The Largest Pure Gypsum Dune Field in the World
Gypsum, (Hydrous Calcium Sulfate CaS04. H20)
Gypsum is rarely found in the form of sand because it is water-soluble
Gypsum is one of the most common minerals on earth. 'Yeso' is Spanish for gypsum
Gypsum is used to make cements and plasters especially Plaster of Paris.

On 18 January 1933, President Herbert Hoover created the White Sands National Monument.

Gypsum does not readily convert the sun's energy so even in the hottest summer months
 the dunes can be walked upon safely with bare feet, unlike dunes made of quartz-based sand crystals.

White Sands National Monument lies adjacent to the the largest military installation in the United States,
White Sands Missile Range  (3,200 square miles)

The monument ranges in elevation in the Tularosa Basin from 3890' to 4116' above sea level
 and is 275 square miles of desert.

The Unique set of circumstances that led to the creation of White Sands....
   The Dunes originated in the western portion of the monument when the Tularosa Basin was filled with an enormous Ephemeral lake, called Otero, that covered this area 250 million years ago (Ephemeral: short lived). Then gypsum-bearing marine deposits were uplifted into a giant dome 70 million years ago when the Rocky Mountains were formed. Beginning 10 million years ago, the center of this dome began to collapse and create the Tularosa Basin. The remaining sides of the original dome formation now form the San Andres and Sacramento mountain ranges that ring the basin. Rain and snow that fall in the surrounding mountains dissolve marine rocks (gypsum is a breakdown of selenite crystals) and carry it into the Tularosa Basin where it was trapped because no rivers drain from the basin or from Lake Lucero. Deposited at the bottom of a shallow sea it eventually evaporates into a salt crust of tiny gypsum crystals that the wind sweeps away. There are several types of dunes that form at white sands. Dome dunes are low mounds of sand that move up to 30 feet per year downwind from Lake Lucero. Barchan dunes, or transverse dunes, are crescent-shaped dunes formed in areas with strong winds but have a limited supply of sand. Transverse dunes join together with barchan dunes into long ridges of sand. Parabolic dunes are on the dune field edges where plants anchor the arms of barchans and invert their shape. Dunes are subject to different forms and sizes based on their interaction with the wind. Most kinds of dune are longer on the windward side where the sand is pushed up the dune, and a shorter "slip face (dune's concave side) in the lee of the wind, also none as a ridge or razorback. The "valley" or trough between dunes is called a slack. A "dune field" is an area covered by extensive sand dunes. Large dune fields are known as ergs.