Geologic units in Jackson county, Colorado

Additional scientific data in this geographic area

Coalmont Fm (Tertiary) at surface, covers 35 % of this area

Arkosic sandstone, conglomerate, and shale; coal in lower part; in North Park

Felsic and hornblendic gneisses, either separate or interlayered (Early Proterozoic) at surface, covers 9 % of this area

Includes metabasalt, metatuff, and interbedded metagraywacke; locally contains interlayered biotite gneiss. Derived principally from volcanic rocks

Glacial drift (Quaternary) at surface, covers 7 % of this area

Includes some unclassified glacial deposits

Granitic rocks of 1700-m.y. age group (Early Proterozoic) at surface, covers 6 % of this area

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

Gravels and alluviums (Quaternary) at surface, covers 6 % of this area

Includes Broadway and Louviers Alluviums

Pierre Shale, undivided (Cretaceous) at surface, covers 6 % of this area

Pierre Shale, undivided

North Park Fm (Tertiary) at surface, covers 4 % of this area

Sandstone, siltstone, and conglomerate; in North Park and Laramie basin

Modern alluvium (Quaternary) at surface, covers 3 % of this area

Includes Piney Creek Alluvium and younger deposits

Volcanic rocks in northwestern Colorado (Tertiary) at surface, covers 3 % of this area

Mainly of intermediate compositions

Granitic rocks of 1400-m.y. age group (Middle Proterozoic) at surface, covers 3 % of this area

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

Colorado Group (Cretaceous) at surface, covers 3 % of this area

Consists of Niobrara Formation (Kn) and either Benton Shale or Carlile, Greenhorn, and Graneros Fms (Kcg)

Older gravels and alluviums (Quaternary) at surface, covers 3 % of this area

Includes Slocum, Verdos, Rocky Flats, and Nussbaum Alluviums in east, and Florida, Bridgetimber, and Bayfield Gravels in southwest

Landslide deposits (Quaternary) at surface, covers 2 % of this area

Locally includes talus, rock-glacier, and thick colluvial deposits

Dakota, Morrison, and Sundance Fms (Cretaceous-Jurassic) at surface, covers 2 % of this area

Dakota, Morrison, and Sundance Fms

Biotitic gneiss, schist, and migmatite (Early Proterozoic) at surface, covers 2 % of this area

Locally contains minor hornblende gneiss, calc-silicate rock, quartzite, and marble. Derived principally from sedimentary rocks

Eolian deposits (Quaternary) at surface, covers 1 % of this area

Includes dune sand and silt and Peoria Loess

Older glacial drift (Quaternary) at surface, covers 1 % of this area

Older glacial drift

Chugwater Fm (Triassic) at surface, covers 0.8 % of this area

Red sandstone, siltstone, shale, and local limestone and gypsum

White River Fm or Group (Tertiary) at surface, covers 0.7 % of this area

East: Ashy claystone and sandstone. Includes Castle Rock Conglomerate in region southeast of Denver. Northwest: Ashy claystone in North Park

Middle Tertiary intrusive rocks (Tertiary) at surface, covers 0.7 % of this area

Intermediate to felsic compositions

Mesozoic rocks (Lower Cretaceous-Triassic) at surface, covers 0.6 % of this area

Mainly Lower Cretaceous, Jurassic, and Triassic Fms

Triassic and Permian rocks (Triassic-Permian) at surface, covers 0.5 % of this area

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

Ash-flow tuff of main volcanic sequence (Tertiary) at surface, covers 0.4 % of this area

Includes many named units

Mafic rocks of 1700-m.y. age group (Early Proterozoic) at surface, covers 0.3 % of this area

Gabbro and mafic diorite and monzonite

Metasedimentary and metavolcanic rocks (Early Proterozoic) at surface, covers 0.2 % of this area

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.

Dakota Sandstone or Group (Cretaceous) at surface, covers < 0.1 % of this area

Dakota Sandstone or Group

Upper Miocene Rocks (Upper Miocene) at surface, covers < 0.1 % of this area

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.

Upper Tertiary intrusive rocks (Tertiary) at surface, covers < 0.1 % of this area

Intermediate to felsic compositions

Dakota and Morrison Fms (Cretaceous-Jurassic) at surface, covers < 0.1 % of this area

Dakota and Morrison Fms

Granitic rocks of 1,700-Ma Age Group (Early Proterozoic) at surface, covers < 0.1 % of this area

Granitic rocks of 1,700-Ma Group

Miocene Rocks (Miocene) at surface, covers < 0.1 % of this area

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.

Glacial deposits (Pleistocene-Holocene) at surface, covers < 0.1 % of this area

Till and outwash of sand, gravel, and boulders.

Alluvium and Colluvium (Pleistocene-Holocene) at surface, covers < 0.1 % of this area

Clay, silt, sand, and gravel in flood plains, fans, terraces, and slopes.