White Sands National Monument is not what I expected. I’ve been to and hiked around numerous sand dune formations in deserts – and, probably, more than dozens at beaches – and I expected the sand dunes at White Sands to be more like Eureka Dunes or the main dune field in Death Valley. They aren’t and not just because they are white – slightly gray on our trip because, I’ve since learned, they were damp from a recent rainfall – they also have a different texture and are much lower than I expected. This is because they are gypsum – hydrous calcium sulfate, if you prefer – not quartz, silicon dioxide, most of us are used to. Sand, it turns out, is defined by size, not material (according to Wikipedia, it is “finer than gravel and coarser than silt”.
What I don’t know is how all this gypsum got here. What I do know is that this area shares a similar general history to the nearby – relatively speaking, that is – Carlsbad and Wolfcamp areas. About 280 to 250 million years ago, the land on earth was one supercontinent – with some smaller island arcs and isolated islands – which geologists have named Pangaea. As an aside, Pangaea was not the only supercontinent. The basis of modern geology is that the plates – sections of earth, imagine the different sections of a soccer ball – move around, driven by currents deep in the liquid core of the earth. These plates have, over about 4.5 billion years, come together to form supercontinents more than once, more likely more than five times, building mountains and raising seabeds and then bounced or drifted apart forming isolated land masses like North America or Africa. End aside. Anyway, at the edge of Pangaea was a shallow sea in which, over millions of years, layers of sediment collected. In this local area – and this is what I don’t quite understand, why only here? – gypsum, which is water-soluble, collected in the layers. About 70 million years ago, the Farallon Plate started slipping under the North American Plate lifting this part of the world, exposing the layered gypsum. About 30 million years ago, the Farallon Plate also started stretching the earth apart in this area, with the Nevadan Basin and Range, and the land that is now White Sands National Monument dropped, forming the large basin we drove into a couple of hours ago. About 24 to 12 thousand years ago, during the last Ice Age, large amounts of gypsum were washed into the basin, forming a lake without an outlet. Recently, geologically speaking, that lake dried up exposing the gypsum deposits, crystallizing them, and winds have blown the now sand into what is now White Sands National the Monument, for us to enjoy on a warm afternoon.