If "Frozen" traded ice for sand, the result would look a lot like White Sands National Park in New Mexico—cool, white dunes that deceive the eye at first glance. It became a national monument on this day in 1933, established to protect a rare geological phenomenon: the world"s largest gypsum dunefield. These dunes were formed from gypsum crystals that broke down over thousands of years, creating bright waves that stay cool even in summer.