Colorado’s western slope is rich with hot springs – many of which have been harnessed for private spas, while others remain in a natural state. These pools of piping hot, sulphur-tinged water are the result of a number of events occurring over millions of years.

“Deep in the earth along faults, water is in contact with hot rocks,” explains Dr. Christine Siddoway, a geology professor at Colorado College. “The water gets heated and because it’s been heated, it’s energized to travel up toward the surface, where it can be enjoyed by humans.”

The fault lines criss-crossing the western slope act like a plumbing system for this rock-heated hot water to travel upward, according to Siddoway. This is what fills pools with perpetually hot water around the state.

These underground hot rocks that lead to consistently surfacing water stay hot for a few different reasons, depending on the part of the state.

“The southwest corner of Colorado is a fairly young volcanic area,” Siddoway says. “On human terms, it’s not young – we’re talking tens of millions of years ago – but geologically, that’s recent.”

If you go for a soak in Pagosa Springs or Durango, thank ancient volcanoes for their leftover heat. However, different geologic forces are at play in central Colorado.

“There is a major rift cutting through Colorado,” explains Siddoway.

It’s called the Rio Grande Rift and it stretches all the way from Mexico to somewhere around Leadville, CO.

“An area of rifting is a place where faults act to stretch the earth’s crust,” says Siddoway, “and geological rifts always have hot rocks.”

The Rio Grande rift is still active, so there is no need to fear that many of Colorado’s hot springs will cool off anytime soon. The rift is stretching, albeit at an inconceivably slow pace – though it would still be considered fast in geological terms, according to Siddoway.

“It’s sort of propagating northward towards Yellowstone, which is the most active geothermal area in North America,” she explains. “And if they do connect and those two things start to interact–one consequence will be even better hot springs.”

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