Includes dune sand and silt and Peoria Loess
Loose to well-cemented sand and gravel
Includes Broadway and Louviers Alluviums
Intertongues complexly with units overlying Mesaverde Group or Formation; 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
Includes Slocum, Verdos, Rocky Flats, and Nussbaum Alluviums in east, and Florida, Bridgetimber, and Bayfield Gravels in southwest
Includes Piney Creek Alluvium and younger deposits
Includes metabasalt, metatuff, and interbedded metagraywacke; locally contains interlayered biotite gneiss. Derived principally from volcanic rocks
Sandstone and shale
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;
Alamosa Fm: gravel, sand, silt
Includes some unclassified glacial deposits
Sandstone and siltstone; west of Park Range
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
East: Ashy claystone and sandstone. Includes Castle Rock Conglomerate in region southeast of Denver. Northwest: Ashy claystone in North Park
Locally includes talus, rock-glacier, and thick colluvial deposits
Includes many named units
Calcareous shale and limestone
Sandstone, shale, and conglomerate. In northwest and west-central: Lower Cretaceous. In southwest: Lower and Upper Cretaceous.
Arkosic sandstone, shale, mudstone, conglomerate, and local coal beds
Includes basalts of Hinsdale Fm in San Juan Mountains - Servilleta Fm in San Luis Valley and many other occurrences
Sandstone and siltstone; in Piceance basin. Formerly Evacuation Creek Member of Green River Fm
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
Shale, claystone, sandstone, and major coal beds
Arkosic sandstone, conglomerate, and shale; coal in lower part; in North Park
Sandstone, shale, and major coal beds
Claystone, mudstone, sandstone, and conglomerate
Intermediate to felsic compositions
Includes Pikes Peak, Mount Rosa, Windy Point, and Redskin Granites and unnamed rocks
Summerville Fm: Shale and siltstone
Sharon Springs Member (organic-rich shale and numerous bentonite beds) in lower part
Claystone, mudstone, and sandstone; in Sand Wash basin
Includes several named units
Arkosic sandstone, siltstone, conglomerate, and local limestone
Shale, sandstone, marlstone, and limestone in Anvil Points, Garden Gulch, and Douglas Creek Members; in Piceance basin
Arkosic sandstone, siltstone, and shale; contains major coal deposits in Raton Basin
Kayenta Fm: red siltstone, shale, and sandstone. Chinle Fm: red siltstone and 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 sandstone, conglomerate, and shale. Includes Green Mountain Conglomerate south of Golden
Siltstone, sandstone, and conglomerate
Claystone, shale, and sandstone
Consists of Niobrara Formation (Kn) and either Benton Shale or Carlile, Greenhorn, and Graneros Fms (Kcg)
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.
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
Siltstone, shale, and sandstone
Parachute Creek Member--Oil shale, marlstone, and siltstone; in Piceance basin
Sandstone and shale. Trout Creek Sandstone Member at top; coal beds in upper half
Quartzite, conglomerate, and shale
Gypsum, siltstone, and shale; salt present in deep borings. Intertongues with Minturn and Lower Maroon Fms. Diapiric structure in many places
Arkosic sandstone, shale, and conglomerate; contains abundant volcanic materials; Upper Cretaceous volcaniclastic McDermott Member at base
Mainly intermediate to felsic compositions; some mafic
Arkosic sandstone, siltstone, and conglomerate
Claystone, oil shale, and sandstone; in Sand Wash basin
Arkosic sandstone, conglomerate, shale, and limestone. Includes at base in some areas siltstone and shale of Molas Fm or Larsen Quartzite
Claystone and mudstone; in Sand Wash basin
Arkosic conglomerate, sandstone, and shale
Siltstone, sandstone, and conglomerate. Includes Wagontongue Fm (Miocene) in South Park
Sandstone and siltstone; in Middle Park
Arkosic conglomerate, sandstone, and siltstone
Shale, sandstone, and local coal beds
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 (lime
Mainly of intermediate compositions
Morgan Fm: limestone, sandstone, and shale. In far northwest.
Sandstone and shale
Sandstone and shale
Shale and sandstone. Includes Farisita Conglomerate in northwestern Huerfano County
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
Parting Fm: quartzite and shale.
