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

Geologic units in Rio Grande county, Colorado

[Additional scientific data in this geographic area]

Middle Tertiary intrusive rocks (Phanerozoic | Cenozoic | Tertiary) at surface, covers 0.6 % of this area

Intermediate to felsic compositions

Lithology: plutonic rock (phanerit

Ash-flow tuff of main volcanic sequence (Phanerozoic | Cenozoic | Tertiary) at surface, covers 22 % of this area

Includes many named units

Lithology: ash-flow tuff

Intra-ash flow andesitic lavas (Phanerozoic | Cenozoic | Tertiary) at surface, covers 5 % of this area

Lithology: andesite

Basalt flows and associated tuff, breccia, and conglomerate of late-volcanic bimodal suite (Phanerozoic | Cenozoic | Tertiary) at surface, covers 5 % of this area

Includes basalts of Hinsdale Fm in San Juan Mountains - Servilleta Fm in San Luis Valley and many other occurrences

Lithology: basalt; tuff; volcanic breccia (agglomerate); conglomerate

Unclassified surficial deposits and underlying Alamosa Fm in San Luis Valley (Phanerozoic | Cenozoic | Tertiary Quaternary) at surface, covers 28 % of this area

Alamosa Fm: gravel, sand, silt

Lithology: alluvium

Pre-ash-flow andesitic lavas, breccias, tuffs, and conglomerates (Phanerozoic | Cenozoic | Tertiary) at surface, covers 19 % of this area

Includes several named units

Lithology: andesite; tuff; volcanic breccia (agglomerate)

Los Pinos Fm (Phanerozoic | Cenozoic | Tertiary) at surface, covers 2 % of this area

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

Lithology: mixed clastic/volcanic; basalt

Glacial drift (Phanerozoic | Cenozoic | Quaternary) at surface, covers 0.4 % of this area

Includes some unclassified glacial deposits

Lithology: glacial drift

Rhyolitic intrusive rocks and flows of late-volcanic bimodal suite (Phanerozoic | Cenozoic | Tertiary) at surface, covers 0.7 % of this area

Lithology: rhyolite

Modern alluvium (Phanerozoic | Cenozoic | Quaternary) at surface, covers 8 % of this area

Includes Piney Creek Alluvium and younger deposits

Lithology: alluvium

Intra-ash flow quartz latitic lavas (Phanerozoic | Cenozoic | Tertiary) at surface, covers 4 % of this area

Lithology: quartz latite

Older gravels and alluviums (Phanerozoic | Cenozoic | Quaternary) at surface, covers 2 % of this area

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

Lithology: gravel; alluvium

Landslide deposits (Phanerozoic | Cenozoic | Quaternary) at surface, covers 4 % of this area

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

Lithology: landslide; talus; colluvium