Sierra del Caballo Muerto is a segment or subrange of the Sierra del Carmen in southeastern Brewster County and northern Coahuila, Mexico (midpoint at 29°22' N, 102°56' W). The Sierra del Carmen is the northernmost extension of the Sierra Madre Occidental, which enters Texas out of Mexico. The Sierra del Carmen consists of a series of northwestward-oriented high ridges, of which the Sierra del Caballo Muerto is the longest and most central ridge. Sierra del Caballo Muerto means "Dead Horse Range" and Dead Horse Mountains is, in fact, the name most commonly applied by residents of the region to the entire del Carmen range on the Texas side of the river. The name has several possible origins: the most popular version cites an incident in 1881 in which a detachment of Texas Rangers under Capt. Charles L. Neville captured a number of Indian ponies in a canyon in those mountains and slaughtered them on the spot rather than permit their owners to recover them. A second story claims that two cowboys in the 1880s discovered a remuda of horses trapped in a canyon there. The cowboys, despite repeated attempts, were unable to rescue the horses and were instead forced to watch for a number of weeks as the horses starved to death. Alternatively, several sources claim that government surveyor Arthur A. Stiles, who conducted a number of "naming meetings" with local residents in 1903 to designate regional place names, coined the name Caballo Muerto because his favorite saddle horse fell to its death from a high cliff in those mountains. It is also possible that the name originated with the eighteenth-century Spanish explorers who traversed the region. The Sierra del Caballo Muerto consists of a series of fault blocks tilted toward the west, with the faults controlling the escarpment positions. The Caballo Muerto ridge is thirty miles long and is well over 4,000 feet above sea level for most of its length, with high points near the middle of the range of 5,854 feet at Sue Peak and 5,107 feet at Stuarts Peak. At its northwest extremity the Sierra del Caballo Muerto gradually drops to an elevation of about 3,000 feet before it ends in Dagger Flat ten miles southeast of the Persimmon Gap Ranger Station in Big Bend National Park. At its southeastern end on the Rio Grande the range drops abruptly as much as a thousand feet or more to form the north wall of Boquillas Canyon. The harsh, rugged slopes of the Dead Horse Mountains are covered for the most part by characteristic Chihuahuan desert scrub. The range is also cut, however, by many beautifully sculpted dry washes and shut-ins, where more riparian-like vegetation, such as desert willows and honey mesquite, may be found. The animal and bird life in the range is also typical of the Chihuahuan Desert, although some sightings of particular note have been made there. As late as the 1930s black bear still lived in the Dead Horse Mountains, and the only record of a coati in the Trans-Pecos was made there in 1939.