On U.S. Route 70, in between Las Cruces and Alamogordo, we came across a geologic formation called the Tularosa Basin, a graben (trench) basin, formed by fault lines pushing up adjacent rock formations, creating a center low point. Gypsum dissolves from the surrounding Sacramento and San Andres Mountains and slides down into the basin. Gypsum is water soluble and, usually, is carried off during rains to the nearest river and taken to sea. But, because the #TularosaBasin is fully enclosed, the #gypsum is completely trapped, creating White Sands National Monument (@whitesandsnps), the largest, gypsum dune field in the world. Over thousands of years, the soft clear crystals have become worn and scuffed and white from the friction of the elements. During the Pleistocene, two-and-a-half million years ago, this basin was a giant glacial lake, called Lake Otero, which later dried out at the close of the Ice Age, 11,000 years ago. Have you been to this stunning place?