Includes dune sand and silt and Peoria Loess
Loose to well-cemented sand and gravel
In northwest and west-central: Intertongues complexly with units of overlying Mesaverde Group or Fm; lower part consists of a calcareous Niobrara equivalent and Frontier Sandstone and Mowry Shale Members; in areas where the Frontier and Mowry Members (Kmfm), or these and the Dakota Sandstone (Kfd) are distinguished, map unit (Km) consists of shale above Frontier Member. In Southwest: Lower part contains Juana Lopez Member (Kmj)
Includes Piney Creek Alluvium and younger deposits
Calcareous shale and limestone
Includes several named units
Includes Slocum, Verdos, Rocky Flats, and Nussbaum Alluviums in east, and Florida, Bridgetimber, and Bayfield Gravels in southwest
Sandstone, shale, and conglomerate. In northwest and west-central: Lower Cretaceous. In southwest: Lower and Upper Cretaceous.
Sandstone and shale
Includes Broadway and Louviers Alluviums
Locally contains minor hornblende gneiss, calc-silicate rock, quartzite, and marble. Derived principally from sedimentary rocks
Includes Boulder Creek -M.Y. AGE GROUP (AGE 1650-1730 M.Y.)--Includes Boulder Creek, Cross Creek, Denny Creek, Kroenke, Browns Pass, Powderhorn, Pitts Meadow, Bakers Bridge, and Tenmile Granites, Quartz Monzonites, or Granodiorites; also, unnamed granitic rocks
Includes metabasalt, metatuff, and interbedded metagraywacke; locally contains interlayered biotite gneiss. Derived principally from volcanic rocks
Carlile Shale, Greenhorn Limestone, and Graneros Shale
Includes many named units
Pierre Shale--Upper unit
Includes Silver Plume, Sherman, Cripple Creek, St. Kevin, Vernal Mesa, Curecanti, Eolus, and Trimble Granites or Quartz Monzonites; also, San Isabel Granite of Boyer (1962) and unnamed granitic rocks
Alamosa Fm: gravel, sand, silt
East: Ashy claystone and sandstone. Includes Castle Rock Conglomerate in region southeast of Denver. Northwest: Ashy claystone in North Park
Includes some unclassified glacial deposits
Summerville Fm: Shale and siltstone
Locally includes talus, rock-glacier, and thick colluvial deposits
Shale, claystone, sandstone, and major coal beds
Sandstone and siltstone; west of Park Range
Claystone, mudstone, sandstone, and conglomerate
Arkosic sandstone, conglomerate, and shale. Includes Green Mountain Conglomerate south of Golden
Includes basalts of Hinsdale Fm in San Juan Mountains - Servilleta Fm in San Luis Valley and many other occurrences
Includes Pikes Peak, Mount Rosa, Windy Point, and Redskin Granites and unnamed rocks
Sandstone and siltstone; in Piceance basin. Formerly Evacuation Creek Member of Green River Fm
Arkosic sandstone, shale, mudstone, conglomerate, and local coal beds
Pierre Shale, undivided
Claystone, shale, and sandstone
Arkosic sandstone, conglomerate, and shale; coal in lower part; in North Park
In Boulder-Fort Collins area, contains Richard, Larimer, Rocky Ridge, Terry, and Hygiene Sandstone Members; elsewhere shale between zones of Baculites reesidei and B. scotti
Intermediate to felsic compositions
Sandstone, shale, and major coal beds
Sharon Springs Member (organic-rich shale and numerous bentonite beds) in lower part
Arkosic sandstone, conglomerate, shale, and limestone. Includes Madera Fm and Sharpsdale Fm of Chronic (1958) in Sangre de Cristo Range and Gothic Fm of Langenheim (1952) in Elk Mountains. Other units of Middle Pennsylvanian age.
Shale, sandstone, marlstone, and limestone in Anvil Points, Garden Gulch, and Douglas Creek Members; in Piceance basin
In Moffat and Rio Blanco Counties, sandstone, shale, and coal beds above Sego Sandstone. Along Grand Hogback south of Colorado River, sandstone and shale above coal-bearing sequence
Claystone, mudstone, and sandstone; in Sand Wash basin
Arkosic sandstone, siltstone, conglomerate, and local limestone
Fox Hills Sandstone
In northwest and west-central: Major coal beds in lower part; Rollins Sandstone Member at base in Delta, Gunnison, and Pitkin Counties. In southwest: sandstone and shale.
