Great Sand Dunes have been continually forming for over 400,000 years. The Great Sand Dunes form when wind and water move sand. Most sand comes from the San Juan Mountains, over 65 miles to the west. Larger, rougher grains and pebbles come from the Sangre de Cristo Mountains. Sand and sediments from both ranges washed into a huge lake once covering the valley floor. As the lake shrank, prevailing southwesterly winds bounced sand grains to pile up beneath the Sangre de Cristos or to be washed back toward the valley floor. Northeasterly storm winds blast through mountain passes, piling dunes back on themselves and creating North America’s tallest dunes. Research suggests that the dunes are less than 440,000 years old.

The dunefield with the tallest dunes in North America spreads across 30 square miles (78 sq. km), a unique high-altitude desert environment surrounded by the other ecosystems such as wetlands, forests, woodlands, grasslands, and shrublands. These dunes are a place of extremes: the sand surface can reach 150 degrees F (65 degrees C) on a summer afternoon, or drop to minus 20 degrees F (minus 29 degrees C) on a winter night. While the top few inches are often dry, these dunes are moist year-round, kept wet by ongoing precipitation. This 7% moisture content by weight allows species such as Ord's kangaroo rat, Great Sand Dunes Tiger Beetle, scurfpea, and blowout grass to survive here. Many animals visit the dunes from other habitats, including elk, pronghorn, bison, coyotes, bobcats, and raptors.

Credits and Sources:

“Exploring the Parks from Streams to Summits,” National Park Service. http://www.nps.gov/grsa/planyourvisit/upload/grsa-unigrid_map-2014.pdf, Accessed on June 28, 2015.

“Natural Features and Ecosystems,” National Park Service. http://www.nps.gov/grsa/learn/nature/naturalfeaturesandecosystems.htm, Accessed on June 28, 2015.