Great Sand Dunes National Park and Preserve is home to the tallest sand dunes in North America with some dunes rising 750 feet (230 m) above the San Luis Valley floor. Unique to the Rocky Mountain physiographic province, the high- altitude desert dunes of the park and preserve represent one of the most complex dune systems in the world. The 30 square miles (78 sq km) of Great Sand Dunes are part of a larger dune field that includes a relatively flat sand sheet and sabkha and covers 150 square miles (389 sq km). High velocity, bi- directional winds shape the dunes, which offer the visitor an exceptional experience of dynamic eolian processes and sand dune morphology.