
Light-gray tuff, arkosic sandstone, and lenticular conglomerate.
Rock Springs uplift. White and brown soft sandstone, gray sandy shale, coal, and carbonaceous shale.
Gold-bearing quartzite conglomerate, olive-drab sandstone, and green claystone.
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.
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.
Brown and gray sandstone and shale; thin coal and carbonaceous shale beds.
Sage Junction Formation - Gray and tan siltstone and sandstone. Quealy Formation - Variegated mudstone and tan sandstone. Cokeville Formation - Tan sandstone, claystone, limestone, bentonite, and coal. Thomas Form Formation - Variegated mudstone and gray sandstone. Smiths Formation - Ferruginous black shale and tan to brown sandstone.
Brown and gray sandstone and shale; sparse carbonaceous shale and coal beds; thin lenses of pebble conglomerate.
Oil shale, carbonaceous shale, and sandstone.
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.
Chalky-white to gray sandstone, yellow, green, and dark-gray bentonitic claystone, white tuff, and thin coal beds.
Rock Springs uplift. White massive sandstone; lenticular chert-grit conglomerate in upper part.
Black shale, fine-grained brown sandstone, thin limestone, and bentonite beds.
Granitic rocks of 1,700-Ma Group
Brown sandstone, carbonaceous shale, and coal.
Brown gold-bearing quartzite conglomerate interbedded with brown and gray sandstone. Age of basal part about 67 Ma in northeastern Jackson Hole; farther south entire sequence is Paleocene.
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.
Gray to tan conglomeratic sandstone, siltstone, claystone, coal, and bentonite.
Clasts of red quartzite, gray chert, and limestone in a gray to white tuffaceous sandstone matrix.
Gray siltstone, sparse red sandstone, and lignite beds.
Light-colored tuffaceous sandstone and siltstone, locally conglomeratic. Locally designated by some as Norwood Tuff.
Steele Shale (Ks) - Gray soft marine shale containing numerous bentonite beds and thin lenticular sandstone. Niobrara Formation (Kn) - Light-colored limestone and gray to yellow speckled limy shale.
Partly consolidated gravel above and flanking some major streams.
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).
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.
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.
Madison Limestone or Group (North and South Wyoming) - Group includes Mission Canyon Limestone (blue-gray massive limestone and dolomite), underlain by Lodgepole Limestone (gray cherty limestone and dolomite). Darby Formation (North Wyoming) - Yellow and greenish-gray shale and dolomitic siltstone underlain by fetid brown dolomite and limestone. Bighorn Dolomite (North Wyoming) - Gray massive cliff-forming siliceous dolomite and locally dolomitic limestone. Gallatin Limestone or Group (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) - On south flank of Granite Mountains, blue-gray and yellow mottled hard dense limestone interbedded with soft green micaceous shale; dull-red quartzitic sandstone at bae. On and south of Rawlins uplift, glauconitic quartzitic sandstone. Minnekahta Limestone (Northeast Wyoming) - Gray slabby hard limestone. Locally is a member of the Goose Egg Formation. Opeche Shale (Northeast Wyoming) - Red soft sandy shale. Locally is a member of the Goose Egg Formation. Minnelusa Formation (Northeast Wyoming) - Buff and red limy sandstone; some thin limestone beds, solution breccias, and gypsum. Pahasapa Limestone (Northeast Wyoming) - Gray massive dolomititc limestone. Englewood Limestone (Northeast Wyoming) - Pink slabby dolomitic limestone. 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. Paleozoic Rocks, undifferentiated (Thrust Belt).
Drab nontuffaceous claystone, oil shale, lignite, and sandstone.
Wind River Range--Includes large bodies of metagabbro. Overprint pattern indicates area of migmatite related to emplacement of 2,600-Ma granite.
Interbedded drab and gray sandstone and claystone. Locally contains thick red and gray conglomerate.
In Medicine Bow Mountains and Sierra Madre. Deep Lake Group 3--Quartzite, diamictite, pelitic schist, and quartz-pebble conglomerate.
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.
