Great Sand Dunes National Park, San Luis Valley, CO.
The San Luis Valley is a land of superlatives. It’s the size of Connecticut. It’s a vast bowl surrounded on all sides by high mountains—the Sangre de Cristo on the east and the San Juans to the west. Yet it’s as flat as the Great Plains. There’s usually so much haze that the far away mountain chains are invisible, contributing to the illusion that I stand in Hugotown, Kansas, where they lay down marbles and watch ’em roll away, the earth’s so flat.
And yet, I’m on top of 13,000 feet of sediment dredged from the surrounding mountains. The Valley is filled up with clay, sand and gravel from the Sangre de Cristo, and with ash and lava from the volcanic San Juans. Base to tip, that makes some of these mountains as tall as the Andes. No small feet.
The San Luis Valley represents the only real desert in the Colorado Rockies, but it’s green with cottonwood and willow, carpeted with farms and ranches. Underlain by a vast aquifer and watered by the Rio Grande, the San Luis is primed for development, and what may be the nation’s hugest subdivision may soon roll out like indoor-outdoor carpeting. So, catch the San Luis the way it is while you still can.
A rift stretching for 60 miles in an intermountain interruption, the San Luis, originally settled by the Utes and later by the Spanish and then other Europeans, extends from New Mexico in the south to Poncha Pass in Colorado in the north. On its east side, Blanca Peak punches up from the flats to the third highest mountain in Colorado. And there’s one other superlative anomaly in the vast Valley—the dunes.
If you look hard north as you drive Highway 160, you can see them glimmer like vast mounds of sugar at the base of the Sangre de Cristo. Wind and water drove the sand here from the distant San Juans at the far western edge of the valley. The sand accumulated against the unbroken wall of the Sangre de Cristo. Countervailing winds from the eastern ranges batted the sand back west. Neither east nor west, San Juan or Sangre de, wanted the sand.
The dunes swirled like a giant dust devil here for centuries of centuries, building igneous and quartz grains to great heights. The highest dune is 750 feet, tallest on the continent. On approach, the dune field looks like a mountain range. They’re far larger than the Sand Hills of Nebraska, the White Sands of New Mexico, the Coral Pink Sand Dunes of Utah, or the Indiana Sand Dunes beached against Lake Michigan.
Rising abruptly from the swaddled green farmland and deciduous gallery forests hard against the mountains, the barchans at first seem like artifacts piled here by hundreds of dump trucks. It’s a slice of Arabia’s Great Empty Quarter, but in southern Colorado. On approach from the road, the erg looks a couple miles across, perhaps the width of a couple hills.
I was on my way to the San Juans for a little playtime, but I was early for my rendezvous, so I decided on a day hike. I looked at a hike in Great Sand Dunes like a day at the beach. Unlike at real beaches, never go barefoot out on these. They’re a little darker than beach sand, so the surface here can hit a toasty 140.
On my way to conquer the few billion grains of quartzite, I crossed an immense sand flat that rose to the base of a barchanoid monster. A distant coyote limped across the plain, its image flickering in high heat. I started up the slipface on the leeside of the dune, and it was like eating soup with a fork. I zigzagged up the crests toward High Dune, the second highest in the Park at 650 feet. I followed the ridgelines, but was tempted to try the dark, semi-hard patches of hornblende that looked like cryptobiotic soil but weren’t. If the blackish sand wasn’t at too high of an incline, I didn’t sink. It was like chancing frozen snow. But after a few steps it would give way, and the patch would avalanche, and haul me down on its escalator to nowhere.
I tried different ways of walking. I looked down at the billions, maybe trillions of particles of sand. I guessed that if you grounded them down fine enough, they’d become a liquid, and eventually a gas. Hell, it was already like sloshing through a mountain of slow ice. On the ridges, tiny dust devils whirled in Spirographs, tickling the crest like flies gone haywire.
At the summit, I got a real feel for how extensive the dunefield is—30 square miles. On the east side of the sand sea, shallow windward slopes were mismatched with steep leeward inclines, forming transverse dunes like waves in an uneasy sea. Where the wind changed, counterdunes lipped the dune crests. Fringing the main dune field, crescent-shaped barchan dunes formed where the sand pinched out in the valley. Farther north where the mountains spun the wind in all directions, the crests of star dunes were blasted by the eddies. I grabbed a seat (easy enough to do) and faced west, where the San Juans loomed beyond the smog, sixty-some miles off. The wind drove glassine crystals into my face, and I flipped down my shades.
I was alone for awhile, but then a man in a suede Bradfield hat made it up. His name was Steve, an ex-geologist who now practiced law in Denver. We semi-skied down the dune together.
He pointed out the alluvial fans that swept out into pediments from Blanca Peak. I asked Steve if the Great Sand Dunes would become sandstone, and he said that, for that to happen, the dunes would have to be buried under enough pressure. They might erode away first, but they were, for the moment, structurally stable. Spurs of the dunefield migrated toward the mountains here, onto some grazing land there. They looked like sand traps in a giant’s golf course. But then again, the whole National Park was one massive bunker. And yes, when I made it back to my truck, I excavated a boatload of the stuff from each shoe. I heaved it all back into the dune.
I can’t remember much of my trip to the San Juans later that day, a trip which lasted a week. But I don’t think I’ll forget the great incongruity of Great Sand Dunes National Park.