The Sacramento and San Andres Mountains, with the Tularosa Basin between them, took shape approximately 250 million years ago. Giant upheavals in the Earth's crust distorted the land along with the gypsum deposits, forcing them high into the air about 70 million years ago. Rainfall and melt water came from the mountains causing the gypsum to percolate out and the concentrated solutions were washed down the mountainsides. The gypsum solution accumulated in Lake Lucero, the lowest part of the Tularosa Basin. Water in the lake does not have any means of escaping except by evaporation, which leaves behind thin layers of crystallized gypsum, or selenite. Weathering then reduced these crystals to fine, sandy grains. Winds then carried the grains farther up the basin, and the grains piled in steep dunes that often reach as high as 15 m (50 ft). The winds carved more dunes and, while at the same time, carried small amounts of the gypsum grains by distances of up to 9 m (30 ft) a year.