Geologic and Geographic Processes Contribute to the Formation and Maintenance of the Great Sand Dunes
The location and surrounding geography of the Great Sand Dunes are tied directly to the geologic processes that created and continue to create the Sangre de Cristo Mountains, the San Juan Mountains to the west and the massive San Luis Valley that separates them. The towering Sangre de Cristo and San Juan Mountains and sweeping San Luis Valley (which is the largest alpine valley on Earth) are integral parts of the northern end of the east-west spreading Rio Grand Rift, which has been and continues to be formed by the spreading apart, by plate tectonic forces and processes, of the southwestern United States. The Sangre de Cristo Mountains, which form the east side of the Rio Grande Rift, and the San Juan Mountains, which form the western side of the Rio Grande Rift, are moving away from each other, east and west respectively, causing the San Luis Valley to drop down between them, forming a rift valley.
So, the tectonic rift formation of the Sange de Cristo Mountains and the San Luis Valley set the geographic stage for the formation of the sand dunes. The Great Sand Dunes themselves are formed where prevailing local winds that blow from west to east across the rifting San Luis Valley and are funneled through Medano Pass, which is a low point along the Sangre De Cristo ridgeline that sports numerous 13,000+ and 14,000+ foot high peaks. As the winds approach the choke point of Medano Pass, where they are pushed up and over the saddle pass in the San de Cristo Mountains, the wind speeds decrease dropping their sand load forming the Great Sand Dunes. The Medano River, and other streams that flow west out of the Sangre De Cristo Mountains, are continually eroding the eastern edge of the Great Sand Dunes front, and adding their own sand load, returning sand to the edges of the dune field, where the persistent west-toeast local winds again pick up the sand and refreshes the dunes. This process has been active for thousands of years and continues today.
The National Park and Preserve offers plenty of both developed and primitive camping. In addition to the dunes themselves there are myriad other recreational adventure opportunities including mountain pass and mountain front hiking trails as well as ORV paths. A 4-wheel drive path along the eastern front of the dunes at the base of the Sangre Cristo mountains, leads to several remote picnicing and camping sites, and offers numerous adventures in the dunes, along the dune's margins and in the mountains.
The Moody Dunes
Nestled into the base of the Sangre to Cristo Mountains these massive sand dunes experience constant changes in light and weather which can dramatically morph the mood of the dunes, sometimes from moment to moment. One moment the dunes standout in high contrast and relief against the sky and mountains, and a few minutes later the atmosphere and light shift and the dunes dissolve into the surrounding luminance and clouds. The following three images show mood changes that occurred during just one hour of one afternoon. So, haul out your camp chair, park it beside your cooler with a couple sandwiches and watch the show!
In The Dunes
As beautiful as they are from afar, these giant dunes are also dramatic up close, and particularly when viewed and experienced from the inside out. Don your sneakers or hiking boots, dress in layers (the weather can change dramatically in a short period of time and the interior of the dunes are usually windier than the surrounding areas) and bring some water and a few snacks, and then head out across the flats to the base of the dunes. Plan to take your time, and take frequent breaks. Walking in the deep sand is very fun but also slow going, which is just fine, because you want to enjoy looking around and taking in the scenery. Hiking up and along the dude ridges is typically easier than trying to assault the faces, although sand skiing down the steep faces is a hoot. It can be quite windy, which is to be expected because, well, these are wind blown sand dunes ;-).
Pay attention to and enjoy the incredible geometric shapes that are present on many scales, from the constantly changing and migrating textures and patterns of the moving sand ripples to the long and gracefully arcing ridges that define the beautiful shapes of these amazing dunes. Be sure to also marvel at the visual contrast between the lovely smooth-surfaced dunes and the soaring, craggy ridgelines of the Sangre do Cristo mountains. Each dune top ridge you gain, offers new, different and thoroughly astounding views! Perhaps the most compelling feature of these dunes is the light and how it changes from moment to moment and throughout the day.
The reason why these Great Sand Dunes are here, are the location of three mountain passes, Music, Medano and Mosca, which are located just to the esst of the dunes, and offer the passage of air, and hikers, up and over in the high Sangre de Cristo mountains ridge line. Numerous 13,000-14,000 foot peaks define the Sangre de Cristo crest. The significantly lower, 7000-8,000 foot, passes provide of the prevailing west to east winds that blow across the arid, dry and sandy San Luis Valley a release valve and an escape route. These constantly flowing winds that funnel through the three passes move the sand across the San Luis valley, which is then deposited as the wind velocity is reduced as it approches the base of the mountains and begins to move up, over and through the low passes. Steam channels, such as Medano Creek, which flow down from the mountains, pick up the deposited sand and moves it back west toward the San Luis Valley, where the wind picks it back up and delivers it again to the dunes. This circular process that forms and maintains these giant and glorious dunes has been active for thousands of years.
Autumn Around Great Sand Dunes National Park and Preserve
Autumn is a special time at Great Sand Dunes National Park and Preserve. October in particular, with its low angle sunlight, warm natural lighting, fall colors at lower elevations and early winter snows on the surrounding high peaks and ridge-lines provide a particularly delightful plethora of natural features and environments to delight all of your senses.