Nestled between the San Andreas Mountains to the west and the Sacramento Mountains to the east lies the Tularosa Basin.
Today, Tularosa is an endorheic basin, which means no water outflows from its cupping contours via rivers or oceans. In these types of basins, water pools internally in swamps or lakes. Since the Tularosa Basin resides in New Mexico, you can guess it doesn’t contain classic wetlands. Sometimes endorheic basins only seasonally form internal lakes, as the water evaporates to achieve equilibrium, which we call playas. When these attributes align, we can observe the seemingly paradoxical desert basin.
The Tularosa Basin is notable for another reason, though. Thanks to a quirk in geological evolution, it’s home to one of the world’s unique wonders: White Sands.
Between 250-280 million years ago, the land of the Earth formed a mega-continent, known as Pangea. The part of the surface that is now the southwestern United States lay under ocean water. As the seas dissipated, they left a layer of calcium sulfate or gypsum. This mineral forms a few common substances, such as plaster, chalk, and drywall.
About 70 million years ago, tectonic collisions formed the major ranges of the region, including the Rockies. Locally, the San Andreas and the Sacramento mountains formed. Originally, the two spans were not separated, but about 30 million years ago they were ripped tectonically asunder. This action formed a massive bowl, the Tularosa Basin.
During the last Ice Age – between 12,000 and 24,000 years ago – rains arrived in the region. As the climate warmed and water poured onto the mountains, the gypsum, once on the bottom of an ocean but now lining peaks, started to run into the basin. The water and the minerals pooled in a body called Lake Otero.
When the Ice Age ended, the modern Chihuahuan Desert began to take shape. The sun worked hard on Lake Otero, sucking its waters to the sky. What remained were gypsum crystals called selenite, which line a portion of what was Lake Otero that we today call Alkali Flat.
Over the past 10,000 years, the power of the wind took over, eroding the selenite into tiny grains. The process also polishes the pieces, transforming them into a brilliant white color.
The winds typically push in a northeastern direction. As time and wind continue, the small, white grains congeal into dunes.
The result is the extraordinary White Sands National Park.
The tract of white sand dunes in New Mexico is over 275 square miles in area. Only three gypsum dune fields exist on the planet. White Sands is by far the largest of the three; another populates Guadalupe Mountains National Park, while the third is in Mexico. We think of sand as the glassy rocks that line seashores, but the “sand” portion of that material actually refers to the size and not the composition. Most sand is composed of quartz. The conditions to produce gypsum sand fields are rather rare and the geographical idiosyncrasies of the Tularosa Basin produced a singular marvel.
The 275 square miles are covered with approximately 30 feet of gypsum sand. Then, at the surface, the wind has whipped up dunes that rise as high as 60 feet! All the wonderful types of dunes emerge at White Sands, including dome dunes, transverse dunes, barchan dunes, and parabolic dunes.
The process that created the white sand continues today. Gone is Lake Otero, but water is not an alien there. Playas periodically fill with water, which allows the erosional cycle to persist. Where the waters pool today is called Lake Lucero.
Though the region rightly garners an arid reputation, life persists at White Sands because water is actually not missing!
Counterintuitively, the water table rests mere feet below the surface. Since the basin doesn’t naturally drain, the water that cannot evaporate has to go somewhere. And that somewhere is down.
This allows vegetation, particularly the yucca, to produce vast, hardy root systems in the sea of sand. Some of the flora can even “move” with the ever-changing dune waves. As sand covers a plant, spots previously too deep in the sand become prime real estate for new seeds. Many moths – up to 40 species – are endemic to White Sands, including the Yucca moths, which pollinate only yuccas. Species of plants and insects at White Sands have evolved as soulmates, their lives depending on each other.
Of course, where there is flora there is fauna.
More than 250 species of birds, 50 mammals, 30 reptiles, seven amphibians, and even a fish exist at White Sands. Many of them live underground and emerge mostly at night to avoid the harsh temperatures.
Many desert animals have evolved to blend into the oranges and browns that tend to dominate these climates. A few species have followed suit in White Sands, becoming lighter to camouflage themselves. The Apache pocket mouse, the bleached earless lizard, the sand-treader camel cricket, the sand wolf spider, and several moths have all become white over the millennia.
Though the United States military uses the greater Tularosa Basin as a missile range, White Sands National Park carved a fantastic wedge in which humans can frolic.
The park contains a variety of “trails,” from easy boardwalk sections that anyone can enjoy to the five-mile Alkali Flat trail that plunges into the heart of the dunes. Buoys mark the trail, as the shifting sands would erase any traditional path.
Because the sand is white, it actually is cooler than one might expect in a desert. This temperature allows the intrepid visitor to become a sledder! Vendors at the entrance peddle sleds, which allow people to pretend they’re on 60-foot snowhills.
It’s difficult to express the expanse of gypsum dunes at White Sands. The sand is something every human should view, walk through, and feel.
It’s a splendor meant to be drawn on during a ranger-guided sunset tour!
Further Reading and Exploration
White Sands National Park – Official Website
Geology of White Sands – National Park Service
WHITE SANDS NATIONAL PARK – Visit Las Cruces
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