USGS Home
Contact USGS
Search USGS

Mineral Resources > Online Spatial Data > Geology > by state > Colorado Geology

Geologic units in San Juan county, Colorado

[Additional scientific data in this geographic area]

Rhyolitic intrusive rocks and flows of late-volcanic bimodal suite (Phanerozoic | Cenozoic | Tertiary) at surface, covers < 0.1 % of this area

Lithology: rhyolite

Glacial drift (Phanerozoic | Cenozoic | Quaternary) at surface, covers 2 % of this area

Includes some unclassified glacial deposits

Lithology: glacial drift

Pre-ash-flow andesitic lavas, breccias, tuffs, and conglomerates (Phanerozoic | Cenozoic | Tertiary) at surface, covers 9 % of this area

Includes several named units

Lithology: andesite; tuff; volcanic breccia (agglomerate)

Gravels and alluviums (Phanerozoic | Cenozoic | Quaternary) at surface, covers 0.5 % of this area

Includes Broadway and Louviers Alluviums

Lithology: gravel; alluvium

Mancos Shale (Phanerozoic | Mesozoic | Cretaceous) at surface, covers 0.2 % 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 Frontie

Lithology: shale; sandstone

Dolores Fm (Phanerozoic | Mesozoic | Triassic) at surface, covers 1 % of this area

Red siltstone, shale, sandstone, and limestone-pellet conglomerate

Lithology: siltstone; shale; sandstone; conglomerate

Intra-ash flow andesitic lavas (Phanerozoic | Cenozoic | Tertiary) at surface, covers 22 % of this area

Lithology: andesite

Ash-flow tuff of main volcanic sequence (Phanerozoic | Cenozoic | Tertiary) at surface, covers 6 % of this area

Includes many named units

Lithology: ash-flow tuff

Uncompahgre Fm (Proterozoic | Paleoproterozoic Mesoproterozoic) at surface, covers 13 % of this area

Quartzite, slate, and phyllite

Lithology: quartzite; slate; phyllite

Middle Tertiary intrusive rocks (Phanerozoic | Cenozoic | Tertiary) at surface, covers 4 % of this area

Intermediate to felsic compositions

Lithology: plutonic rock (phanerit

Leadville, Gilman, Dyer, Parting, and Sawatch Fms in west-central and south-central. Leadville Limestone, Ouray Limestone, Elbert Fm, and Ignacio Quartzite in far southwest (Phanerozoic | Paleozoic | Cambrian Ordovician(?) Silurian(?) Devonian(?) Carboniferous) at surface, covers 1 % of this area

Elbert Fm: shale and sandstone.

Lithology: limestone; dolostone (dolomite); quartzite; sandstone; shale

Dakota Sandstone or Group (Phanerozoic | Mesozoic | Cretaceous) at surface, covers 0.5 % of this area

Lithology: sandstone

Landslide deposits (Phanerozoic | Cenozoic | Quaternary) at surface, covers 0.2 % of this area

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

Lithology: landslide; talus; colluvium

Cutler Fm (Phanerozoic | Paleozoic | Permian) at surface, covers 11 % of this area

Arkosic sandstone, siltstone, and conglomerate

Lithology: sandstone; siltstone; conglomerate

Morrison, Wanakah, and Entrada Fms (Phanerozoic | Mesozoic | Jurassic) at surface, covers 2 % of this area

Lithology: mudstone; sandstone; limestone

Granitic rocks of 1400-m.y. age group (Proterozoic | Mesoproterozoic) 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

Lithology: granite; granodiorite; quartz monzonite

Felsic and hornblendic gneisses, either separate or interlayered (Proterozoic | Paleoproterozoic) at surface, covers 13 % of this area

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

Lithology: felsic gneiss; mafic gneiss; meta-basalt; meta-graywacke

Leadville Limestone, Gilman Sandstone, Dyer Dolomite, and Parting Fm (Phanerozoic | Paleozoic | Ordovician Silurian(?) Devonian) at surface, covers 0.1 % of this area

Parting Fm: quartzite and shale.

Lithology: limestone; sandstone; dolostone (dolomite); shale; quartzite

Eocene prevolcanic sedimentary rocks (Phanerozoic | Cenozoic | Tertiary) at surface, covers 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)

Lithology: sandstone; conglomerate; mudstone

Rico and Hermosa Fms (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian) at surface, covers 7 % of this area

Arkosic sandstone, conglomerate, shale, and limestone. Includes at base in some areas siltstone and shale of Molas Fm or Larsen Quartzite

Lithology: sandstone; conglomerate; shale; limestone; mudstone

Granitic rocks of 1700-m.y. age group (Proterozoic | Paleoproterozoic) at surface, covers 2 % 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;

Lithology: granite; granodiorite; quartz monzonite

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

Intermediate to felsic compositions

Lithology: plutonic rock (phanerit