Sandstone and shale; major coal beds in lower part of Mount Garfield
In southwest, Glen Canyon Group consists of Navajo Sandstone, Kayenta Fm (red siltstone, shale, and sandstone) and Wingate Sandstone; Chinle is red siltstone
Claystone and oil shale; in Sand Wash basin. In extreme northwest includes rocks of Wilkins Peak Member
Arkosic sandstone and conglomerate
Sandstone, mudstone, claystone, and conglomerate; Denver is characterized by andesitic materials
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
Shale, limestone, and sandstone. Includes Kerber Fm in south-central
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
Gabbro and mafic diorite and monzonite
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)
Arkosic sandstone and shale, volcaniclastic conglomerate, and andesite flows and breccia
Burro Canyon is locally absent
Red sandstone, siltstone, and local limestone
Variegated claystone, mudstone, sandstone, and local beds of limestone
In extreme southwestern Moffat County, includes thin wedge of Carmel Fm (red siltstone and sandstone) beneath Entrada
Red siltstone, shale, and sandstone
Red siltstone and sandstone
Shale and sandstone
Shale, sandstone, and major coal beds
Upper part includes equivalents of Upper Mississippian Doughnut and Humbug Fms (shale, limestone, and sandstone)
In isolated patches that may not all be of the same age
Red siltstone, shale, sandstone, and limestone-pellet conglomerate
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)
Quartzite, slate, and phyllite
Carbonaceous shale and marlstone; in Sand Wash basin
Elbert Fm: shale and sandstone.
Mudstone, sandstone, and carbonaceous shale; in Sand Wash basin
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
Mainly Lower Cretaceous, Jurassic, and Triassic Fms
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
Red and gray siltstone, shale, and sandstone
Quartzite, conglomerate, and interlayered mica schist
Alkalic and mafic intrusive rocks in small plutons, and diabase dikes
Fremont Limestone, Harding Sandstone, and Manitou Limestone
sandstone, shale, and coal; sandstone
Arkosic sandstone, conglomerate, shale, and limestone; gypsum and salt in Paradox Member present in salt anticlines near Utah border
Dotsero Fm: Dolomite, in White River plateau only. Peerless Fm: sandstone and dolomite.
In Gunnison River area east of wedgeout of all units of Wanakah Fm (Jmw) except the Junction Creek Member
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
Includes Loveland Loess
Mainly as in Mesozoic unit (MZ) plus Permian and Pennsylvanian Fms
Sundance Fm: Sandstone, shale, claystone, and limestone
Sandstone, shale, and major coal beds
Along southern Grand Hogback, Chinle is represented only by basal Gartra Sandstone Member
Ralston Creek Fm: Claystone, sandstone, limestone, and gypsum
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.
Red siltstone, mudstone, sandstone, and local gypsum
Wanakah Fm: Sandstone, shale, limestone, and local gypsum
Red siltstone, sandstone, and conglomerate
Locally includes Peerless Fm
In northwestern San Juan Mountains. Cimarron Ridge Fm: volcanic breccia and conglomerate.
Alkalic and mafic rocks in small plutons, and diabase and gabbro dikes
Red siltstone, shale, and limestone
San Jose Formation; Eocene, San Juan Basin
In dikes and plugs
Morrison Fm: Variegated claystone, mudstone, sandstone, and local beds of limestone. Curtis Fm: glauconitic sandstone and limestone
METASEDIMENTARY AND METAVOLCANIC ROCKS. Sierra Madre--Granite gneiss, felsic gneiss, amphibolite, and metavolcanic rocks. Medicine Bow Mountains--Granite gneiss, felsic gneiss, amphibolite, and hornblende gneiss. Laramie Mountains--Pelitic schist, marble, granite gneiss, layered amphibolite, and felsic gneiss. Black Hills--Pelitic schist; includes minor amounts of granite and amphibolite.
SHERMAN GRANITE (AGE 1,415 TO 1,435 Ma)--In Medicine Bow and Laramie Mountains.
CHUGWATER FORMATION (north, northeast Wyoming)--Red siltstone and shale. Alcova Limestone Member in upper middle part in north Wyoming. Thin gypsum partings near base in north and northeast Wyoming. [None mapped in the NE]; CHUGWATER FORMATION OR GROUP (south Wyomingt)--Red shale and siltstone containing thin gypsum partings near base. Group includes Popo Agie Formation (red shale and red, yellow, and purple siltstone; lenses of lime-pellet conglomerate), Crow Mountain Sandstone (red and gray, thick bedded), Alcova Limestone, and Red Peak Formation (red siltstone and shale). Chugwater Formation includes as members all the units listed above. Includes overlying Jelm Formation in Shirley and Seminoe Mountains and at northern end of Laramie Basin. JELM FORMATION--Red sandstone.
WHITE RIVER FORMATION (AGE 31 TO 35 Ma)--White to pale-pink blocky tuffaceous claystone and lenticular arkosic conglomerate.
Cliff House Sandstone; transgressive marine sandstone; Campanian
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
Animas Formation; in northeast San Juan Basin
WASATCH FORMATION Main body--Drab sandstone, drab to variegated claystone and siltstone; locally derived conglomerate around basin margins. Lower part is Paleocene.
