Desert Places: Cuatro Cienegas Reserve and White Sands National Monument
by Russell Brown

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Both White Sands National Monument in New Mexico and Cuatro Cienegas Reserve in Coahuila offer unexpected vistas and natural resources that that reward the visitor who takes the time to make more than a cursory visit.

Gypsum dunes require that there is a method for the gypsum to be transported by water and yet then be in a sufficiently arid environment that the gypsum is not dissolved and washed away. The two seem mutually exclusive and that is why large surface deposits of gypsum are rare.

At White Sands National Monument, gypsum is dissolved from Permian deposits near the tops of local mountains and carried into the Tularosa basin, where the water is evaporated and leaves the gypsum as an evaporite deposit on the basin floor. The crystallized gypsum, or Selenite, then erodes down to sand and is blown by the prevailing winds into the world's largest gypsum dune field. The vast vistas of pure white gypsum dunes are a welcome surprise to any visitor taking the time to walk to the top of a dune near the heart of the sands. While this desert within a desert may seem so inimical to life that nothing could survive for long, visitors coming to the park in the early morning will find the sand covered with tracks left by the nocturnal residents of the dune field.

At Cuatro Cienegas, the mechanism for gypsum deposition may be more cryptic. One of the more prevalent explanations is that the gypsum is actually formed on the valley floor. The Cuatro Cienegas valley is underlain by a vast hydrologic system that may continue all the way to Texas in the United States. The surrounding mountains and substrate are sedimentary with a large limestone component and isolated igneous deposits. The prevailing theory is that the gypsum is formed from calcium in the ground water and sulfur that is leached out of the igneous deposits. As the water evaporates from local pools. The calcium and sulfate ions combine to form gypsum, which then blows into dune fields, the largest of which covers eight square miles. Until recently, this gypsum was being mined but now that mining has ceased we hope that this field will become even larger and more pristine.

The same system that allows the gypsum to form at Cuatro Cienegas also presents a unique environment of semi isolated pools and endemic wildlife, such as stromatelites, which are exceedingly rare in the world and totally unexpected in a desert setting.

We hope that visitors can take the time to visit and appreciate these two unique but related environments and that you will spend some time in advance looking up these areas on the internet so that your visit will be even more rewarding.

Russell Brown works for the National Park Service at White Sands National Monument in New Mexico. He can be reached via email: rbrown@zianet.com.

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