Lebo Member (Tfl) - Dark-gray clay shale and concretionary sandstone. Tullock Member (Tft) - Soft gray sandstone, gray and brown carbonaceous shale, and thin coal beds.
Shear zone
Pyroxene and hornblende syenite--Age 1,435 Ma. In Laramie Mountains.
Felsic and mafic igneous bodies; the larger are mainly felsic.
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.
Dark-gray sandy shale; Sage Breaks Member at top; Turner Sandy Member in middle.
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).
In Medicine Bow Mountains and Sierra Madre. Libby Creek Group 3--Pelitic schist, amphibole schist, quartzite, diamictite, quartz-pebble conglomerate, and marble.
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.
White lacustrine clay, tuff, and limestone. In thrust belt includes conglomerate.
Giant boulders of granite in arkosic sandstone matrix. Reynolds (1976) considers age of eastern exposures to be Oligocene(?).
Lenticular gray and brown sandstone and shale; thin coal beds.
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.
Conglomerate of Paleozoic clasts, interbedded with drab sandstone and variegated claystone.
Sohare Formation (Kso) - Lenticular gray and brown sandstone and shale; thin coal beds. Bacon Ridge Sandstone (Kb) - Gray to tan marine sandstone and thick coal beds; gold-bearing quartzite conglomerate in lower part.
Including Trout Peak Trachyandesite, Wapiti Formation (andesitic volcaniclastic rocks), Crescent Hill Basalt, and Mount Wallace Formation (felsic and mafic volcaniclastic rocks).
Gray sandstone, siltstone, and carbonaceous claystone; conglomeratic in upper part; coal-bearing in lower part.
Sierra Madre--Encampment River Granodiorite 4; age 1,800 Ma. Medicine Bow Mountains--Keystone Quartz Diorite 5. Hartville uplift--Diorite of Twin Hills 6.
Wind River Formation (Central Wyoming (Twdr2)) - Variegated claystone and sandstone; lenticular conglomerate. Age of tuff at top 49 Ma. Indian Meadows Formation (Twim) - Red to variegated claystone, sandstone, and algal-ball(?) limestone; some beds of large Paleozoic boulders and detachment masses of Paleozoic and Mesozoic rocks.
Gypsum Spring Formation - Interbedded red shale, dolomite, and gypsum. In north Wyoming wedges out south in T. 39 N. Nugget Sandstone (JTRn) - gray to dull-red, crossbedded quartz sandstone.
Gray to tan marine sandstone and thick coal beds; gold-bearing quartzite conglomerate in lower part.
Incorporates masses of Mississippian through Cambrian formations. Confined to Black Hills.
Greenish-gray glauconitic sandstone and shale, underlain by red and gray nonglauconitic sandstone and shale.
Blue-gray massive cherty limestone and dolomite. Locally includes unnamed dolomite and sandstone of Devonian and Cambrian(?) age.
Light-gray sandstone interbedded with green and gray claystone; sparse coal and carbonaceous shale.
Forelle Limestone - Thin-bedded limestone. Locally is a member of the Goose Egg Formation. Satanka Shale - Red shale.
Red to variegated claystone, sandstone, and algal-ball(?) limestone; some beds of large Paleozoic boulders and detachment masses of Paleozoic and Mesozoic rocks.
Conglomerate of Precambrian clasts, interbedded with drab sandstone and claystone.
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. Nugget Sandstone (JTRn) - Gray to dull-red, crossbedded quartz sandstone.
Equivalent to Aycross (Ta) and Wind River (Twdr) Formations. Aycross Formation (Absaroka Volcanic Supergroup: Thorofare Creek Group) - 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. Wind River Formation - Variegated claystone and sandstone; lenticular conglomerate.
Northwest Wyoming (Bighorn Mountains): Gray soft poorly bedded to massive sandstone; Central Wyoming: Tuffaceous sandstone, siltstone, and white marl.
Mafic intrusive rocks
Reddish-brown conglomerate, chiefly of Paleozoic rock fragments.
Silvery-gray hard siliceous shale containing abundant fish scales and bentonite beds.
