Great Sand Dunes National Park and Preserve is a United States National Park located in the easternmost parts of Alamosa County and Saguache County, Colorado, United States. Originally designated Great Sand Dunes National Monument, Great Sand Dunes National Park and Preserve was created by an act of the United States Congress on September 13, 2004. The park contains approximately 85,000 acres including the tallest sand dunes in North America, rising about 750 feet from the floor of the San Luis Valley on the western base of the Sangre de Cristo Range, covering about 19,000 acres. They are perhaps 12,000 years old
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