Great Sand Dunes National Park and Preserve is a national park of the United States that conserves an area of large sand dunes on the eastern edge of the San Luis Valley, and an adjacent national preserve in the Sangre de Cristo Range, in south-central Colorado.
The park contains the tallest sand dunes in North America, up to 750 feet (230 m) tall. The dunes cover an area of about 30 sq mi (78 km2) and are estimated to contain over 1.2 cubic miles (5 billion cubic metres) of sand.
Sediments from the surrounding mountains filled the valley over geologic time periods. After lakes within the valley receded, exposed sand was blown by the predominant southwest winds toward the Sangre de Cristos, eventually forming the dune field over an estimated tens of thousands of years. The four primary components of the Great Sand Dunes system are the mountain watershed, the dune field, the sand sheet, and the sabkha. Ecosystems within the mountain watershed include alpine tundra, subalpine forests, montane woodlands, and riparian zones.