|Geologic age||preCambrian (Proterozoic); Grenville Series|
Igneous > Volcanic > Felsic-volcanic > Rhyolite (Stock or pipe)porphyritic, well-defined layering, massive, dk. red or black, rded qtzite pebbles near base, thickness 1.400 ft max.
|Comments||Franklin Mtns.: rhyolite is porphyritic, feldspar and quartz phenocrysts, widely spaced but well-defined layering, massive, dark red to black, rounded quartzite pebble near base, thickness 1,400 ft max. Pump Station Hills: rhyolite porphyry, phenocrysts of pink feldspar up to 1 cm across and clear, glassy quartz, aphanitic groundmass, massive, maroon to dark red; base covered. (from Geol. Atlas of Texas, Van Horn-El Paso Sheet, 1968)|
Bureau of Economic Geology, 1968, Van Horn-El Paso Sheet, Geologic Atlas of Texas: Bureau of Economic Geology, The University of Texas at Austin, scale 1:250,000.
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.
|Counties||El Paso - Hudspeth|