Many visitors to Great Sand Dunes National Park and Preserve are mystified: Why is there a Sahara-like dunefield below alpine peaks that reach over 13,000 feet in Colorado? The answer is complex, but the two essential elements are here: Avast, arid, closed basin that lakes once covered and a mountain barrier with a low curve to funnel winds into this natural pocket. Learn more at https://on.doi.gov/2lU4nyW. Photo by Patrick Myers, National Park Service.