Gypsum Spring Formation - Interbedded red shale, dolomite, and gypsum. In north Wyoming wedges out south in T. 39 N. Nugget Sandstone (JTRn) - gray to dull-red, crossbedded quartz sandstone. 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.
Contains interbedded lithologies of Battle Spring (Tbs) and Wasatch (Tw2) Formations.
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.
Pahasapa Limestone - Gray massive dolomitic limestone. Englewood Limestone - Pink slabby dolomitic limestone.
Mafic volcaniclastic conglomerate and tuff; sparse claystone in upper part; gold-bearing quartzite conglomerate at base.
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. Nugget Sandstone (JTRn) - Gray to dull-red, crossbedded quartz sandstone.
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.
White, gray, and green limy tuff, siltstone, sandstone, and conglomerate.
Meeteetse Formation (Km) - Chalky-white to gray sandstone, yellow, green, and dark-gray bentonitic claystone, white tuff, and thin coal beds. Lewis Shale (Kle) - Gray marine shale containing many gray and brown lenticular concretion-rich sandstone beds.
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. Forelle Limestone - Thin-bedded limestone. Locally is a member of the Goose Egg Formation. Satanka Shale - Red shale.
Fox Hills Sandstone (Kfh) - Light-colored sandstone and gray sandy shale containing marine fossils. Bearpaw Shale - Dark-greenish-gray shale containing thin gray sandstone partings.
Upper 5,000 ft chiefly red conglomerate and red claystone; underlain by white tuff, limestone, claystone, and basal gray conglomerate.
Southeastern Montana: orangish brown, arkosic sandstone, lenticular conglomerate and siltstone, dark gray carbonaceous shale, coal, and varicolored claystone. Bears Paw Mountains: variegated red, pink, lavender, light green, yellow, gray, and very light gray shale, bentonitic claystone, and siltstone; light gray, brown, and green cross-bedded sandstone; and lenses of boulder conglomerate. Syntectonic alluvial fan and alluvial plain. Thickness as much as 120 m (394 ft) in Montana; upper part removed by erosion.
Locally derived clasts of Mesozoic and Paleozoic rocks in a red clay and sand matrix.
Giant granite boulders in arkosic sandstone matrix. Occurs along west margin of Wind River Range.
Tan to gray arkosic micaceous soft sandstone, claystone, and locally derived conglomerate.
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.
Leucite- and nepheline-rich flows, scoria, and necks.
In Laramie Mountains.
Dull-green and gray tuff, volcanic conglomerate, and sandstone.
Yellowish orange sandstone, sandy and silty carbonaceous shale, and coal. Alluvial plain. Thickness as much as 300 m (984 ft).
Lavender rhyolite welded tuff.
Dark-brown to black conglomerate, poorly bedded, composed chiefly of basalt clasts in a basaltic tuff matrix.
Massive to thin-bedded sandstone, mudstone, and shale.
Light-gray porphyritic rock.
Locally derived indurated angular conglomerate.
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.
Lacustrine white marl, claystone, sandstone, conglomerate, and tuff; generally radioactive.
Niobrara Formation (Kn) - Light-colored limestone and gray to yellow speckled limy shale. Frontier Formation (Kf) - Gray sandstone and sandy shale. 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.
Gray hard coarse-grained sandstone and conglomerate.
Greenish-gray bentonitic tuffaceous sandstone and conglomerate.
Marine and deltaic sandstone and shale of Cordilleran foreland basin (includes Gannett Group, Frontier, Mowry, Kootenay, and Thermopolis formations) in eastern Idaho thrust belt. (Paleocene to Neoproterozoic Sedimentary and Igneous Rocks of the Cordilleran System).
Light-gray thick-bedded finely crystalline dolomite.
Madison Limestone or Group - Group includes Mission Canyon Limestone (blue-gray massive limestone and dolomite), underlain by Lodgepole Limestone (gray cherty limestone and dolomite). Bighorn Dolomite - Light-gray massive siliceous dolomite.
Red and gray conglomerate containing clasts of Mesozoic, Paleozoic, and Precambrian rocks.
