At a quick glance, you might mistake these dunes for massive snowdrifts. Although they do make for great sledding, the tiny crystals that form the dunes at White Sands National Park are not snow or ice but gypsum, a soft mineral often used to make plaster and chalk. The dune field became a national monument on this day in 1933 with a proclamation by President Herbert Hoover, which set aside nearly 150,000 acres for preservation. Recently, on December 20, 2019, President Trump signed legislation making it the 62nd designated national park in the National Park System.