Great Sand Dunes National Park - The Great Sand Dunes near Alamosa, Colorado represent a rather unique gesture of Nature.
Sand is carried in by winds that are funneled through a gab in the Sangre de Cristo mountain range. This gap creates mini low pressure system causing percipitation. The sand carried in by the winds and rain drop onto the Dunes while the rain and the melt water in spring carry the water back out into the plains concluding the cycle. Amazingly the current shape of the Sand Dunes did not change very much over a century. This was revealed through photographs that can be seen at the visitors center.

Great Sand Dunes National Park, Alamosa, Colorado