Arkosic conglomerate, sandstone, and shale
Intra-ash flow andesitic lavas
Parachute Creek Member--Oil shale, marlstone, and siltstone; in Piceance basin
Arkosic sandstone, siltstone, and shale; contains major coal deposits in Raton Basin
Morrison, Wanakah, and Entrada Fms
Siltstone, sandstone, and conglomerate
Kayenta Fm: red siltstone, shale, and sandstone. Chinle Fm: red siltstone and sandstone
Morrison, Ralston Creek, and Entrada (or Exeter) Fms
Sandstone and shale. Trout Creek Sandstone Member at top; coal beds in upper half
Cliff House Sandstone
Arkosic conglomerate, sandstone, and siltstone
Arkosic sandstone, shale, and conglomerate; contains abundant volcanic materials; Upper Cretaceous volcaniclastic McDermott Member at base
Granitic rocks of 1400- and 1700-m.y. age groups, undivided, or, in Taylor River region, rocks with characteristics of Xg but U-Th-Pb zircon ages of Yg
Consists of Niobrara Formation (Kn) and either Benton Shale or Carlile, Greenhorn, and Graneros Fms (Kcg)
Lewis Shale
Gypsum, siltstone, and shale; salt present in deep borings. Intertongues with Minturn and Lower Maroon Fms. Diapiric structure in many places
Siltstone, shale, and sandstone
Minturn and Belden Fms
Sandstone and shale
Mainly intermediate to felsic compositions; some mafic
Quartzite, conglomerate, and shale
Arkosic sandstone, siltstone, and conglomerate
Pictured Cliffs Sandstone and Lewis Shale
Intra-ash flow quartz latitic lavas
Sandstone, mudstone, claystone, and conglomerate; Denver is characterized by andesitic materials
Weber Sandstone and Maroon Fm
Leadville Limestone, Williams Canyon Limestone , Manitou Limestone, and Sawatch Quartzite
Sandstone, shale, and coal; sandstone
Dakota Sandstone or Group
Arkosic sandstone, conglomerate, shale, and limestone. Includes at base in some areas siltstone and shale of Molas Fm or Larsen Quartzite
Claystone, oil shale, and sandstone; in Sand Wash basin
Shale, sandstone, and local coal beds
Claystone and mudstone; in Sand Wash basin
Sandstone and shale
Wingate Sandstone and Chinle Fm
Shale, sandstone, and minor coal beds; Fox Hills equivalent at base
Siltstone, sandstone, and conglomerate. Includes Wagontongue Fm (Miocene) in South Park
Sandstone and siltstone; in Middle Park
Dakota, Purgatoire, Morrison, Ralston Creek, and Entrada Fms in southeast. Dakota, Morrison, and Entrada Fms in central mountains. Dakota, Burro Canyon, Morrison, Wanakah, and Entrada Fms in Gunnison River area. Dakota, Morrison, Curtis, And Entrada Fm
Mainly of intermediate compositions
Northwest: includes Duchesne River Fm (sandstone and shale; includes some rocks of Eocene age) and Bishop Conglomerate near Utah border. South-central: includes Florissant Lake Beds (tuffaceous shale and tuff) and Antero Fm (limestone tuff, tuffaceous sandstone, and conglomerate). Southwest: includes Creede Fm (tuffaceous siltstone, sandstone, conglomerate) and gravels interbedded with volcanic rocks northeast and southeast of Gunnison
Morgan Fm: limestone, sandstone, and shale. In far northwest.
In southwest, Glen Canyon Group consists of Navajo Sandstone, Kayenta Fm (red siltstone, shale, and sandstone) and Wingate Sandstone; Chinle is red siltstone
Laramie Fm and Fox Hills Sandstone
Shale, limestone, and sandstone. Includes Kerber Fm in south-central
Shale and sandstone. Includes Farisita Conglomerate in northwestern Huerfano County
Dakota, Morrison, and Sundance Fms
Dotsero Fm: Dolomite, in White River plateau only. Peerless Fm: sandstone and dolomite.
