By Ethan Shaw Updated Mar 24, 2022
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The Kiowa and Cheyenne legends describe a massive grizzly bear raking the spire of Devils Tower — known as Tree Rock to the Kiowa and the Bear’s Lodge to the Cheyenne — while people gathered at its base. While these stories add mythic flair, the scientific explanation involves molten rock and deep time.
Most geologists consider Devils Tower a classic example of an igneous intrusion that never breached the surface. The body of magma, likely a laccolith or stock, pushed into overlying Mesozoic sedimentary layers composed of sandstone, shale, and gypsum, which had been deposited when the region was frequently flooded by inland seas.
Between 50 and 60 million years ago, during the uplift of the Black Hills, the magma cooled underground to form phonolite porphyry. As it solidified, it fractured into the iconic hexagonal columns that give the tower its striking appearance.
Over millions of years, erosion stripped away the surrounding sedimentary strata. The harder igneous rock of the intrusion resisted weathering more effectively, allowing the tower to stand while the softer layers were worn away. Even today, wind, water, and freeze‑thaw cycles gradually break down the columnar joints, leaving debris at the base.
Not all experts agree on the exact nature of the intrusion. Earlier hypotheses suggested Devils Tower might be the remnant of a volcanic neck, while a 2011 study presented at the American Geophysical Union proposed it could be the collapsed remains of a crater‑filled lava lake.
