Landscape Evolution of Eagle Flat and Red Light Basins, Chihuahuan Desert, South-Central Trans-Pecos Texas

This report documents the development of the landscape near the site proposed for the Texas low-level radioactive waste repository, located in southern Hudspeth County, Texas. It documents the geomorphic, depositional, and erosional features in the area. The Texas Legislature designated an approximately 400 square mile (1,035 square kilometer) area as the Eagle Flat Study Area, within which the site was to be selected. The study area consists of six U.S. Geological Survey 7.5-minute topographic quadrangles between the towns of Sierra Blanca and Van Horn, Texas. The six-quadrangle Eagle Flat Study Area contains a large part of Eagle Flat Basin and a smaller area in Red Light Draw.

The Eagle Flat Study Area contains parts of the Belson and Sacramento subsections of the Mexican Highlands section in the Basin and Range physiographic province. The Belson subsection is characterized by broad, internally drained alluvial basins, interrupted by rugged, discontinuous fault-block mountains. The mountains are composed of Cretaceous and Permian carbonate rocks with scattered areas of Tertiary intrusives and volcanics, older Paleozoic shata, and Precambrian metamorphic rocks. In the Belson subsection, the uplands make up about one-fifth of the area, whereas uplands make up 27 percent of the entire Eagle Flat Study Area. The Eagle Flat and Red Light Draw Basins, in the Belson subsection, are floored by Pliocene and Pleistocene alluvial sands and muds. The Sacramento subsection is represented by the Diablo Plateau in the northern part of the study area. This plateau is an upland area of Cretaceous hills separated by broad alluvial valleys with thin sedimentary cover.

The Eagle Flat Study Area contains the four geomorphic regions: the mountainous region, the upland region, the basin floor, and the Sacramento Plateau.