Geologic units in Montrose county, Colorado

Additional scientific data in this geographic area

Dakota Sandstone and Burro Canyon Fm (Cretaceous) at surface, covers 37 % of this area

Sandstone, shale, and conglomerate. In northwest and west-central: Lower Cretaceous. In southwest: Lower and Upper Cretaceous.

Morrison Fm, Summerville Fm, and Entrada Sandstone (Jurassic) at surface, covers 24 % of this area

Summerville Fm: Shale and siltstone

Mancos Shale (Cretaceous) at surface, covers 12 % of this area

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)

Landslide deposits (Quaternary) at surface, covers 6 % of this area

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

Modern alluvium (Quaternary) at surface, covers 5 % of this area

Includes Piney Creek Alluvium and younger deposits

Glen Canyon Group and Chinle Fm (Jurassic-Triassic) at surface, covers 4 % of this area

In southwest, Glen Canyon Group consists of Navajo Sandstone, Kayenta Fm (red siltstone, shale, and sandstone) and Wingate Sandstone; Chinle is red siltstone

Gravels and alluviums (Quaternary) at surface, covers 2 % of this area

Includes Broadway and Louviers Alluviums

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

Kayenta Fm, Wingate Sandstone, and Chinle Fm (Triassic) at surface, covers 2 % of this area

Kayenta Fm: red siltstone, shale, and sandstone. Chinle Fm: red siltstone and sandstone

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

Includes dune sand and silt and Peoria Loess

Morrison, Wanakah, and Entrada Fms (Jurassic) at surface, covers 1 % of this area

Morrison, Wanakah, and Entrada Fms

Older gravels and alluviums (Quaternary) at surface, covers 0.6 % of this area

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

Pre-ash-flow andesitic lavas, breccias, tuffs, and conglomerates (Tertiary) at surface, covers 0.5 % of this area

Includes several named units

Chinle Fm (Triassic) at surface, covers 0.5 % of this area

Red siltstone, sandstone, and limestone-pellet conglomerate

Wingate Sandstone and Chinle Fm (Triassic) at surface, covers 0.5 % of this area

Wingate Sandstone and Chinle Fm

Moenkopi Fm and Cutler Fm (Triassic-Permian) at surface, covers 0.5 % of this area

Red siltstone and sandstone

Hermosa Fm (Pennsylvanian) at surface, covers 0.5 % of this area

Arkosic sandstone, conglomerate, shale, and limestone; gypsum and salt in Paradox Member present in salt anticlines near Utah border

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 (Early-Middle Proterozoic) at surface, covers 0.4 % of this area

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

Morrison Fm (Jurassic) at surface, covers 0.4 % of this area

Variegated claystone, mudstone, sandstone, and local beds of limestone

Morrison Fm and Wanakah Fm (Junction Creek Sandstone Member at or near top; Pony Express Limestone Member at base) (Jurassic) at surface, covers 0.3 % of this area

Wanakah Fm: Sandstone, shale, limestone, and local gypsum

Granitic rocks of 1400-m.y. age group (Middle Proterozoic) at surface, covers 0.2 % 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

Ash-flow tuff of main volcanic sequence (Tertiary) at surface, covers 0.2 % of this area

Includes many named units

Mesaverde Fm, undivided (Cretaceous) at surface, covers 0.1 % of this area

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.

Granitic rocks of 1700-m.y. age group (Early Proterozoic) at surface, covers 0.1 % 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

Telluride conglomerate of Eocene prevolcanic sedimentary rocks (Te) and Cimarron Ridge Fm (Tertiary-Cretaceous) at surface, covers < 0.1 % of this area

In northwestern San Juan Mountains. Cimarron Ridge Fm: volcanic breccia and conglomerate.

Dakota Ss and Cedar Mtn. or Burro Canyon Formations (Cretaceous) at surface, covers < 0.1 % of this area

Dakota Ss and Cedar Mtn or Burro Canyon Formations.

Morrison Formation (Brushy Basin and Salt Wash Members) (Late Jurassic) at surface, covers < 0.1 % of this area

Morrison Formation (Brushy Basin and Salt Wash Members).

Landslides (Quaternary) at surface, covers < 0.1 % of this area

Landslides

Bluff Ss, Summerville Fm, Curtis Fm, Entrada Ss, and Carmel Formation (Middle to Late Jurassic) at surface, covers < 0.1 % of this area

Bluff Ss, Summerville Fm, Curtis Fm, Entrada Ss, and Carmel Formation. Includes Arches National Park.

Glen Canyon Group (Early Jurassic) at surface, covers < 0.1 % of this area

Glen Canyon Group (Navajo Ss, Kayenta Fm, and Wingate Ss). Includes Rainbow Bridge.

Eocene prevolcanic sedimentary rocks (Tertiary) at surface, covers < 0.1 % of this area

South-central: Arkosic sand and bouldery gravel of Echo Park Alluvium. Southwest: includes Telluride Conglomerate and Blanco Basin Fm (arkosic mudstone, sandstone, and conglomerate)

Eolian deposits (Quaternary) at surface, covers < 0.1 % of this area

Eolian deposits