Older glacial drift
Red siltstone, shale, sandstone, and limestone-pellet conglomerate
Parting Fm: quartzite and shale.
Weber Sandstone
Arkosic sandstone and conglomerate
Sandstone and shale; major coal beds in lower part of Mount Garfield
Claystone and oil shale; in Sand Wash basin. In extreme northwest includes rocks of Wilkins Peak Member
Shale, sandstone, and major coal beds; sandstone
Sandstone, siltstone, and conglomerate; in North Park and Laramie basin
Red and orange siltstone and sandstone
Red siltstone and sandstone
Gabbro and mafic diorite and monzonite
Ingleside Fm: Limestone and calcareous sandstone. Fountain Fm: arkosic sandstone and conglomerate
Volcaniclastic conglomerate interbedded with basalt flows of Hinsdale Fm (Tbb) on east flank of San Juan Mountains. Grades laterally into Santa Fe Fm of San Luis Valley
Gypsum, siltstone, and shale
Locally includes, at base, Burro Canyon Fm (shale and sandstone) or, in western Moffat County, Cedar Mountain Fm (conglomerate and shale)
In extreme southwestern Moffat County, includes thin wedge of Carmel Fm (red siltstone and sandstone) beneath Entrada
Arkosic sandstone and shale, volcaniclastic conglomerate, and andesite flows and breccia
Burro Canyon is locally absent
Red sandstone, siltstone, and local limestone
Leadville Limestone, Williams Canyon Limestone, and one or more of: Fremont Limestone, Harding Sandstone, and Manitou Limestone
Glen Canyon Sandstone; In northwest
Variegated claystone, mudstone, sandstone, and local beds of limestone
Pierre Shale (Kp), Niobrara (Kn), and Carlile, Greenhorn, and Graneros (Kcg) Fms, undivided
Quartzite, slate, and phyllite
Red siltstone, shale, and sandstone
Sego Sandstone, Buck Tongue of Mancos Shale, and Castlegate Sandstone
Red siltstone and sandstone
Shale and sandstone
Shale, sandstone, and major coal beds
In isolated patches that may not all be of the same age
Upper part includes equivalents of Upper Mississippian Doughnut and Humbug Fms (shale, limestone, and sandstone)
Curtis is absent along Grand Hogback
Marlstone, sandstone, and oil shale
South-central: Arkosic sand and bouldery gravel of Echo Park Alluvium. Southwest: includes Telluride Conglomerate and Blanco Basin Fm (arkosic mudstone, sandstone, and conglomerate)
Carbonaceous shale and marlstone; in Sand Wash basin
Elbert Fm: shale and sandstone.
Mudstone, sandstone, and carbonaceous shale; in Sand Wash basin
Ash-flow tuff of late-volcanic bimodal suite
Red siltstone, shale, and sandstone. Includes various combinations of Nugget, Jelm, Popo Agie, Chugwater, Red Peak, Forelle, Satanka, and Goose Egg Fms near Wyoming border
Early ash-flow tuff of Sawatch Range provenance
Sandstone; contains abundant volcanically derived material
Dakota Group and Morrison And Ralston Creek Fms at mountain front between Boulder and Colorado Springs. Dakota, Purgatoire, Morrison, and Ralston Creek Fms in Canon City area
Bouldery gravel on old erosion surfaces in Front Range and Never Summer Mountains
Mainly Lower Cretaceous, Jurassic, and Triassic Fms
Madison Limestone and Lodore Fm
Red siltstone, sandstone, and limestone-pellet conglomerate
Intermediate to felsic compositions
Siltstone, shale, and local gypsum
Calcareous sandstone; a thin but persistent unit distinguished only locally
Quartzite, conglomerate, and interlayered mica schist
Dakota and Morrison Fms
Red and gray siltstone, shale, and sandstone
In Gunnison River area east of wedgeout of all units of Wanakah Fm (Jmw) except the Junction Creek Member
Alkalic and mafic intrusive rocks in small plutons, and diabase dikes
Fremont Limestone, Harding Sandstone, and Manitou Limestone
Arkosic sandstone, conglomerate, shale, and limestone; gypsum and salt in Paradox Member present in salt anticlines near Utah border
Rhyolitic intrusive rocks and flows of late-volcanic bimodal suite
Lykins Fm and Lyons Sandstone
Morrison Fm and Entrada Sandstone
Shale and sandstone
Frontier Sandstone and Mowry Shale Members and intervening shale zone
Andesitic breccia and conglomerate
Sandstone, shale, and conglomerate
Red sandstone, siltstone, shale, and local limestone and gypsum
Calcareous siltstone and sandstone
Casper Fm: sandstone
Red siltstone, sandstone, and conglomerate
Siltstone, dolomite, and sandstone; in southeast
Chinle and Chugwater Fms
Ralston Creek Fm: Claystone, sandstone, limestone, and gypsum
Includes Loveland Loess
Mainly as in Mesozoic unit (MZ) plus Permian and Pennsylvanian Fms
Sundance Fm: Sandstone, shale, claystone, and limestone
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.
