Devils Tower

Devils Tower is a monolithic igneous intrusion in the Black Hills of Crook County, Wyoming, rising about 386 meters above the Belle Fourche River. It formed roughly 40 million years ago when magma intruded into sedimentary rock and cooled underground, later exposed at the surface by erosion of the softer surrounding rock. The tower is famous for its columnar jointing: as the igneous rock cooled and contracted, it fractured into mostly hexagonal columns, among the most physically striking examples of columnar jointing on Earth. Geologists debate whether the rock body is the neck of an extinct volcano or a laccolith or stock that never reached the surface; in 1906 it became the first United States National Monument.