White Sands National Monument is a United States national monument located in the state of New Mexico on Route 70 approximately 54 miles (87 km) northeast of Las Cruces and 16 miles (26 km) southwest of Alamogordo in western Otero County and northeastern Doña Ana County. The monument is situated at an elevation of 4,235 feet (1,291 m) in the mountain-ringed Tularosa Basin and comprises the southern part of a 275 sq mi (710 km²) field of white sand dunes composed of gypsum crystals. The gypsum dune field is the largest of its kind on Earth.