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North America’s Highest Sandbox: Great Sand Dunes National Park

The most exotic hike in the United States is smack in the middle of the country: Welcome to Great Sand Dunes National Park.

We continue meandering until the sun starts dipping toward Utah. We find the perfect place to camp–a ridge that flattens out into a bench with commanding views of dunes and mountains. That’s when my calves begin to wail: A 1998 Belgian study showed that walking on sand requires 2.7 times more energy expenditure and 2.5 times more mechanical work than does walking on hard ground. Australian exercise physiologist (and sand-walking guru) Anthony Leicht later tells me that walking on sand is “like lifting weights at a gym–only this time you’re ‘working out’ without working out.” Translation: I’m wiped.

I slip into my sleeping bag and start to drift off, but not before realizing sand-camping’s sweetest perk: Find a deep soft spot, and the bazillion grains hugging your spine are like nature’s memory foam. I fall into a cradled, customized dream.

Great Sand Dunes sits on the eastern edge of the San Luis Valley, drifting against the 13,000-foot Sangre de Cristo Mountains like waves against a seawall. Some 5 million years ago, an enormous lake covered the valley floor; when it dried up–or, according to other theories, gushed through the Rio Grande Gorge–it left behind huge, flat deposits of sand. As prevailing winds out of the southwest funneled toward three nearby mountain passes (Mosca, Medano, and Music), the sand from the valley piled up against the steep slopes of the Sangres, some drifting to heights of more than 750 feet. Not only that, Medano Creek and Sand Creek carry sediment back down to the valley floor, which gets blown on top of existing sand.

Dunes look quiet and static, but they’re not. They squeak and fart. They whoosh and swish. On our second day, we wobble along the top of a so-called Chinese wall–a feature formed from constantly reversing winds that pile a dune into knife-edge crests. That’s when I feel that astonishing hum under my soles. The explanation, say scientists who study sand, is this: Avalanches of round specks rub against each other and form standing waves of grains, which make certain dunes vibrate like subwoofers. In fact, a few years ago, French physicists hauled home some Moroccan sand and recorded the music it produced–foghorns, galloping hooves, airplane roars. (Don’t exhaust yourself trying to find it on iTunes. It’s, umm, academic.) As I step aside to let Mike go past, we all forget our tired calves. Suddenly, walking on sand is like magic.

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