Adobe Walls Mountain is located twelve miles north of Study Butte, Texas, and two miles east of State Highway 118 in southwestern Brewster County (at 29°29' N, 103°30' W). It rises on its northern side in a long slope from the desert floor and falls off in sheer cliffs of bare rock some 500 feet high on its southern face. The elevation of its highest point is 4,510 feet above sea level. Vegetation in the area consists primarily of Chihuahuan Desert scrub, characterized by various shrubs and semisucculents that have partially replaced grassland as a result of overgrazing. Adobe Walls Mountain marks the northern edge of the historic Terlingua quicksilver district (see MERCURY MINING). The mountain is named for the incomplete adobe walls that once surrounded the main ranchhouse of the G4 Ranch.