What was the first national monument established in the United States?

Devils Tower National Monument was the first national monument established in the United States.

President Theodore Roosevelt proclaimed Devils Tower a national monument on September 24, 1906, using authority provided by the Antiquities Act signed earlier that year. The dramatic rock formation rises above the surrounding landscape in northeastern Wyoming and is sacred to several Indigenous nations.

The Antiquities Act allowed presidents to protect landmarks, structures, and other objects of historic or scientific interest on federal land. Roosevelt’s proclamation created the first site in a system that later expanded to include archaeological locations, historic places, and natural features across the country.

Devils Tower is a striking geological formation of columnar phonolite porphyry. Its origin has been debated, but geologists generally agree that molten rock cooled underground and was later exposed by erosion. The site became famous internationally through the 1977 film Close Encounters of the Third Kind, although its protected status began decades earlier.