Great Sand Dunes National Park and Preserve is 2.6 times larger than Des Moines, Iowa.
Area: 235 km2 calculated
Des Moines is the capital and the most populous city in the U.S. state of Iowa. It is also the county seat of Polk County. A small portion of the city extends into Warren County. It was incorporated on September 22, 1851, as Fort Des Moines which was shortened to "Des Moines" in 1857. Wikipedia
Area: 606 km2 calculated
Great Sand Dunes National Park and Preserve is a United States National Park located in the San Luis Valley, in the easternmost parts of Alamosa County and Saguache County, Colorado, United States. Wikipedia