White Sands in the Tularosa Basin. White Sands National Monument, New Mexico, USA. The glistening dunes of White Sands in the Tularosa Basin are not sand, but fine gypsum, deposited on an ancient seabed 250 million years ago. Gypsum, a form of calcium sulfate, is water soluble and washes away. But geological forces here created a basin with no outlet. Against the background of the snow-capped Sierra Blanca Peak (11.973ft., 3.649m). Photographed in late March.