Geology
The pillar consists primarily of Brule clay interlayered with volcanic ash and Arikaree sandstone. The harder sandstone layers near the top have protected the pillar since it broke away from the retreating cliff line to the south. Chimney Rock rises approximately 286 feet (87 m) above its surroundings. The Spire is a remnant of the erosion of the bluffs at the edge of the North Platte Valley.
Read more about this topic: Chimney Rock National Historic Site