Sierra Madera

The Sierra Madera crater is a complex impact crater (astrobleme) in southwestern Pecos County, Texas, United States. The impact structure spans approximately 8 mi (13 km) in diameter and is centered 20 mi (30 km) south of Fort Stockton, roughly equidistant from Mexico and New Mexico and near the northeastern end of the Glass Mountains. The central peak of the rebound structure of the impact crater rises 793 ft (242 m) above the surrounding land. The peak is visible from U.S. Highway 385 between Fort Stockton, Texas and Marathon, Texas. The Sierra Madera crater is located on private property on the La Escalera Ranch. The crater is mostly eroded but remains well exposed. At the center of the crater are the hilly remains of the central peak produced by the impact. Known as Sierra Madera or Madera Mountain, the uplift rises 4,593 ft (1,400 m) above sea level. The peak occupies most of the crater and is its most prominent feature, spanning about 5 mi (8 km) across. Strongly folded and faulted carbonate and siliciclastic rock layers from the upper Paleozoic to Cretaceous comprise the central structure, along with breccia fragments spanning as much as several meters across. The oldest Permian rocks in the structure lie 3,900 ft (1,200 m) above their typical position. The strata folded in the central uplift provide an indication of the impact's age. An alluvium-filled depression up to 1 mi (1.6 km) wide surrounds the central uplift, outlined by an outer concentric crater rim about 0.5 mi (0.80 km) wide. The crater rim consists of low hills that climb subtly above the surrounding land. The first geological map of the Sierra Madera was published in 1930. The central peak was initially interpreted as a cryptovolcanic structure. However, no igneous rocks were detected within 13,000 ft (4,000 m) of the surface.