This report describes preliminary results of an ongoing study of the volcanic stratigraphy, caldera activity, and known and potential mineralization of the Chinati Mountains area of Trans-Pecos Texas. Many ore deposits are spatially associated with calderas and other volcanic centers.

Geologic map that depicts the surface geology of parts of Presidio, Brewster, and Terrell Counties, Texas. The 14-page booklet indicates geologic formations, abbreviations, and ages.

Geologic map that depicts surface geology of parts of Hudspeth, Culberson, Jeff Davis, and Presidio Counties, Texas. The 12-page explanatory booklet indicates geologic formations, abbreviations, and ages.

Hot springs and wells in West Texas and adjacent Mexico are manifestations of active convective geothermal systems concentrated in a zone along the Rio Grande between the Quitman Mountains and Big Bend National Park.

The West Chinati stock, well exposed in San Antonio Canyon and immediately westward on slopes of the southwestern part of the Chinati Mountains, Presidio County, Texas, is a large stocklike body of porphyritic hornblende granite cut by numerous dikes and irregular-shaped plutons of rhyolite, rhyo

Mountain-bounded basins or bolsons are the most important aquifer systems throughout most of southwestern and western United States and northern Mexico.

Tertiary rocks, including sandstone, conglomerate, shale, pyroclastics, tuff, and lava, are preserved in Big Bend National Park and in a much larger area to the west and northwest. Some of the rocks have distinctive characteristics that enable recognition by their lithology.