Sandstone, shale, and major coal beds
Along southern Grand Hogback, Chinle is represented only by basal Gartra Sandstone Member
Red siltstone, mudstone, sandstone, and local gypsum
Wanakah Fm: Sandstone, shale, limestone, and local gypsum
Basalt flows
Red siltstone, sandstone, and conglomerate
eolian silts
Red siltstone, shale, and limestone
Locally includes Peerless Fm
In northwestern San Juan Mountains. Cimarron Ridge Fm: volcanic breccia and conglomerate.
Dakota, Burro Canyon, Morrison, and Wanakah Fms
Alkalic and mafic rocks in small plutons, and diabase and gabbro dikes
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.
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.
Basaltic flows in Denver Fm near Golden
San Juan Basin
In dikes and plugs
Parting, Fremont, and Harding Fms
Morrison Fm: Variegated claystone, mudstone, sandstone, and local beds of limestone. Curtis Fm: glauconitic sandstone and limestone
In Medicine Bow and Laramie Mountains.
Eastern Uinta Basin Members of the Green River Formation (Evacuation Creek Mbr, Parachute Creek Mbr (oil shale), Garden Gulch Mbr, and Douglas Creek Mbr.).
Dakota Ss and Cedar Mtn or Burro Canyon Formations.
White to pale-pink blocky tuffaceous claystone and lenticular arkosic conglomerate.
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.
Transgressive marine sandstone.
San Juan Basin
Morrison Formation (Brushy Basin and Salt Wash Members).
Map unit includes Moenkopi Formation (Middle Triassic) at base in many areas; in eastern part of state the following five formations are mapped: TRr, TRb, TRt, TRg, and TRs.
Consists of Dakota Group, which includes Romeroville Sandstone (Cenomanian), Pajarito Shale, and Mesa Rica Sandstone (Albian); the underlying Tucumcari Shale (Albian) in Tucumcari area and Glencairn Formation (Albian) in Union County.
Glen Canyon Group (Navajo Ss, Kayenta Fm, and Wingate Ss). Includes Rainbow Bridge.
massive to cross-bedded, generally arkosic sand, silt and gravel, locally cemented with calcium carbonate; also contains limestone, volcanic ash, diatomaceous marl, opaline sandstone and bentonitic clay
Eolian deposits
Volcaniclastic sedimentary rocks of intermediate composition in northern San Juan Basin.
Clay, silt, sand, and gravel in flood plains, fans, terraces, and slopes.
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.
Drab sandstone, drab to variegated claystone and siltstone; locally derived conglomerate around basin margins. Lower part is Paleocene.
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.
Older alluvial deposits
Mesaverde Group.
Mancos Shale (Masuk Shale Mbr, Emery Sandstone Mbr, Blue Gate Shale Mbr, Ferron Sandstone Mbr, and Tununk Shale Mbr).
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.
Morrison Formation and upper San Rafael Group
Wasatch/Colton Formations and Flagstaff Limestone.
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.
Granitic rocks of 1,700-Ma Group
Williams Canyon Limestone, Manitou Limestone, and Sawatch Quartzite
Mudstone, shale, and sandstone; coal-bearing.
Mostly locally derived clasts. Includes some glacial deposits along east flank of Wind River Range. Locally includes some Tertiary gravels.
Uinta Mountain Group (24,000 feet thick along the Green River). Red Pine Shale (950 my).
Marine shale and mudstone.
