Which National Park Service park contains Earth’s largest gypsum sand dune field?

White Sands National Park contains Earth’s largest gypsum sand dune field.

The park lies in New Mexico’s Tularosa Basin and protects the southern portion of a vast field made from gypsum crystals. Gypsum usually dissolves in water, so large gypsum dunes are unusual. At White Sands, dissolved gypsum moved into a basin with no outlet, where evaporation left selenite crystals that wind gradually broke into sand.

The dune field covers roughly 275 square miles in total, while the park protects its southern section. Some dunes rise about 60 feet, and the deposits contain an estimated 4.5 billion short tons of gypsum sand. The dunes continue to shift as wind transports the pale grains across the basin.

President Herbert Hoover proclaimed White Sands National Monument on January 18, 1933. Congress redesignated it as a national park in 2019, making the modern name different from the historic monument name.