Public Domain Image: NPS
White Sands National Monument, established on this date in 1933, is in southern New Mexico. The 144,000 acre monument protects about 225 square miles of spectacular dunes made of calcium sulfate, or gypsum. Several natural processes deposited the dunes over eons, and those forces continue to shape the dunes today. Activities include driving tours, a few relatively short hiking trails, and dune sledding.