The West Texas and Trans-Pecos region is perhaps the most complex of all the regions. It inhabits the extreme western part of the state eastward mostly to the Pecos River. Elevations range from 2,500 feet to more than 8,749 feet at Guadalupe Peak. This is a region of varied habitats and flora, varying from the desert valleys and plateaus to wooded mountain slopes. Even the mountain ranges vary tremendously in the environments they offer for plant and animal life. These mountain ranges are characterized by volcanic rocks, others by limestone. Over most of the area average annual rainfall is less than 12 inches but varies greatly from year to year and from lower to higher elevations. July and August are usually the higher rainfall months. Mountain outwash materials have formed the soils of the Trans-Pecos. Due to the diversity of soils and elevations in the region, many species of vegetation exist. The chief plant communities are creosote-tarbush desert scrub, desert grassland, yucca and juniper savannahs, and mountain forests of pinon pine and oak. The Sand Hills area consists of shin oak and mesquite on wind-blown dunes. Flat-topped mesas and plateaus are intersected by steep-walled canyons and dry washes that comprise the Stockton Plateau. Soils with high salt content and gypsum dunes are typical of the Salt Basin area. The Desert Scrub sub region is an area of low rainfall and rapid drainage. Creosote bush flats with yucca, lechuguilla, and various small-leafed plants are common. The Desert Grassland area occurs in the central part of the region and is characterized by deeper soils with high clay content. Finally, the Mountain Ranges have higher rainfall and woody vegetation such as junipers, oaks, pinon pine, ponderosa pine, and Douglas fir. Ranching is the primary industry in the Trans-Pecos region.
Major Rivers: Devils River, Pecos River, Rio Grande
Major Aquifer: Edwards, Pecos Valley, Hueco-Mesilla Bolsons