Many of the millions of visitors snapping selfies on the Grand Canyon’s rim have no idea that the ruddy limestone cliffs are pockmarked with caves. “There’s really more caves in the Grand Canyon National Park than any other place,” says Jim Mead, a paleontologist and director of The Mammoth Site in South Dakota. Carlsbad Caverns, for instance, boasts somewhere around 119, while the Grand Canyon probably houses hundreds. The network within the steep walls is filled with the remains of plants and animals—hidden reminders of the region’s cooler past. For…
