Great Sand Dunes National Park and Preserve

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.[11] In the years that followed, the Rockies were gradually explored, treaties were signed and broken with resident tribes, and people with widely differing goals entered the San Luis Valley from the United States and Mexico.People had frequently speculated that gold might be present in the Great Sand Dunes, and local newspapers ran articles in the 1920s estimating its worth at anywhere from 17 cents/ton to $3/ton (equivalent to $3/ton to $46/ton today).[11] The park contains the tallest and widest sand dunes in North America,[7] rising to a maximum height of 750 feet (229 m)[6] from the floor of the San Luis Valley on the western base of the Sangre de Cristo Range.[8] The creation of the San Luis Valley began when the Sangre de Cristo Range was uplifted in the rotation of a large tectonic plate.The presence of larger rocks along Medano Creek at the base of the dunes, elsewhere on the valley floor, and in buried deposits indicates that some of the sediment has been washed down in torrential flash floods.Large amounts of sediment from the volcanic San Juan Mountains continued to wash down into these lakes, along with some sand from the Sangre de Cristo Range.The combination of opposing winds, a huge supply of sand from the valley floor, and the sand-recycling action of the creeks are all part of the reason that these are the tallest dunes in North America.This method takes core samples of sand from deep within a dune and attempts to measure how long quartz grains have been buried in the dark.[20] Great Sand Dunes National Park and Preserve is located in Saguache and Alamosa Counties, Colorado at approximately 37.75° north latitude and 105.5° west longitude.Two spring-fed creeks in the sand sheet along with a few small lakes in the valley's sabkha section southwest of the dunes create a wetland that nurtures wildlife.The San Luis Lakes State Wildlife Area lies adjacent to the southwestern corner of the park, while the Rio Grande flows through the valley farther to the southwest.The Baca National Wildlife Refuge lies adjacent to the west, and the slopes of the San Juan Mountains begin at the western edge of the valley.[24] The Great Sand Dunes are located in the high elevation desert of the San Luis Valley at about 7,694 ft (2,345 m), just west of the Sangre de Cristo Range.The mountain watershed receives heavy snow and rain which feeds creeks that flow down from alpine tundra and lakes, through subalpine and montane woodlands, and finally around the main dunefield.The recycling action of water and wind, along with a 7% moisture content below the dry surface holding the sand together, contributes to the great height of the dunes.When the water evaporates away in late summer, minerals similar to baking soda cement sand grains together into a hard, white crust.[32] Mammals include—from alpine tundra to low elevation grasslands—pika, yellow-bellied marmot, bighorn sheep, black bear, snowshoe hare, Abert's squirrel, gray and red foxes, cougar, coyote, mule deer, water shrew, beaver, porcupine, kangaroo rat, badger, pronghorn, and elk.From higher to lower elevations, and dependent on season, some of the bird species include the brown-capped rosy finch, white-tailed ptarmigan, red-breasted nuthatch, peregrine falcon, mountain bluebird, northern pygmy owl, dusky grouse, hummingbird (four species), western tanager, burrowing owl, bald eagle, golden eagle, sandhill crane, American avocet, and great blue heron.[40] Alpine tundra is the highest elevation ecosystem at Great Sand Dunes where the conditions are too harsh for trees to survive, but wildflowers, pikas, yellow-bellied marmots, ptarmigans, and bighorn sheep thrive.Bristlecone and limber pines grow at an extremely slow rate, with small statures that belie their true ages as some are more than a thousand years old.Cottonwood and aspen trees, red osier dogwood, and alder grow well in this wet environment, in turn providing shade and habitat for black bears, water shrews, and western tanagers.The sand sheet varies from wet meadows to the cool-grass prairie to desert shrubland, depending on proximity to groundwater and soil type.Elk and pronghorn are common, while burrowing owls nest in the ground and other raptors float through the skies searching for mice, kangaroo rats, and short-horned lizards.Wetlands speckle the San Luis Valley and are important habitats for sandhill cranes, shore birds, amphibians, dragonflies, and freshwater shrimp.[10] The park preserves the tallest sand dunes in North America,[7] as well as alpine lakes and tundra, mountain peaks over 13,000 feet (3,962 m) in elevation, mixed conifer forests, grasslands, and wetlands.[46] The road winds around the eastern side of the dune field, up through a forested mountain canyon inside the National Preserve, and then over Medano Pass—elevation 9,982 ft (3,043 m)[5]—at the 11.2 mi (18.0 km) mark.Camping is permitted in most places in the national preserve and at designated sites along the Medano Pass Road, as long as minimum impact guidelines are followed.[54] The restrictions of a wilderness designation protect native wildlife such as the endemic Great Sand Dunes tiger beetle from potential extinction caused by human activities.[53] The IUCN has included the same 51 square miles (132 km2) of dunes and surrounding sand sheets on their global list of wilderness areas (management category Ib) since 1976.