The White Sands National Monument is a U.S. National Monument located about 25 km (16 mi) southwest of Alamogordo in western Otero County and northeastern Dona Ana County in the state of New Mexico, at an elevation of 4235 feet (1291 m). The area is in the mountain-ringed Tularosa Basin valley area and comprises the southern part of a 710-km² (275-mi²) field of white sand dunes composed of gypsum crystals.