A surprising place to get wet -- but also a handy place to then get dry (except when it's raining) -- is Great Sand Dunes National Park and Preserve in Alamosa and Saguache counties in Colorado. One finds the obligatory dunes of sand here -- in fact, the tallest in North America, rising in one spot 750 feet above the floor of the San Luis Valley. But to get to a large swath of them, one must wade across one of several (usually shallow) streams flowing along the sand mounds' edge. Most visitors actually relish that opportunity. The streams erode the edge of the dune field, and sand is carried downstream. The water disappears into the ground, depositing sand on the surface. Winds pick up the deposits of sand, and blow them up onto the dune field once again. Photo by Carol Highsmith.