Devils Tower was created by protusion of magma from deep layers of the earth through Cretaceous sedimentary layers approximately 56 to 66 million years ago. The magma cooled at a speed that allowed the formation of jointed columns with 4 to 6 sides. The surrounding sedimentary rock eroded leaving the igneous tower. There is debate whether this a volcanic vent and that the magma was extruded or that it was intrusive magma flow below ground to form a laccolith and subsequently was eroded to expose the igneous body.
The bulbous base at the foot of Tower is often cited as evidence that Devils Tower is a laccolith, rather than a volcanic vent.
Badlands National Park, South Dakota. Pinnacles overlook: Most of the erosion has occurred in white volcanic ash that was deposited starting 27 million years ago. Serious erosion began approximately 500,000 year ago when the High Plains became more elevated enhancing river flow.
Badlands National Park, South Dakota. Pinnacles overlook.
