The Great Sand Dunes National Park and Preserve is a hiking, photography, and ecological wonderland. The park holds the tallest largest dunes in North America (some reaching over 750 feet in height!), has a seasonally flowing stream, and numerous access points.
Geology
The following is an excerpt from Colorado Rocks. Check the full text out for more information and even more cool geologic locations!
Located on the eastern side of the San Luis Valley, the massive dune field nestles in a bend beneath the precipitous Sangre de Cristo mountain range. The dunes and a surrounding sand sheet cover about 30 square miles and are estimated to be made of more than 5 billion cubic meters of sand.
Where does all the sand come from?
After Lake Alamosa drained about 440,000 years ago, winds from the southwest blew across the drying lakebed, carrying sand left behind from the dried lakebed. Winds blew this material to the northeast, where it got trapped at the base of the Sangre de Cristo Range. Exactly how long it took the huge pile of sand to accumulate is unknown. Erosion of two mountain ranges, the San Juans to the west and the Sangre de Cristos to the east, contributed to the sediment.
Grass and shrubs grow on the sand sheet that extends out from the main dune field on three sides. Although not as remarkable as the towering dunes, the sand sheet contains nearly 90 percent of the sand in the park and is the primary source of sand for the dunes. In addition, modern streams draining the Sangre de Cristos still bring sand directly to the dunes via Medano and Sand Creeks.
The streams also bring water, which stabilizes the dunes. During winter and spring, and after monsoonal storms in summer, streams and standing water can be found in the dune field. Digging a few inches into the dunes reveals wet sand year-round. Wet sand doesn’t blow away like dry sand, so this wet interior helps anchor the dunes in place. The water also allows grasses and shrubs to take root at the edges of the dune field, reducing the ability for the wind to move sand. Finally, as the water at the surface evaporates, minerals precipitate to form a hard crust. Look for the whitish crust on the side of the road as you approach the park. The crust forms anew with each drying season.
Although the predominant wind direction is from the southwest, winds from the east occur during storms, and together, these opposite-direction wind patterns cause the dunes to grow vertically as their sand material gets blown back and forth, piling up on itself. Reversing, transverse, star, and rare barchan dune types all occur here. Though generally quite stable, some dunes are migratory, and many change shape seasonally.
Logistics
The Great Sand Dunes are about a 4 hour drive south from Denver, CO and a 4 hour drive north from Albuquerque, NM. The town of Alamos, CO is the nearest city, and has abundant hotel and restaurant options for travelers.
Visitors to the park need to present a National Parks Pass (or similar), or pay a small daily fee.
Temperatures vary wildly year round. Winters bring snow and freezing weather, while late summers can top 100°. My favorite time to visit is fall, though water is more likely to be present in the spring or during the summer monsoon season.
Your turn
What’s your favorite thing to do at the Great Sand Dunes?