Gray to buff monzonite porphyry. Beartooth Mountains.
Basalt flows and intrusive igneous rocks
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.
Wayan Formation - Variegated mudstone, siltstone, and sandstone. Smiths Formation - Ferruginous black shale and tan to brown sandstone.
Quartzofeldspathic gneiss
Light- to greenish-gray porphyry.
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.
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.
Quartz monzonite of North Yellowstone
Greenish-gray to pink tuffaceous lacustrine and fluviatile claystone and siltstone, fine-grained sandstone, and conglomerate.
Gravel, sand, silt, and clay deposits of stream and river channels, and floodplains.
Dark to light gray, noncalcareous, partly silty or sandy shale with upper zone of white-weathering, calcareous concretions, middle zone of sandy, orange-weathering, calcareous concretions, and basal zone of ferruginous concretions. Marine. Thickness as much as 195 m (640 ft).
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).
Swift Formation (Jsw): Orangish brown, glauconitic, flaggy-bedded, commonly fossiliferous, fine-grained sandstone or sandy coquina with subordinate dark gray shale interbeds; chert pebbles common. In west-central and northwestern Montana, a dark gray, noncalcareous, micaceous shale forms the lower part of the formation, commonly with a basal chert-pebble conglomerate or conglomeratic sandstone as much as 3 m (10 ft) thick. Shallow marine. Thickness as much as 70 m (230 ft). Rierdon Formation (Jr): Gray, locally fossiliferous limestone that may contain floating grains of quartz sand, interbedded with greenish gray limy shale. Lagoonal and marine shelf. Thickness as much as 105 m (344 ft). Sawtooth Formation: Western Montana: dark gray, platy to shaly, dense limestone with local basal conglomerate. Central Montana: upper calcareous siltstone, middle dark gray shale with thin limestone interbeds, and lower fine-grained sandstone. Three local members Bowes, Firemoon, and Tampico, in descending order. Bowes Member: dark gray to medium gray, calcareous mudstone, limestone, and quartzose sandstone. Firemoon Member: dark to medium gray, limestone and calcareous mudstone. Tampico Member: very light gray, well-sorted quartz sandstone and siltstone, and chert-pebble conglomerate. Shallow marine. Thickness as much as 205 m (673 ft). Piper Formation (Jp): Upper part: red mudstone and gypsum; middle part: gray shale, limestone, and dolomite; lower part: red mudstone and gypsum. Marine and restricted coastal evaporite basins. Thickness as much as 75 m (246 ft).
Medicine Bow Mountains--Gaps Intrusion 3 (granitic). Hartville uplift--Granite and quartz monzonite of Flattop Butte 6; age 2,150+/- Ma.
Nonvolcanic conglomerate containing clasts of Lower Paleozoic rocks.
Abundant gray limestone and dolomite clasts and sparse rhyolite and quartzite clasts in a talc and clay matrix.
Marginal marine and marine sandstone and limestone; includes Nugget, Twin Creek, Preuss, Morrison, and Stump formations in eastern Idaho thrust belt. (Paleocene to Neoproterozoic Sedimentary and Igneous Rocks of the Cordilleran System).
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).
Variegated, yellow to red, gray to brown, pink to purple, and black, interbedded sandstone, siltstone, shale, limestone, dolomite, calcarenite, chert and brecciated beds. Thickness 394-1,175 ft (120-358 m).
Light gray to silvery gray, platy to blocky, siliceous shale and subordinate thin-bedded, gray siltstone or very fine-grained sandstone laminae or beds. Fish scales common in central Montana. Ledge-forming, chert-bearing, fine- to medium-grained sandstone at top throughout west-central Montana. Marine. Thickness 240 m (787 ft).
Older alluvial deposits
Kootenai Formation (Kk, Kku, Kkm, Kkl): Red, maroon, and olive gray mudstone, tan or gray siltstone, calcareous concretions, limestone beds, and several prominent sandstone beds that include the Greybull Member (top of the formation in south-central Montana) and the Sunburst Member (middle to lower part of the formation in northwest-central Montana), both dominantly quartzose sandstone. Basal Cutbank or Pryor Conglomerate. Alluvial plain with local marine influence in the north. Thickness as much as 335 m (1,099 ft).
