El Capitan () is a peak in Culberson County, Texas, located within Guadalupe Mountains National Park. The 10th-highest peak in Texas at 8,085 ft (2,464 m), El Capitan is part of the Guadalupe Mountains, an exposed portion of a Permian period reef uplifted and exposed by tectonic activity during the late Cretaceous period. The southern terminus of the Guadalupe Mountains, El Capitan looms over U.S. 62/180, where its imposing height and stark outline have made it one of the iconic images of the Trans-Pecos to generations of travelers. Geology El Capitan is the southernmost peak of the Guadalupe escarpment, an ancient limestone reef that forms the present-day Guadalupe Mountains. These mountains are an exposed portion of the Capitan Reef Barrier, a 350-mile long reef constructed primarily from calcareous sponges, encrusting algae, such as stromatolites, and lime-rich mud directly from the ocean. This reef surrounded much of the Delaware Sea, an inland ocean that covered parts of modern southern New Mexico and Trans-Pecos Texas in the Permian period (about 290 million years ago). Near the end of the late Permian period, in the Ochoan epoch, the outlet that allowed sea water to enter the inland waters began to silt over, occasionally closing the inland sea from its source. Mineral-rich and cut off from replenishment, the inland sea began to evaporate into layers of alternating gray anhydrite/gypsum, brown calcite, and halite, which formed the Castile Formation. As salt concentrations increased, laminated halite, anhydrite, sylvite, and polyhalite formed the Salado Formation, which eventually covered and grew beyond the lower Castile Formation. By the end of the Ochoan, these deposits had filled the roughly 1,800-ft-deep basin and covered the reef with dry land. Red silt and sand deposited by rivers crossing these new lands eventually formed the dolomitic Rustler Formation, and the Dewey Lake Formation, burying the reef even deeper. The Capitan Reef stayed buried for over 150 million years, until the late Cretaceous period of the Mesozoic era (80 million years ago), when tectonic activity associated with the Laramide Orogeny caused a significant uplift in the area and created a major fault line, the Border Fault, in the area west of the Delaware Basin. Exposing the Guadalupe Mountains area of the reef, the impact of this tectonic event can be clearly seen in the difference in height between the towering El Capitan and the adjacent salt flat graben, vertically driven 1,000 feet apart