page_title: White Sands National Park
section_title: Geology
hierarchical_section_title: White Sands National Park / Geology
caption_attribution_description: English: Gypsum sand from White Sands National Monument, New Mexico. Photograph by Mark A. Wilson (Department of Geology, The College of Wooster).
context_page_description: White Sands National Park is an American national park located in the state of New Mexico on U.S. Route 70 approximately 15 miles southwest of Alamogordo and 52 miles northeast of Las Cruces, in western Otero County and northeastern Doña Ana County. The park is situated at an average elevation of about 4,000 feet in the Tularosa Basin and comprises the southern part of a 275 sq mi field of white sand dunes composed of gypsum crystals. The gypsum dunefield is the largest of its kind on Earth.
  The park was originally designated White Sands National Monument on January 18, 1933 by President Herbert Hoover, and redesignated as a national park when Congress passed the 2020 National Defense Authorization Act on December 20, 2019. The park encompasses 145,762 acres protecting 115 sq mi of the dunefield, about 41%, while the remaining 160 sq mi are located to the north within White Sands Missile Range. The depth of gypsum sand across the entire field is about 30 feet below the interdunal surface, while the tallest dunes are about 60 feet high. About 4.5 billion short tons of gypsum sand fill the dunefield, which formed about 7,000–10,000 years ago.
context_section_description: During the Permian Period, shallow seas covered the area that today forms White Sands National Park. The seas left behind gypsum (calcium sulfate), and subsequent tectonic activity lifted areas of the gypsum-rich seabed to form part of the San Andres and Sacramento Mountains. Over time, rain dissolved the water-soluble gypsum in the mountains, and rivers carried it to the Tularosa Basin, which has no outlet to the sea. The trapped water sank into the ground or formed shallow pools that subsequently dried out, leaving the gypsum on the surface in a crystalline form called selenite. Groundwater that flows out of the Tularosa Basin flows south into the Hueco Basin. 
  During the last ice age, a 1,600-square-mile (4,144 km²) body of water named Lake Otero covered much of the basin. When it dried out, a large flat area of selenite crystals remained, which is named the Alkali Flat.
  Lake Lucero is a dry lakebed in the southwest corner of the park, at one of the lowest points in the basin. Rain and snowmelt from the surrounding mountains and upwelling from deep groundwater within the basin periodically fill Lake Lucero with water containing dissolved gypsum. When filled, the lake covers about 10 square miles (26 km²) at a depth of 2–3 ft (0.61–0.91 m). As the water evaporates, small selenite crystals about 1 inch (2.5 cm) in diameter form on the surface of the lake. Most of the crystal formation occurs when large floods concentrate the mineralized water every ten to fourteen years. Wind and water break down the crystals into progressively smaller particles until they are fine grains of white gypsum sand.
  The ground in the Alkali Flat and along Lake Lucero's shore is also covered with selenite crystals that measure up to 3 ft (0.9 m) long. Weathering and erosion eventually break the crystals into sand-size grains that are carried away by the prevailing winds from the southwest, forming the white dunes. The dunes constantly change shape and slowly move downwind. Since gypsum is water-soluble, the sand that composes the dunes may dissolve and cement together after rain, forming a layer of sand that is more solid, which increases the wind resistance of the dunes.
  The increased resistance does not prevent dunes from quickly covering the plants in their path. Some species of plants can grow fast enough to avoid being buried by the dunes, while others utilize survival strategies such as the formation of a hardened pedestal around their roots to stabilize the plant amid the moving dunes.
  White Sands contains various forms of dunes. Dome dunes are found along the southwest margins of the field, transverse and barchan dunes in the center of the field, and parabolic dunes along the northern, southern, and northeastern margins. Scientists have surveyed a 9.3-mile (15 km) long strip of dunes with lasers; installed shallow water wells across the dunefield; looked at the chemistry and age of the water below the dunes; measured hundreds of thousands of individual sand grains from across the dunes; and used satellites to see temperature and moisture changes throughout the year.
  Toward the western side of the dunefield, the dunes are more than 50 ft (15 m) tall, and they become progressively smaller toward the eastern edge, until they come to an abrupt stop at the eastern boundary. Throughout the dunes, water is only a few feet (a meter) from the surface and very salty, but toward the western edge of the dunefield, the water is older and even saltier. The depth to groundwater also decreases from 5 ft (1.5 m) below the surface on the eastern end to only 1–2 ft (0.3–0.6 m) on the western end of the dunefield. The dunes at the western end have very little vegetation and move very quickly, while the dunes on the eastern end move very slowly and are very vegetated. Toward the western edge, the sand grains become larger and have all different shapes, while at the eastern edge they are all very small and round. The dunefield is much cooler and wetter than the surrounding hot, dry desert soils based on satellites images. Scientists have discovered what app
caption: Gypsum sand
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