Gray to black shale with ironstone concretions and numerous bentonite beds. Mosby Sandstone Member (upper part of formation in north- and east-central Montana): brown sandstone locally with chert pebbles, interbedded with gray shale. Big Elk Sandstone Member (lower part of formation in southwest-central Montana): light gray, chert-rich sandstone commonly stained dark red, interbedded with thin, dark gray to black clayey shale. Marine shelf. Thickness as much as 260 m (853 ft).
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).
Dacitic volcanic rocks; obsidian gravel at base.
Thermopolis Formation (Kt): Dark gray to black shale with subordinate siltstone beds. Middle part of formation contains one or more thin sandstone beds with chert pebble horizons where Muddy Sandstone is not present. Offshore marine. Thickness as much as 305 m (1,000 ft). Fall River Formation (Kfr): Gray and brown, fine- to medium-grained, quartzose sandstone with thin interbeds of dark gray shale. Nearshore marine. Thickness as much as 70 m (1,214 ft).
Gray to light gray calcareous shale and shaly marl with thin beds of limestone. Shale contains white to pink calcareous specks. Marine. Thickness as much as 100 m (30–75 ft).
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).
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).
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).
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.
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).
Alluvium and colluvium
Red siltstone, sandstone, and shale with subordinate gypsum and local limestone bed at top. Shallow restricted marine and nonmarine. Thickness as much as 180 m (590 ft).
Very light gray sandstone interbedded with subordinate carbonate, shale, and anhydrite. Cyclical marine, eolian, and sabkha. Thickness about 60 m (197 ft).
Clay to boulder-size clasts with locally abundant organic material. Thickness up to 75 ft (23m).
Claystone and oil shale; in Sand Wash basin. In extreme northwest includes rocks of Wilkins Peak Member
Red shale, light gray limestone, and cherty and sandy limestone. Coastal plain or marine. Thickness as much as 180 m (590 ft).
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).
Fluvial, fan, and lacustrine deposits and intercalated volcanic rocks of the Basin and Range Province (~16-2 Ma); consolidated to weakly consolidated sandstone, siltstone, arkose, conglomerate, mudstone, tuffaceous sediment, basalt, basaltic tephra, and rhyolite tuff. Includes deposits of Lake Idaho (Idaho Group) in western Snake River Plain and Salt Lake Formation deposited in Basin and Range Province of east-central Idaho. (Quaternary to Eocene Continental Sediments and Sedimentary Rocks).
Claystone, oil shale, and sandstone; in Sand Wash basin
Beirdneau Sandstone, Hyrum Dolomite, and Water Canyon Formation.
Deposits in valleys consisting of gravel, sand, and silt. Includes younger terrace deposits. May contain some glacial deposits and colluvium in uplands. (Quaternary Sediments).
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).
Gray and tan dolomite, cherty limestone, bedded chert, siltstone, sandstone, and gray to black phosphatic and dolomitic shale. Marine shelf and offshore marine. Thickness as much as 255 m (837 ft).
(North and South Wyoming) - Cody Shale (Kc2) - Dull-gray shale, gray siltstone, and fine-grained gray sandstone. Frontier Formation (Kf2) - Gray sandstone and sandy shale.
Wasatch Formation.
Light gray, bentonitic claystone that alternates with gray to brown sandstone interbedded with carbonaceous shale. Laterally equivalent to Lance Formation. Fluvial and flood plain. Thickness as much as 335 m (1,100 ft).
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.
Dark gray carbonaceous shale, bentonitic claystone, sandstone, and coal. Alluvial plain. Thickness as much as 185 m (607 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.
Green, gray, or red mudstone and marlstone with subordinate limestone and sandstone beds. Upper part Neocomian age in central Montana and contains carbonaceous black shale and coal. Fluvial, paludal, and lacustrine. Thickness as much as 180 m (590 ft).
