Included within this area is the Van Horn uplift of southern Hudspeth and Culberson counties, the Solitario uplift of southern Presidio and Brewster counties, and the Marathon uplift of northeast Brewster County. This region also includes the Big Bend area of Texas, a part of which has been set aside as a National Park where many interesting and important geological features may be seen.
The Trans-Pecos region is one of rugged [topography] with elevations as high as 8,700 feet, at Guadalupe Peak in the Guadalupe Mountains of northern Culberson County, and as low as 1,500 feet, in the Rio Grande valley.
Numerous invertebrate fossils occur in the [Cretaceous] limestones and shales of the Trans-Pecos region and in the [Paleozoic] rocks of the Marathon uplift. The Gaptank [formation] of [Pennsylvanian] age and the [Permian] [reef] limestones of the Glass Mountains are especially [fossiliferous]. In addition, many [vertebrate] fossils have been collected in Trans-Pecos Texas, particularly in and around Big Bend National Park.
TEXAS PLAINS
The plains of Texas are broad expanses of country with very little surface relief. Most of the plains support grasses and some have wooded areas, particularly along stream valleys.
The plains of the northwestern part of the State have been subdivided as follows.
High Plains
This area ([Pl. 9]), often called “the caprock,” is an elevated plateau which rises above the rolling plains which surround it. The High Plains are bounded by the Pecos River valley on the south, southeast, and west and by the North-Central Plains on the east.
The surface of the High Plains is very flat and characterized by a sparse cover of grasses and few trees. The surface strata consist largely of unconsolidated deposits of sands and gravels of [Quaternary] and [Tertiary] age, with remnants of Lower [Cretaceous] limestones along the southern margin. The rocks of the High Plains are mostly unfossiliferous, but mammalian remains have been found at several localities.
Plate 9
Physiographic map of Texas.