Geologic map of southern Quitman Mountains and vicinity, Hudspeth County, Texas

The Quitman Mountains are part of a narrow mountain range that extends southeastward from near Sierra Blanca, Texas (85 miles southeast of El Paso, Texas), into northern Mexico. The range is typical of many desert mountains of the southwestern United States in that it projects abruptly above the breached bolsons that border it. Thus, the Quitman Mountains stand in stark contrast topographically and geologically to the Hueco Bolson on the west and the Red Light Bolson on the east. Quitman Gap (also called Quitman Canyon, Quitman Pass, and Can de los Lamentos) divides the range into northern and southern parts. The northern Quitmans, composed of Tertiary intrusive and volcanic rocks with intensely folded Cretaceous rocks exposed around the periphery of the igneous mass, extend about 10 miles north-northwest from Quitman Gap to Interstate Highway 10. The southern Quitman Mountains, composed primarily of intensely folded and thrust-faulted Cretaceous rocks, extend from Quitman Gap south-southeast to the Rio Grande (a distance of about 25 miles). The elevation of the range gradually diminishes southward from about 6,600 feet above sea level in the northern part to slightly less than 4,000 feet above sea level near the Rio Grande. The maximum local difference in elevation is about 2,000 feet. The highlands of the area studied are horsts flanked by grabens that are partly filled with sediment eroded from the mountains to form intermontane basins. The block faulting that created the horst and graben system followed the igneous activity and was superimposed on the earlier Laramide folds, thrust faults, and strike-slip faults characteristic of the Chihuahua tectonic belt. The Cretaceous rocks exposed in the southern Quitman Mountains consist of about 14,000 feet of marine shale, sandstone, and limestone, and nonmarine sandstone and shale. The lower 3,000 to 4,000 feet of the sequence are nonmarine rocks. Volcanic rocks overlie truncated folds in the Cretaceous sequence and consist mostly of tuffs, welded tuffs, and andesite. The bolsons are filled by relatively undisturbed Tertiary and Quaternary sediments that were deposited as interbedded conglomerates and fine-grained lacustrine-playa deposits.