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Duff Formation (with Decie Member from Paisano caldera shown separately), Cottonwood Springs Basalt, Potato Hill Andesite, Sheep Canyon Basalt, Crossen Trachyte, and Pruett Formation, undivided

Duff Formation (with Decie Member from Paisano caldera shown separaetly), Cottonwood Springs Basalt, Potato Hill Andesite, Sheep Canyon Basalt, Crossen Trachyte, and Pruett Formation, undivided
State Texas
Name Duff Formation (with Decie Member from Paisano caldera shown separately), Cottonwood Springs Basalt, Potato Hill Andesite, Sheep Canyon Basalt, Crossen Trachyte, and Pruett Formation, undivided
Geologic age Phanerozoic | Cenozoic | Tertiary | Eocene-Late Oligocene-Early
Comments in west Brewster Co., rhyolitic tuff, minor sandstone, conglomerate and mafic flows, felsic flows, and flow breccia. mafic flows, anygdaloidal, vesicular, andesitic flow breccia, porphyritic mafic flows, thin tuff and nonmarine limestone, prophyritic quartz trachyte, tuff, tuffaceous sandstone, conglomerate breccia, tuffaceous nonmarine limestone. Pruett Fm., about 330 ft thick in Fort Stockton Sheet (1982), mostly volcanic tuff, some tuffaceous sandstone, conglo., breccia, and tuffaceous fresh-water limestone which interfingers with other units named in this map unit. Thickness more than 4,500 ft.
Primary rock type rhyolite
Secondary rock type basalt
Other rock types tuff; sandstone; conglomerate; limestone
Lithologic constituents
Major
Igneous > Volcanic > Felsic-volcanic > Rhyolite (Pyroclastic, ash-flow)
Minor
Igneous > Volcanic > Mafic-volcanic > Basalt
Igneous > Volcanic > Felsic-volcanic > Trachyte
Sedimentary > Clastic > Mixed-clastic > Siltstone-Mudstone
Incidental
Sedimentary > Carbonate > Limestone (Tuffaceous)
Sedimentary > Clastic > Sandstone (Tuffaceous)
Sedimentary > Clastic > Conglomerate (Tuffaceous)
Map references
Bureau of Economic Geology, 1992, Geologic Map of Texas: University of Texas at Austin, Virgil E. Barnes, project supervisor, Hartmann, B.M. and Scranton, D.F., cartography, scale 1:500,000
Unit references
Bureau of Economic Geology, 1982, Fort Stockton Sheet, Geologic Atlas of Texas, University of Texas at Austin, scale 1:250,000.
Bureau of Economic Geology, 1979, Emory Peak--Presidio Sheet, Geologic Atlas of Texas, University of Texas at Austin.
Counties Brewster - Jeff Davis - Presidio