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From Native Americans to Fourteener climbers, Colorado has a long history of people enjoying our state's soothing hot springs. —Photo by Terri Cook

Colorado by Nature: Relaxing in a Rift

The geological story behind all those steaming hot springs in the Arkansas Valley.

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Last summer, after summiting Mt. Yale and hobbling back to our car, my 14-year-old son and I drove directly to Cottonwood Hot Springs to soak our aching muscles and tired feet. The therapeutic benefits of soaking in hot, soothing mineral waters is no secret; from Native Americans and European settlers to modern weekend warriors, there is a long history of people enjoying our state’s steaming hot springs.

Cottonwood Hot Springs is one of a series of geothermal resources that run north-south along the length of the Arkansas River Valley. The list includes the Mount Princeton Hot Springs Resort, built around the Heywood Springs along Chalk Creek and the Hortense Spring, whose temperatures rise to a scalding 185 degrees Fahrenheit, making it the hottest in the state. Salida Hot Springs Aquatic Center, the nation’s largest indoor hot springs facility, is fed by several of the two dozen springs located near Poncha Pass. Farther south, there are some great options in the San Luis Valley, including the Joyful Journey Hot Springs Spa and the clothing-optional Valley View Hot Springs.

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Hot springs are found where water from rain and snow percolates deep underground, where it’s heated by magma or unusually hot rocks. Once hot, the water becomes more buoyant, causing it to rise like a helium balloon until it emerges at the surface as a natural hot spring. The presence of all this hot water is thus a clue that the ground is unusually warm beneath the Arkansas and San Luis valleys. But why this is the case is a geologic question that likely has to do with the formation of the valley itself.

The Arkansas Valley is what geologists call a rift—a zone where the Earth’s crust and upper mantle are being slowly pulled apart like the center of a piece of saltwater taffy being stretched. As the region thins, warm, malleable material, like the bubble in a lava lamp, wells up to fill the gap, bringing scalding material much closer to the Earth’s surface—and to the water circulating through the crust.

This rift is enormous, stretching from Chihuahua, Mexico, to Leadville, Colorado. Because the Rio Grande River flows through a portion of it, geologists call it the Rio Grande Rift. The Colorado portion—at about 28 million years old or so—coincides with the highest parts of the Rockies, so many researchers think this rift is related to the collapse of the Rockies, which have grown so high that gravity is now beginning to tear them apart. This theory helps explain the presence of so many hot springs near the many high peaks that loom above the valley—and makes relaxing in a rift after climbing a Fourteener a quintessential Colorado treat.

Terri Cook, 5280 Contributor

Terri Cook is an award-winning freelance writer based in Boulder. More of her work can be found at down2earthscience.com.

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