Great Sand Dunes National Park and Preserve is an American national park that conserves an area of large sand dunes up to 750 feet tall on the eastern edge of the San Luis Valley, and an adjacent national preserve in the Sangre de Cristo Range, in south-central Colorado, United States. The park was originally designated Great Sand Dunes National Monument on March 17, 1932, by President Herbert Hoover. The original boundaries protected an area of 35,528 acres.