The Great Sand Dunes of the San Luis Valley, now protected within a National Park, are a relatively new feature of Colorado's landscape. During the Pleistocene Ice Age, 2 million to 10 thousand years ago, mountain glaciers and heavy meltwater eroded the San Juan, La Garita and Sangre de Cristo ranges which flank the Valley; the Rio Grande River and its many tributaries spread a thick layer of this sandy debris across the basin. As the Pleistocene ended and the climate warmed, the San Luis Valley, cutoff from moisture by the surrounding mountains, became a high desert. Over the past 10,000 years, prevailing westerlies have carried the sand eastward and, funneled toward Medano and Mosca passes, dropped their cargo at the base of the Sangre de Cristos; this process continues today.
Rising 700 feet from the valley floor and covering 55 square miles, the Great Sand Dunes are the tallest sand dunes in North America; shimmering like a mirage and backed by the majestic Sangre de Cristo Mountains, they are a scenic and fascinating destination for any naturalist. This National Park, initially established as a National Monument in 1932, offers camping from April through October on a first-come, first-served basis; access to the Park is via Colorado 150, which heads north from U.S. 160, 18 miles east of Alamosa (or 5 miles west of Blanca). A nature center introduces visitors to the natural history and native flora/fauna of the dunes.
One would think that these vast, shifting dunes, themselves lying within a Valley that receives less than 10 inches of precipitation each year, would not harbor any vegetation. In fact, several plant species, including Indian ricegrass, blowout grass, scurf pea and prairie sunflowers are able to tap moisture and nutrients within the dunes. Kangaroo rats, able to metabolize their own water, inhabit the dunes which also harbor two endemic insects: the Great Sand Dunes tiger beetle and the giant sand treader camel cricket. Pinyon pine and ponderosa pine woodlands rise along the edge of the dunes and are home to black bear, mule deer, bobcats, porcupine and coyotes. Pinyon jays, Steller's jays, bushtits, mountain bluebirds, blue grouse, Townsend's solitaires and Lewis' woodpeckers are among the avian residents.