Western Montana: gray, fine- to medium-grained, locally conglomeratic sandstone with interbeds of dark gray carbonaceous shale. Local conglomerate, porcellanite, and coal. Central Montana: dark gray, carbonaceous shale interbedded with siltstone and sandstone, chert-pebble conglomerate, and coal. Big Elk Sandstone Member: light gray, chert-rich sandstone commonly stained dark red, interbedded with thin, dark gray to black, clayey shale. Boulder River Sandstone Member: gray to greenish gray, very fine-grained to conglomeratic, glauconitic sandstone. Brackish to nonmarine. Thickness exceeds 2,135 m (7,005 ft) in Lima Peaks region, and exceeds 915m in the Greenhorn, Snowcrest, Gravelly, and Pioneer Mountains of southwestern Montana. Elsewhere thickness as much as 215 m (705 ft).
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).
Claystone, mudstone, and sandstone; in Sand Wash basin
Includes: Fall River Formation- Variegated brown, red, gray to purple, calcareous, well-sorted, fine-grained sandstone, siltstone, and shale containing mica flakes. Thickness 100-200 ft (30-61 m). Lakota Formation- Yellow, brown, red-brown, gray to black silty shale, pebble conglomerate, and massive to thin-bedded, cross-bedded sandstone. Locally interbedded with fresh-water limestone and bituminous coal beds. Thickness 35-500 ft (11-152 m).
Northern part of Wind River Basin. White-weathering oil-stained sandstone and brown carbonaceous shale.
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.
Thin interbeds of yellowish brown sandstone or siltstone and gray shale. Marine shoreface and offshore. Thickness as much as 200 m (656 ft).
Mowry Shale- Black to gray, siliceous, fissile shale and siltstone containing bentonite layers, and sparse sandstone dikes and sills. Thickness 125-250 ft (38-76 m). Newcastle Sandstone- Gray, light-brown to yellow, discontinuously distributed siltstone, claystone, sandy shale, and fine-grained sandstone. Thickness up to 290 ft (88 m). Skull Creek Shale- Dark-gray to blueish-gray shale containing ferruginous, and carbonate concretions. Thickness 150-275 ft (46-84 m).
Schist and gneiss
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).
Gray, ferruginous and glauconitic, fine- to coarse-grained sandstone, siltstone, and sandy to silty gray shale. Offshore marine. Pinches out laterally. Thickness as much as 100 m (328 ft).
Dark gray, partly silty shale with abundant bentonite beds and zones of gray, calcareous concretions. Marine. Thickness as much as650 m (2,133 ft). Only upper 50 m (164 ft) exposed.
Gravel and subordinate sand and silt deposited at mouths of canyons; largest fans are in Basin and Range Province in east-central and southeastern Idaho. (Quaternary Sediments).
Minnekahta Limestone-Purple to gray, finely crystalline, thin- to medium-bedded limestone with varying amounts of red shale. Thickness 30-50 ft (9-15 m). Opeche Shale- Red siltstone, argillaceous sandstone and shale interbedded with caliche layers. Thickness 85-130 ft (26-40 m).
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).
Fowkes Formation.
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).
Includes: Pahasapa Limestone (Mississippian)-White, light-gray to tan, fine- to medium-crystalline limestone and dolomite containing brown to gray chert. Solution features including collapse breccia, sinkholes, and caves are prevalent. Thickness 300-630 ft (91-192 m). Englewood Formation (Mississippian to Dovonian)- Pink, lavender to light-gray, thin- to medium-bedded, finely crystalline, argillaceous, dolomitic limestone. Thickness 30-63 ft (9-19 m).
Mudstone, sandstone, and carbonaceous shale; in Sand Wash basin
Wasatch/Colton Formations and Flagstaff Limestone.
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).
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).
