Pruett Formation mapped together with Duff Tuff in the Cuesta del Burro area in the southeastern part of the mapped area, Presidio Co, west TX in the Permian basin. Assigned to Buck Hill Group. The Duff and Pruett (undivided) consists of rhyolitic tuff and intercalated tuffaceous clay, silt, sandstone, and conglomerate, moderate to well indurated, white, gray, red, and yellow. Thickness of Duff Tuff and Pruett Formation (undivided) is as much as 1,500 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.] Is of Oligocene age. Geologic map.

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