Includes minor vent deposits and small shield volcanoes. Flows are commonly interbedded in the Santa Fe and Gila Groups.
Morgan Formation and Round Valley Limestone.
unconsolidated sand, silt, clay, and gravel
Distal sandstones, mudstones, and coal beds in eastern Raton Basin. Middle barren zone laterally equivalent to Poison Canyon Formation. K/T boundary discontinuously exposed about 100 m above basal conglomerate in area southwest of Raton.
Metaquartzite, amphibolite, and mica schist. Present only in small area at Utah border in Uinta Mountains
Alluvium and colluvium
CIMARRON- Buff to light-brown, fine- to medium-grained, thin bedded to massive sandstone with interbedded shales.
Proximal conglomerates and sandstones in western Raton Basin; generally lacking coal beds. Cretaceous beds mostly restricted to subsurface.
Prominent cliff-forming marine sandstone.
Bishop Conglomerate.
Schist, gneiss, and granite (1.5 billion years old).
CIMARRON- Fine- to medium-grained sand 0 to 40 feet thick. TEXAS- Fine to coarse windblown sand. Maximum thickness about 30 feet. BEAVER- Fine to coarse, round to sub-round, windblown sand consisting mostly of quartz grains. 0-50 feet thick.
Thin bedded gray to brownish gray shale; contains concretions, selenite crystals, thin beds of bentonite and locally chalky beds.
Landslide deposits on western flanks of Socorro Mountains not shown for clarity.
unconsolidated dune sand
Divided into Upper and Lower parts by Gallup Sandstone.
Duchesne River Fm, Uinta Formation (south of Uinta Mtns.) and Bridger Formation (north of Uinta Mtns.).
Coal-bearing, primarily in the Fruitland.
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.
Bluff Ss, Summerville Fm, Curtis Fm, Entrada Ss, and Carmel Formation. Includes Arches National Park.
Includes Cliff House Sandstone, Menefee Formation, and Point Lookout Sandstone.
Regressive marine sandstone in McKinley and Sandoval Counties; the lower, Hosta Tongue, of Point Lookout is transgressive and is separated from main body by the Satan Tongue of Mancos Shale.
Includes minor vent deposits. Flows are commonly interbedded in the Santa Fe and Gila Groups.
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.
CIMARRON- Varicolored fine-grained sandstone, limestone, dolomite, shale, and conglomerate 0 to 470 +/- feet thick.
Entrada Sandstone
Madison Limestone.
Till and outwash of sand, gravel, and boulders.
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.
Mostly intermediate lavas of the lower Datil Group and intermediate volcaniclastic sediments of the lower Spears Group (Tla+Tvs). Locally includes ash-flow tuffs of the upper Datil Group (Tlrp). Includes intermediate volcaniclastic sedimentary rocks of the Conejos Formation in northern New Mexico.
Includes many long basaltic andesite dikes of Oligocene age near Pie Town, Acoma, Riley, Chupadera, Truth or Consequences, Roswell, Raton, and Dulce; and several elongate or shoestring-like sills of basalt or basaltic andesite. Also includes basaltic necks of Pliocene age that dot the landscape northeast of Mount Taylor. Where dikes extend into Quaternary alluvium the contact is an unconformity.
Oil shale, carbonaceous shale, and sandstone.
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.
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.
Alluvium
Chinle Shale and Shinarump Conglomerate Member.
In southwest includes the basalt-bearing Broken Jug Formation.
Mancos Shale, lower part
Upper Jurassic nonmarine rocks.
CIMARRON- Kiowa Shale Member: Gray to black fossiliferous shale with sandstone in the upper part. Thickness ranges from 0 to 50 +/- feet. Cheyenne Sandstone Member: Massive, white to buff, fine- to medium-grained sandstone, containing some conglomerate in the lower part, from 0 to 120 +/- feet thick.
Includes deposits of higher gradient tributaries bordering major stream valleys, alluvial veneers of the piedmont slope, and alluvial fans. May locally include uppermost Pliocene deposits.
Includes Oak Canyon, Cubero, and Paguate Tongues; includes Clay Mesa Tongue of Mancos Shale.
Landslides
Includes Baca, Galisteo, El Rito, Blanco Basin, Hart Mine, Love Ranch, Lobo, Sanders Canyon, Skunk Ranch, Timberlake, and Cub Mountain Formations.