CASPER AND FOUNTAIN FORMATIONS. CASPER FORMATION--Gray, tan, and red thick-bedded sandstone underlain by interbedded sandstone and pink and gray limestone. May include some Devonian(?) sandstone along east flank of Laramie Mountains. FOUNTAIN FORMATION--Arkose and red sandstone.
Dakota Group of east-central and northeast New Mexico; in ascending order, Mesa Rica Sandstone, Pajarito Shale, and Romeroville Sandstone; includes the underlying Tucumcari Shale in Tucumcari area and Glencairn Formation in Union County. Encompasses both Upper and Lower Cretaceous rocks
Basalt and andesite flows; Neogene. Includes flows interbedded with Santa Fe and Gila Groups
CLOVERLY, MORRISON, AND SUNDANCE (Js) FORMATIONS. CLOVERLY FORMATION--Rusty sandstone at top, underlain by brightly variegated bentonitic claystone; chert-pebble conglomerate locally at base. MORRISON FORMATION--Dully variegated claystone, nodular limestone, and gray silty sandstone. In southern Yellowstone and Jackson Hole areas the presence of Morrison is questionable. SUNDANCE FORMATION--Greenish-gray glauconitic sandstone and shale, underlain by red and gray nonglauconitic sandstone and shale.
GRANITIC ROCKS OF 1,700-Ma AGE GROUP.
UPPER MIOCENE ROCKS--Southwest Wyoming: South end of Wind River Range--Siliceous, arkosic, and locally radioactive sandstone, claystone, and conglomerate. Fission-track age about 27 Ma. Recent work suggests that part of these deposits may be of Eocene age. Pliocene and Miocene (as originally defined 2) South Pass Formation. Saratoga Valley--White to greenish-gray tuffaceous sandstone, siltstone, and claystone; locally conglomeratic. North Park Formation; Central Wyoming: Arkosic sandstone, conglomerate, and siltstone; some light-colored tuffaceous radioactive claystone and white cherty limestone. North of Sweetwater River in Granite Mountains--Light-colored tuffaceous radioactive claystone, siltstone, sandstone, and arkose. Moonstone Formation; East Wyoming: Light-colored tuffaceous claystone, sandstone, and conglomerate. Ogallala Formation in Denver Basin.
GRAVEL, PEDIMENT, AND FAN DEPOSITS--Mostly locally derived clasts. Includes some glacial deposits along east flank of Wind River Range. Locally includes some Tertiary gravels.
Lewis Shale; marine shale and mudstone
unconsolidated sand, silt, clay, and gravel
Metaquartzite, amphibolite, and mica schist. Present only in small area at Utah border in Uinta Mountains
Pictured Cliffs Sandstone; prominent cliff-forming marine sandstone
MIOCENE ROCKS--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.
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.
unconsolidated dune sand
ALLUVIUM AND COLLUVIUM--Clay, silt, sand, and gravel in flood plains, fans, terraces, and slopes.
Kirtland and Fruitland Formations; coal-bearing, coal primarily in the Fruitland; Campanian to Maastrichtian
Landslide deposits and colluvium
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.
Mesaverde Group includes the Gallup Sandstone, Crevasse Canyon Formation, Point Lookout Sandstone, Menefee Formation, and Cliff House Sandstone
Mancos Shale; divided into Upper and Lower parts by Gallup Sandstone
Poison Canyon Formation; Paleocene, Raton Basin
CIMARRON- Buff to light-brown, fine- to medium-grained, thin bedded to massive sandstone with interbedded shales.
CIMARRON- Varicolored fine-grained sandstone, limestone, dolomite, shale, and conglomerate 0 to 470 +/- feet thick.
Morrison Formation and upper San Rafael Group
GLACIAL DEPOSITS--Till and outwash of sand, gravel, and boulders.
Lower Oligocene and Eocene volcanic rocks, undifferentiated; dominantly intermediate composition, with interbedded volcaniclastic rocks; (31-44 Ma)
Tertiary intrusive rocks; undifferentiated
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.
MAFIC INTRUSIVE ROCKS. Sierra Madre--Gabbro of Elkhorn Mountain; age 1,800 Ma. Medicine Bow Mountains--Mullen Creek 5 and Lake Owens 7 Mafic Complexes; older than 1,700 Ma.
JELM AND CHUGWATER FORMATIONS, FORELLE LIMESTONE, AND SATANKA SHALE. CHUGWATER FORMATION OR GROUP--Red shale and siltstone containing thin gypsum partings near base. Group includes Popo Agie Formation (red shale and red, yellow, and purple siltstone; lenses of lime-pellet conglomerate), Crow Mountain Sandstone (red and gray, thick bedded), Alcova Limestone, and Red Peak Formation (red siltstone and shale). Chugwater Formation includes as members all the units listed above. Includes overlying Jelm Formation in Shirley and Seminoe Mountains and at northern end of Laramie Basin. JELM FORMATION--Red sandstone. FORELLE LIMESTONE--Thin-bedded limestone. Locally is a member of the Goose Egg Formation. SATANKA SHALE--Red shale.
