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Oligocene sedimentary rocks

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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 (limestone tuff, tuffaceous sandstone, and conglomerate). Southwest: includes Creede Fm (tuffaceous siltstone, sandstone, conglomerate) and gravels interbedded with volcanic rocks northeast and southeast of Gunnison
State Colorado
Name Oligocene sedimentary rocks
Geologic age Tertiary
Lithologic constituents
Major
Sedimentary > Clastic > Sandstone (Tuffaceous)
Minor
Sedimentary > Clastic > Mudstone > Shale (Tuffaceous)
Igneous > Volcanic (Pyroclastic-tuff)
Sedimentary > Clastic > Conglomerate (Tuffaceous)
Incidental
Sedimentary > Clastic > Siltstone (Tuffaceous)
References

Tweto, Ogden, 1979, Geologic Map of Colorado: U.S. Geological Survey Special Geologic Map, scale 1:500,000.
NGMDB product
Counties Fremont - Gunnison - Mineral - Moffat - Park - Rio Blanco - Saguache - Teller