Which 1906 site in Wyoming became America’s first national monument?

Devils Tower became America’s first national monument in 1906.

President Theodore Roosevelt proclaimed the monument on September 24, 1906, under the newly enacted Antiquities Act. The isolated volcanic formation rises dramatically above northeastern Wyoming’s plains and became a landmark associated with the American frontier.

Devils Tower is a laccolith, an igneous intrusion formed when magma hardened beneath the surface and was later exposed by erosion. Its distinctive vertical columns make it one of the most recognizable geological features in the West.

The site is sacred to several Northern Plains tribes, including the Lakota and Kiowa. The name “Devils Tower” comes from a 19th-century translation error, while many Indigenous communities use traditional names for the formation.