GREEN RIVER FORMATION Luman Tongue--Oil shale, carbonaceous shale, and sandstone.
CHUGWATER AND GOOSE EGG FORMATIONS (north Wyoming). CHUGWATER FORMATION--Red siltstone and shale. Alcova Limestone Member in upper middle part in north Wyoming. Thin gypsum partings near base in north and northeast Wyoming. GOOSE EGG FORMATION--Red sandstone and siltstone, white gypsum, halite, and purple to white dolomite and limestone; CHUGWATER FORMATION OR GROUP (south Wyoming)--Red shale and siltstone containing thin gypsum partings near base. Group includes Popo Agie Formation (red shale and red, yellow, and purple siltstone; lenses of lime-pellet conglomerate), Crow Mountain Sandstone (red and gray, thick bedded), Alcova Limestone, and Red Peak Formation (red siltstone and shale). Chugwater Formation includes as members all the units listed above. Includes overlying Jelm Formation in Shirley and Seminoe Mountains and at northern end of Laramie Basin. JELM FORMATION--Red sandstone. GOOSE EGG FORMATION--Red sandstone and siltstone, white gypsum, halite, and purple to white dolomite and limestone.
Raton Formation; in Raton Basin; unit contains conformable K/T boundary
Alluvium; upper and middle Quaternary
Menefee Formation; mudstone, shale, and sandstone; coal-bearing
Morrison Formation; Upper Jurassic nonmarine rocks present only in northern one-third of state
Dakota Sandstone; includes Oak Canyon, Cubero, and Paguate Tongues plus Clay Mesa Tongue of Mancos Shale; Cenomanian
Entrada Sandstone, Middle Jurassic; Callovian
FORELLE LIMESTONE AND SATANKA SHALE. FORELLE LIMESTONE--Thin-bedded limestone. Locally is a member of the Goose Egg Formation. SATANKA SHALE--Red shale .
BASALT FLOWS AND INTRUSIVE IGNEOUS ROCKS (AGE ABOUT 11 Ma).
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.
Ogallala Formation, alluvial and eolian deposits, and petrocalcic soils of the southern High Plains; Lower Pliocene to middle Miocene (locally includes unit Qoa)
WASATCH FORMATION Niland Tongue--Brown sandstone, carbonaceous shale, and coal.
FORT UNION FORMATION 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.
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.
Greenhorn FM- thin bedded gray, chalky limestone and calcareous shale. Graneros Shale- fissile, noncalcareous, gray shale locally contains sandstone and siltstone beds.
GREEN RIVER FORMATION Laney Member (age probably about 45 Ma)--Oil shale and marlstone.
chalky shale with bentonite and thick chalk beds, dark gray fissile shale containing septarian concretions, and fine-grained sandstone.
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.
Chinle Group; Upper Triassic; includes Moenkopi Formation (Middle Triassic) at base in many areas; in eastern part of state the following five formations are mapped:
GREEN RIVER FORMATION Tipton Shale Member or Tongue--Oil shale and marlstone.
Paleogene sedimentary units; includes Baca, Galisteo, El Rito, Blanco Basin, Love Ranch, Lobo, Sanders Canyon, Skunk Ranch, Timberlake, and Cub Mountain Formations
LEWIS SHALE (AGE ABOUT 68 Ma)--Gray marine shale containing many gray and brown lenticular concretion-rich sandstone beds.
GREEN RIVER FORMATION Wilkins Peak Member (age about 49 Ma)--Green, brown, and gray tuffaceous sandstone, shale, and marlstone; contains evaporites in subsurface sections.
Lower Oligocene silicic pyroclastic rocks (ash-flow tuffs); includes Hell's Mesa, Kneeling Nun, lower part of Bell Top Formation, Caballo Blanco, Datil Well, Leyba Well, Rock House Canyon, Blue Canyon, Sugarlump and Tadpole Ridge Tuffs, the tuffs of the Organ cauldron, Treasure Mountain Tuff (now known as Chiquito Peak Tuff), Bluff Creek Tuff, Oak Creek Tuff, tuff of Steins Mountain, tuff of Black Bill Canyon, tuff of Farr Ranch, Woodhaul Canyon, Gillespie and Box Canyon Tuffs, Cooney Tuff, and other volcanic and interbedded fluvial and pumiceous units; (31-36.5 Ma)
Graneros Shale and Greenhorn Formation; limited to northeastern area; lower Turonian and Cenomanian
Piedmont alluvial deposits: upper and middle Quaternary; includes deposits of higher gradient tributaries bordering major stream valleys, alluvial veneers of the piedmont slope, and alluvial fans