National Geographic: “I think anybody who has spent time looking at a variety of field sites around the world may come up with places that this might be happening,” says river geomorphologist Ellen Wohl of Colorado State University. “I can think of one place right off the top of my head,” she says, pointing to the rugged Big Box Canyon of Arizona, an area popular for its waterfalls and swimming holes. The study authors also point to the plunge pools of the Seven Teacups in California as another candidate.

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