Today we celebrate the birthday of Great Sand Dunes National Park and Preserve, which boasts 750-foot (and higher) sand dunes that cover more than 30 square miles. But the towering hills of sand—the tallest in North America—are just one feature of an eye-popping Colorado landscape that includes conifer forests, alpine lakes, and wetlands. The 150,000-acre park and preserve even encompasses stretches of tundra at the higher elevations, where it edges up against the base of the Sangre de Cristo Mountains.