White Sands National Monument is an area of the Tularosa Basin in southern New Mexico that a 275 squaremile field of white sand with gypsum crystals. Gypsum in the form of sand is rare because it is water soluble and is usually dissolved by water and into the sea. However, because the Tularosa Basin has no outlet to the sea, the gypsum trapped in the sand and sinks to the ground or forms pools that dry out, the gypsum in a crystalline form called selenite on the . Because the gypsum in the sand does not trap heat, visitors can walk on the surface burning their feet.