Rain on the Great Sand Dunes Spiral Notebook

A storm drops rain on the Great Sand Dunes of the Sangre de Cristo mountains in southern Colorado. The seasonal Medano Creek (meaning sand dune in Spanish) flows at the foot of the dunes in spring and early summer. I visited the dunes once in the late summer, and there was no sign of the creek. Great Sand Dunes National Park and Preserve is in the San Luis Valley. Originally created as Great Sand Dunes National Monument in 1932, Great Sand Dunes National Park and Preserve was established by an act of the United States Congress in 2004. The park includes 44,246 acres, and the preserve protects an additional 41,686 acres. The park contains the tallest sand dunes in North America, rising about 750 feet (230 m) from the floor of the San Luis Valley on the western base of the Sangre de Cristo Range, covering about 19,000 acres. Researchers say that the dunes started forming less than 440,000 years ago. The dunes were formed from sand and soil deposits of the Rio Grande River and its tributaries that collect against the Sangre de Cristo Mountains to the east.