Marine limestone of Mississippian carbonate banks and turbiditic sandstone, mudstone, and conglomerate of Antler flysch trough; includes Madison and Lodgepole formations and Chesterfield Range Group of southeastern Idaho; McGowan Creek Formation, White Knob Limestone, and overlying carbonate bank of Lost River Range; and Copper Basin Group of Pioneer Mountains. Includes poorly dated Salmon River assemblage east of Stanley, consisting of argillite, siltstone, calcareous sandstone, and limestone. (Paleocene to Neoproterozoic Sedimentary and Igneous Rocks of the Cordilleran System).
Claystone, shale, and sandstone
Sandstone and siltstone; west of Park Range
Chugwater Formation (TRc): Red siltstone, sandstone, and shale with subordinate gypsum and local limestone bed at top. Shallow restricted marine and nonmarine. Thickness as much as 180 m (590 ft). Goose Egg Formation: Red shale and sandstone with some interbeds of anhydrite, gypsum, and limestone. Nearshore marine, marine, and restricted marine. Thickness 30 m (98 ft).
Gray, siliceous mica schist and impure quartzite. Thickness undetermined.
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).
Weber Quartzite
Red sandy shale, siltstone, sandstone, and minor limestone. Interbedded with abundant gypsum. Thickness 328-559 ft (100-170 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).
Gardison and Lodgepole Limestones.
Morrison Formation (Late Jurassic)- Light-gray to green and variegatedred, brown, yellow, or lavender, silceous claystone, shale, and siltstone containing interbedded sandstone and fresh-water limestone lenses. Thickness up to 150 ft (46 m). Unkpapa Sandstone (Late Jurassic)- White, massive to thin-bedded, fine-grained, argillaceous sandstone. May be variegated to banded red, yellow, brown, or lavender. Thickness up to 267 ft (81 m). Sundance Formation (Late to Middle Jurassic)- Greenish-gray, yellow, tan, red to orange, and white, variegated, interbedded, fine- to coarse-grained sandstone, siltstone, clay, and limestone. Thickness 250-350 ft (76-107 m). Gypsum Springs Formation (Middle Jusassic)- Massive white gypsum and minor maroon siltstone and shale. Thickness up to 40 ft (12 m).
Wasatch and Evanston? Formations undivided.
Gneiss and amphibolite
Whitewood Limestone (Ordovician)- Mottled, tan, gray to lavender, fine- to medium-crystalline, sparsely fossiliferous limestone and dolomite. Thickness up to 70 ft (21 m). Winnipeg Formation (Ordovician)- Grat and light-green, fissile shale, and tan, calcareous siltstone, sandy shale, and limestone lenses. Thickness up to 110 ft (34 m). Deadwood Formation (Ordovician to Cambrian)- Variegated, yellow to red, brown, gray, and green, glauconitic, conglomerate, sandstone, shale, dolomitic limestone, and dolomite. Thickness 4-400 ft (1-122 m).
Dark gray to black shale with subordinate siltstone beds. Middle part of formation contains one or more thin sandstone beds with chert pebble horizons where Muddy Sandstone is not present. Offshore marine. Thickness as much as 305 m (1,000 ft).
Rhyolite tuffs, flows, and domes; includes Yellowstone Group (2.0-0.6 Ma) and isolated domes on Snake River Plain and north of Soda Springs (less than 2.0 Ma). (Quaternary to Eocene Continental Volcanic and Intrusive Rocks).
Till and outwash consisting of gravel, sand, silt, and clay. Formed by valley glaciers at higher elevations and by the Cordilleran ice sheet in northern Idaho. Includes deposits of several glacial episodes. Includes rock glacier deposits and some modern alluvium derived from reworked till and outwash. (Quaternary Sediments).
Three Forks Formation (MDt): Sappington Member (upper part of formation):yellowish orange and yellowish gray siltstone. Trident Member (middle part of formation): greenish gray and light olive gray, fossiliferous, calcareous shale that contains interbeds and nodules of fossiliferous, argillaceous limestone. Logan Gulch Member (lower part of formation): yellowish gray and grayish red, argillaceous limestone breccia and shale breccia that may include dolomitic siltstone. Marine to restricted marine with evaporite basins. Thickness as much as 185 m (607 ft). Jefferson Formation (Dj): Birdbear Member (upper part of formation): light to medium gray, sucrosic dolomite. Lower part of formation: grayish black, commonly petroliferous dolomite or limestone that may be interbedded with light gray quartzite. Marine. Thickness as much as 520 m (1,706 ft).
