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

Devils Tower was the first national monument created in the United States.

President Theodore Roosevelt proclaimed Devils Tower National Monument on September 24, 1906, under the newly enacted Antiquities Act. The proclamation protected the striking rock formation in northeastern Wyoming and made it the first site to receive the national-monument designation.

Devils Tower is a dramatic igneous formation rising about 867 feet above the surrounding Belle Fourche River landscape. Geologists continue to discuss the precise way its columns formed, but the rock is widely identified as phonolite porphyry, an uncommon igneous rock.

The Antiquities Act gave presidents authority to protect objects of historic or scientific interest on federal land. Devils Tower is often confused with Mount Rushmore, which became a national memorial, and with Yellowstone, which was established as the first national park in 1872. The site also has deep cultural significance for several Indigenous nations.