Great Sand Dunes in south central Colorado are the tallest dunes in North America. They were created from sands deposited in a lage inland lake that once filled the San Luis Valley. The sand left behind after the lake disappeared is blown by predominant southwest winds toward a low curve in the Sangre de Cristo Mountains and accumulates in a natural pocket. During storms, secondary winds from the northeast blow back toward the valley, in the opposite direction, and cause the dunes to grow vertically. The best scientific estimate is that the dunes were created less that 440,000 years ago.
Below - View of Great Sand Dunes covered in snow.