Dark-green amphibolite and amphibolite schist. Thickness of individual flows 50-200 ft (15-61 m).
Tan to reddish-brown, iron-stained stocks, laccoliths, sills, and dikes of trachyte, quartz trachyte, and alkalic rhyolite. Contains phenocrysts of sanidine, orrthoclase, anorthoclase, aegirine-augite and biotite in a finely crystalline orthoclase-quartz biotite groundmass.
Marine phosphorite, shale, and chert of Phosphoria Formation, fine-grained sandstone and mudrock of Wells, Quadrant, Amsden, and Shedhorn formations, and fine-grained sandstone, carbonaceous mudstone, and limestone of the Snaky Canyon Formation and Sun Valley and Oquirrh groups. Located in south-central and eastern Idaho. (Paleocene to Neoproterozoic Sedimentary and Igneous Rocks of the Cordilleran System).
Pilgrim Formation: Gray, commonly mottled limestone that may contain intraformational limestone conglomerate. Shallow marine. Thickness as much as 180 m (590 ft). Park Formation: Grayish green, fissile, micaceous shale with a few thin beds of calcareous sandstone and thin, gray limestone. Local arkose beds. Offshore marine. Thickness as much as 310 m (1,017 ft). Meagher Formation: Gray to bluish gray limestone and dolomitic limestone, locally mottled and with intraformational conglomerate beds. Shallow marine. Thickness as much as 300 m (984 ft). Wolsey Formation (CAw): Dark green and purplish gray fissile, micaceous shale, thin glauconitic limestone beds and thin, fine-grained sandstone beds. Shallow marine. Thickness as much as 145 m (476 ft). Flathead Formation (CAf): Pinkish gray to light gray sandstone or quartzite. Locally very glauconitic, pebbly, arkosic, or iron-stained. Marine shoreface. Thickness as much as 100 m (328 ft).
Orangish brown, glauconitic, flaggy-bedded, commonly fossiliferous, fine-grained sandstone or sandy coquina with subordinate dark gray shale interbeds; chert pebbles common. In west-central and northwestern Montana, a dark gray, noncalcareous, micaceous shale forms the lower part of the formation, commonly with a basal chert-pebble conglomerate or conglomeratic sandstone as much as 3 m (10 ft) thick. Shallow marine. Thickness as much as 70 m (230 ft).
Yellowish gray to very pale orange crystalline dolomite with local basal sandstone. Marine shelf. Thickness as much as 120 m (394 ft).
Upper part: red mudstone and gypsum; middle part: gray shale, limestone, and dolomite; lower part: red mudstone and gypsum. Marine and restricted coastal evaporite basins. Thickness as much as 75 m (246 ft).
Gray, locally fossiliferous limestone that may contain floating grains of quartz sand, interbedded with greenish gray limy shale. Lagoonal and marine shelf. Thickness as much as 105 m (344 ft).
Loose to well-cemented sand and gravel
East: Ashy claystone and sandstone. Includes Castle Rock Conglomerate in region southeast of Denver. Northwest: Ashy claystone in North Park
Clay to boulder-size clasts deposited as pediments, paleochannels, and terrace fills of former flood plains. Thickness up to 75 ft (23m).
Marine limestone, dolomite, and subordinate shale and sandstone of Cambrian carbonate bank of southeast Idaho stratigraphically up to St. Charles Formation and Ordovician Garden City Limestone. Includes Bayhorse succession (Cash Creek Quartzite, Garden Creek Phyllite, Bayhorse Dolomite, Ramshorn Slate, and Clayton Mine Quartzite) of Clayton area and Pioneer Mountains; quartzite of Kamiak Butte north of Moscow; and Cambrian Gold Creek quartzite, Rennie Shale, and Lakeview Limestone east of Bayview. (Paleocene to Neoproterozoic Sedimentary and Igneous Rocks of the Cordilleran System).