From Wikipedia:
Rising from the heart of the Tularosa Basin is one of the world's great natural wonders - the glistening white sands of New Mexico. Here, great wave-like dunes of gypsum sand have engulfed 275 square miles of desert and created the world's largest gypsum dune field.
White Sands National Monument preserves a major portion of this unique dune field, along with the plants and animals that have successfully adapted to this constantly changing environment.
The desert lies under the scorching sun of Tularosa Basin New Mexico, its white sands gleaming like freshly fallen snow. These powdery grains of sand are not composed of quartz, unlike most desert sands, but of soft, chalky
gypsum, or
calcium sulfate. Also, unlike other desert sands, they are cool to the touch, due to the high rate of evaporation of surface moisture and also to the fact that the sands reflect, rather than absorb, the sun's rays.
It is the world's largest surface deposit of gypsum, the mineral from which plaster of Paris is made.
Gypsum is one of the most common mineral compounds found on Earth but is rarely seen on the surface, as it dissolves easily in water. The origins ofthis amazing 'desert' dates back to around 100 million years ago, during which it was covered by a shallow sea. As its waters gradually receded, salt water lakes were left behind, which eventually evaporated in the sun. In addition to salt, gypsum was also laid down in thick deposits on the old seabed.
The Sacramento and San Andreas mountain ranges, with the Tularosa Basin between them, started taking shape 65 million years ago. Giant upheavals in the Earth's crust folded and crumpled the land and the gypsum deposits, thrusting them high into the air.
Constant rainfall and meltwater coming from the mountains caused the gypsum to leach out and concentrated solutions were washed down the mountainsides. The gypsum solution accumulated in Lake Lucero, the lowest part of the Tularosa Basin. Water in the lake does not have any means of escaping except by evaporation, which leaves behind thin layers of crystalised gypsum, or
selenite. Weathering then reduces these crystals to fine, sandy grains. South-westerly winds carry the grains farther up the basin, and the grains pile in steep dunes that are often as high as 15 m (50ft). The winds carve more dunes and, at the same time, carry small amounts of the gypsum grains by distances of up to 9 m (30ft) a year.
This constant movement of the sands, added with their alkaline nature and the little amount of rainfall makes it difficult for plants to grow here.
