Great trails explore White Sands’ geology

White Sands is the world's largest gypsum sand dune.
Photo courtesy White Sands NPS.

The world’s largest gypsum dunefield sits in southcentral New Mexico. At 275 square miles, about 4.5 billion short tons of white gypsum crystal make up the entire dunefield. White Sands National Park protects the southern half of the field. The dunes rise an average of 30 feet above the surface at White Sands, with the tallest dune about six-and-a-half stories high.

The sand dunes owe their creation to events from 251 million to 299 million years ago during the Permian. At the time, shallows seas covered this part of the world. When they receded, a seabed rich in gypsum was left behind. As the San Andres and Sacramento mountains rose, the gypsum was lifted to higher elevations. Rain dissolved the water-soluble gypsum, with rivers carrying the mineral down the mountains and depositing it in the basin below.

Fast-forward to the end of the last ice age, about 10,000 BC. Large lakes, streams and grasslands filled the Tularosa Basin between the two mountain ranges. As the ice sheets retreated, weather patterns shifted, causing the basin to warm and dry out. One waterbody, Lake Otero, evaporated and became the alkali flat while the grassland turned to desert.

Exposed selenite crystals on the flat eroded into gypsum grains between 8000 and 5000 BC. Prevailing winds then blew the grains eastward, forming dunes, which stabilized about 2000 BC.

Three great trails to explore White Sands’ geology are:
• Alkali Flat Trail
• Interdune Boardwalk
• Playa Trail