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East Potrillo Mountains
The East Potrillo Mountains are a mountain range in south central Doña Ana County, New Mexico. They are located approximately 25 miles (40 km) west of El Paso, Texas, 30 miles (50 km) southwest of Las Cruces, New Mexico, and 30 miles east of Columbus, New Mexico. The southern tip of the range is less than 5 miles (8 km) from the Mexican border. The mountains and most of the surrounding acreage are located on land owned by the Bureau of Land Management. Access to the general vicinity is through New Mexico State Road 9, and several unpaved county roads.
==Geology==
The East Potrillos can be generally described as an uplifted west-tilted fault-block. The mountains are located near the western margin of the Rio Grande Rift, a major structure that stretches from the vicinity of Leadville, Colorado, through central New Mexico, and into the Mexican state of Chihuahua. In southern New Mexico, several large basins are associated with the rift, including the Mimbres basin to the west of the Potrillos, and the Mesilla basin to the east. A large intra-rift horst lies between those two basins, and the range is situated on the horst. The uplifting of the Potrillos, together with the subsidence of nearby grabens, occurred in the late Tertiary. The eastern boundary of the horst is the active Robledo fault, which has created a scarp on the eastern side of the range.
The basal rocks in the range are sedimentary, and consist of limestone, dolomites, and silty beds of Middle Permian age. The thickness of these beds is approximately 950 feet (300 m). Disconformably above these beds are layers of Lower Cretaceous limestone, siltstone, sandstone, and conglomerate. These rocks are about 1,800 feet (570 m) in thickness on the northern part of the range, but thin to the south. These Cretaceous rocks are correlative with the Hell-to-Finish Formation (Aptian age) and the U-Bar Formation (late Aptian to middle Albian) found in other parts of southwestern New Mexico. Quaternary deposits include alluvial fans and wind-blown sands.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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