In Permian basin Tascotal Formation mapped: a) alone in the Sierra Vieja area, Presidio Co, west TX, where it is shown above Mitchell Mesa Welded Tuff of Vieja Group on the Correlation of Map Units; and b) as a formation of Buck Hill Group in the southeastern part of mapped area, Presidio Co--Buck Hill consists of (ascending): Duff and Pruett Formations (undivided) and Duff Formation, Mitchell Mesa Welded Tuff, and Tascotal Formation. Shown below Petan Basalt in both areas. Upper part of Tascotal: sandstone, tuffaceous sandstone, and conglomerate; sandstone medium to coarse grained with lenses, beds, and channel fillings of pebble to cobble conglomerate, mostly limestone, some igneous rocks and chert, about half of interval is tuff and sandy tuff. Lower part: tuff, flaggy, slightly calcareous, light colored; some interbeds of tuffaceous fine-grained sandstone. Thickness 710 ft. [Author states that correlation of volcanic rocks from area to area on Marfa sheet is uncertain--little attempt is made to correlate between areas. The rocks are described by area.] Of Oligocene age. Geologic map.

Source: GNU records (USGS DDS-6; Denver GNULEX).