GLASS MOUNTAINS. The Glass Mountains (at 30°26' N, 103°07' W) extend from Cathedral Mountain in northern Brewster County to Monument Draw in southern Pecos County. U.S. Highway 385 runs through the eastern portion of the range. The Glass Mountains' highest elevations reach over 5,700 feet above sea level and are in the range's western reaches, north of Marathon in Brewster County. The underground water source of Comanche Springs in Fort Stockton originates in the Glass Mountains. The area terrain varies from steeply sloped to flat, with local deep and dense dissection. Soils in the vicinity are generally shallow and stony and support oak, juniper, and some mesquite.