Great Sand Dunes National Park was established November 22, 2000, having been designated a National Monument in 1932. The park protects about 150,000 acres, in which occur the tallest sand dunes in North America, some rising up to 750 feet.
Image via Wikimedia Commons.
Geologists believe that a long-disappeared lake left the sand behind, trapped between two mountain ranges. Prevailing winds now push the sand to the downwind side of the valley, where it piles up. Activities include sand sliding, backcountry camping, and hiking.