White Sands NM

White Sands National Monument is located at the northern end of the Chihuahuan Desert in the Tularosa Basin of southern New Mexico. About 250 million years ago, this area was covered by a shallow sea, from which gypsum was deposited on the sea floor. These deposits eventually were buried under other materials that later turned to stone. Millions of years later, the sea withdrew, and the rocks that it left behind arched upward into what is called an anticline. The basin was formed when the central portion of the anticline collapsed. The western and eastern ridges that remained are now the San Andres and Sacramento mountains, respectively. This collapse exposed the gypsum deposits in the San Andres Mountains, which are periodically dissolved in water and carried to a playa lake within the closed Tularosa Basin (it has no outlet to the sea). As the playa lake periodically dries, gypsum crystals are formed on its bed, and these are broken down into grain-sized particles that are carried by the wind to form the dunes.

Class Walking on the Dunes, White Sands National Monument, New Mexico
Photograph by Mark Eberle, March 1999

The dunes are constantly moving due to the strong winds that carry the grains of gypsum. Because the dunes move, plants have had to adapt accordingly. Soaptree yucca can extend its stems up to 30 cm per year to keep its leaves above the sand. Other plants use their roots to anchor pedestals of sand and continue to grow after the dune moves forward (photograph below left). Some animals have evolved lighter coloration to help camouflage them on the surrounding sand (photograph below right), which would not be advantageous in the black lava beds of the Valley of Fires just to the north in the Tularosa Basin (described on the webpage "Volcanic Features").

Plant Dune Pedestal and Cricket, White Sands National Monument, New Mexico
Photographs by Mark Eberle, March 1999, and William Stark, March 2000

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