Exploring

Colorado’s Great Sand Dunes: A True Wonder of the West

By Vivian Underhill, 7-13-11

	Great Sand Dunes National Park. Photo by Flickr user Ed Siasoco.

South of Denver by about four hours, the Sangre de Cristo mountain range looms over the dusty sagebrush of the San Luis Valley. Named for the dark shades of crimson and lavender that radiate from its west-facing rock each evening, this range is stunning – and worthy of a healthy respect. It’s home to Little Bear Peak, widely considered one of Colorado’s most dangerous 14ers, among myriad other mountains.

These two opposing ecosystems – desert and alpine – are stitched together by the Great Sand Dunes. I visited them recently, somewhat against my will; a few out-of-state friends badgered me into going with them, saying that, as a Colorado native, I had no excuse to miss one of my state’s great monuments. At the time, I only sniffed snobbily: regardless of the fact that they’re made of sand, they’re really only hills. But in retrospect, they were exactly right, and I’m incredibly glad I gave in to them.

The evening the four of us arrived, we raced up the dunes barefoot (inasmuch as it’s possible to race up slipping sand).

Every minor ridge we crested gave way to nothing but more ridges beyond, and the sheer immensity of this pile of sand only gradually dawned on us. They say the sky contains more stars than all the grains of sand on Earth, and while I’m not doubting that wisdom on theoretical grounds, on more practical grounds I have to disagree.

Sitting on a big dune, letting sand run through our hands and watching it slow-motion avalanche below our feet, we avowed that the grains contained in these dunes alone must far outstrip the sky’s measly stars in number. I like to think I’ve seen impressive things in my time, but just trying to imagine the matrix of grains that lay between me and the ground – a thousand feet below me – made my brain hurt. I sometimes think our brains have only a limited capacity to make sense of grandeur, and this was definitely testing that limit. So when my friends asked me how the Sand Dunes came to be here, I was only too happy to fall back on all-powerful science to make sense of it all. 

This is what I know, or have learned recently. First off, I’ve been taught since elementary school about the great sea that covered much of this region millions of years ago, in the Paleozoic era. It eventually receded, leaving great flat areas like the San Luis Valley inundated with nothing but a sandy, restless soil where only the hardiest of desert shrubs subsist. Now, the constant wind picks up sand from the westernmost edge of the valley as it races down the backs of the San Juan Mountains, and drags it west.

Grains scud along the ground, becoming shifting dust devils across the highway and creating a haze in the sky, only to be deposited at last when the wind runs headlong into the Sangres and is forced up and over.

I also happened serendipitously across a book ("Wind" by Jan DeBleu) that describes exactly how sand moves with the wind. As the wind picks up, a basic grain of sand begins by merely rolling, acquiescing to movement in the least dramatic way possible. As soon as it runs into a rut in the road, though, it gets catapulted into the air unceremoniously only to land carrying more force than it began with. It’s sent back upward again, and again, its path growing higher with each consecutive bounce, in a process collectively known (apparently) as saltation.

What happens next is my favorite part. In a perfect example of the omnipresent feedback cycles inherent in natural processes, each time a grain of sand lands back on the surface, it creates a small dent, just the perfect size to disrupt another rolling grain’s movement and send it flying as well.

Enough years (or thousands or millions of years) of the same basic process, and enough sand, and eventually the Sand Dunes are what you get. Pretty magnificent, isn’t it? And I’ll never look down my nose at mere dunes again.

Vivian Underhill writes the ”Boulder Frugalista” column, which runs every Tuesday in the Colorado Daily. She grew up in Boulder, in a family of mountain climbers, and enjoys trail-running, rock climbing and all manner of winter adventures. She’s studying environmental sciences at CU Boulder.

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