We ended the day by visiting White Sands National Monument. Here is an eerie landscape of enormous white sand dunes that seems more appropriate in a beach setting. Surrounding the monument is the White Sands Missile Range, the largest U.S. military installation, which had a significant history during World War II and the space program. It was here at the Trinity site where the first atomic bomb was detonated. The monument is actually a part of the missile range and is subject to closure when military tests are being conducted.
We took a ranger-led informational tour that ended in a brilliant sunset against dramatic clouds. The sand dunes here are spectacular and improbable.
The sand is composed of finely ground hydrated calcium sulfate, more commonly known as gypsum, that was blown in from ancient Lake Lucero, a vast drainage basin where dissolved minerals from sedimentary layers in the nearby San Andres and Sacramento Mountains collected, with no natural outlet. Water evaporated rapidly, leaving behind soft, large gypsum crystals (selenite) that wind eventually broke apart and tumbled into ever smaller grains that formed the dunes. This process continues to this day. Unlike sand, gypsum doesn’t absorb heat so it stays cool even in summer.
As the sun set behind the San Andres Mountains, the white sands kept the landscape visible even as it got dark (top photo). We could easily have spent another whole day here.