Colorado's eastern plains contain more than 30,000 square miles of wind blown (eolian) deposits. These eolian deposits consist of particles transported and deposited by the wind. Fine-grained particles (dust) form loess deposits. Coarser-grained deposits form sand dunes of varying shape.

The map above shows the distribution of eolian deposits (yellow) in Colorado.

Although there are thousands of square miles of dunes on the eastern plains, Colorado's most famous dunes are in the San Luis Valley within the Great Sand Dunes National Park and Preserve (GSDNPP). 
Here, one can find North America's tallest sand dunes, at more than 700 feet high. In the GSDNPP one can find transverse dunes, parabolic dunes, copice dunes, barchan dunes, reversing dunes, and star dunes. Going for a hike in the dunes is an "other world" experience.