Lodore Sandstone.
Variegated claystone and lenticular sandstone; conglomeratic near south margin of Wind River Range.
Forelle Limestone - Thin-bedded limestone. Locally is a member of the Goose Egg Formation. Satanka Shale - Red shale.
CIMARRON- Clay, silt, sand, and gravel 0 to 100 feet thick. TEXAS- Sand, silt, clay, and gravel located in valleys of principal streams. Thickness not known but may exceed 100 feet in North Canadian River valley and may be 50 to 100 feet in lower parts of valleys of Coldwater and Palo Duro Creeks BEAVER - Sand, gravel, silt, and clay in discontinuous lenses along courses of larger streams. 0-50 feet thick.
Basalt flows and intrusive igneous rocks
Eolian deposits.
CIMARRON- Upper shale unit: Varicolored siltstone or claystone, conglomerate, fine-grained sandstone, and limestone. Lower sandstone unit: Varicolored, fine- to coarse-grained sandstone with some clay and interbedded shale.
Includes minor vent deposits. Flows are commonly interbedded in the Santa Fe and Gila Groups.
Brown sandstone, carbonaceous shale, and coal.
Alluvial and eolian deposits, and petrocalcic soils of the southern High Plains. Locally includes Qoa.
(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.
Greenhorn FM- thin bedded gray, chalky limestone and calcareous shale. Graneros Shale- fissile, noncalcareous, gray shale locally contains sandstone and siltstone beds.
CIMARRON- Generally semiconsolidated clay, silt, sand, gravel, and caliche 0 to 400 feet thick. BEAVER- Interbedded sand, siltstone, clay, gravel lenses, and thin limestone. Caliche common near surface but occurrence is not limited to the surface. Caliche accounts for most of the white color in the Ogallala. Other colors generally light tan or buff but locally may be pastel shades of almost any color. The Laverne and Rexroad Formations of Pliocene age and the Meade Group and Odee (of local usage) and other formations of Pleistocene age occur locally and are included with the Ogallala Formation, 0-700 feet thick. WOODWARD- Gravel, sand, silt, clay, caliche, and limestone, locally cemented with calcium carbonate. Generally light-tan to gray to white. Thickness ranges up to 400 feet and probably averages 150 feet. CLINTON- Gray to light-brown, fine- to medium-grained sand with some, clay, silt, gravel, volcanic ash, and caliche beds; locally cemented by calcium carbonate. Thickness ranges from 0 to about 320 feet. The formation thins eastward.
Cutler Group (White Rim Ss, De Chelly Ss, Organ Rock Shale, Cedar Mesa Ss, Halgaito Fm, and Elephant Canyon Fm). Includes Natural Bridges National Monument.
Oil shale and marlstone.
Browns Park Formation.
Morrison Formation (Dinosaur National Monument).
Weber Sandstone.
Dakota and Cedar Mountain Formations.
Chalky shale with bentonite and thick chalk beds, dark gray fissile shale containing septarian concretions, and fine-grained sandstone.
Mancos Shale (Hilliard Shale and Blair Formation north of Uinta Mountains), Frontier Ss, and Mowry Shale.
Curtis Fm, Entrada Ss, and Carmel Fm.
Oil shale and marlstone.
Broadly intertonguing conglomeratic sandstones, sandstones and mudstones; minor coal beds.
Park City Formation.
Gray marine shale containing many gray and brown lenticular concretion-rich sandstone beds.
Green, brown, and gray tuffaceous sandstone, shale, and marlstone; contains evaporites in subsurface sections.
Regional ash-flow tuffs include Hell's Mesa, Kneeling Nun, Caballo Blanco, Datil Well, Leyba Well, Rock House Canyon, Blue Canyon, Sugarlump, Oak Creek, Bluff Creek, Gillespie, Box Canyon, Cooney and Chiquito Peak Tuffs; the tuffs of Steins Mountain, Black Bill Canyon, Woodhaul Canyon, and Farr Ranch; tuffs of the Organ cauldron; and lower tuffs in the Bell Top Formation. Includes some locally erupted lavas and tuffs within thick intra-caldera units; includes minor volcaniclastic sedimentary units and lavas between thin outflow sheets.
Limited to northeastern area.