Only 75 minutes from La Veta, Colorado, the Dunes are among the half dozen most spectacularly beautiful and interesting locations in Colorado. The dunes enclosed by the National Park cover 30 square miles and rise over 700 feet tall at their peak. Several dune systems around the world are higher or larger than these, but they are all a product of desertification. Colorado's dunes are unusual in that they occur in a relatively wet corner of the San Luis Valley. Sand particles are blocked in their migration by a pocket of the great wall of the Sangre de Cristo mountain range. Beneath the valley's wind-leveled surface, groundwater forms an immense subterranean lake.