Devils Tower is the first U.S. national monument, a dramatic volcanic plug in northeastern Wyoming.
President Theodore Roosevelt established Devils Tower National Monument on September 24, 1906, under the Antiquities Act. The law gave presidents authority to protect significant natural, cultural, and historic features on federal land; Devils Tower was the first place designated under it.
The tower is an igneous intrusion made of phonolite porphyry. Geologists believe magma pushed into surrounding sedimentary rock roughly 40 million years ago. As the surrounding layers eroded, the resistant core was exposed. Cooling produced the tower’s striking vertical columns, many of them hexagonal.
Devils Tower rises about 867 feet from base to summit and stands 5,112 feet above sea level. It is sacred to several Plains tribes, including the Lakota, who call it Bear Lodge. “Monument Valley” is a landscape, while Chimney Rock and Shiprock are separate formations and were not the nation’s first national monument.