White Sands National Monument

White Sands National Park is an American national park located in the state of New Mexico and completely surrounded by the White Sands Missile Range. The park covers 145,762 acres in the Tularosa Basin, including the southern 41% of a 275 sq mi field of white sand dunes composed of gypsum crystals. This gypsum dunefield is the largest of its kind on Earth, with a depth of about 30 feet, dunes as tall as 60 feet, and about 4.5 billion short tons of gypsum sand.

Approximately 12,000 years ago, the land within the Tularosa Basin featured large lakes, streams, grasslands, and Ice Age mammals. As the climate warmed, rain and snowmelt dissolved gypsum from the surrounding mountains and carried it into the basin. Further warming and drying caused the lakes to evaporate and form selenite crystals.

Source: Wikipedia