TRAP MOUNTAIN. Trap Mountain is just south of the Castolon road near the Mule Ears Overlook in Big Bend National Park, six miles east-northeast of Castolon in southern Brewster County (at 29°10' N, 103°26' W). It stands isolated in rugged desert terrain at the southwest margin of the Chisos range. Its steep sides rise sharply to a peak some 1,300 feet above the surrounding desert floor, and at its highest point it reaches 4,125 feet above sea level. The name of the mountain may come from the dark appearance of the rocks in this and other members of the Chisos range, particularly the ones composed mainly of basalt. (The term trap used to be applied to dark, fine-grained, volcanic rock.) The area is relatively sparsely vegetated; the most common plants include shrubs such as creosote bush and ocotillo and semisucculents such as lechuguilla and yucca. The desert scrub community displaced what was once predominantly a semiarid grassland ecosystem in this region as the latter deteriorated under the burden of overgrazing by the commercial livestock industry in the years before the area came under National Park Service protection.