What was the first U.S. national monument designated under the Antiquities Act?

Devils Tower was the first U.S. national monument designated under the Antiquities Act.

President Theodore Roosevelt proclaimed Devils Tower National Monument in Wyoming on September 24, 1906. The designation came soon after Congress passed the Antiquities Act, which authorized presidents to protect significant historic, prehistoric, and scientific objects on federal land.

Devils Tower is a striking igneous rock formation that rises about 867 feet above the surrounding landscape. Geologists debate the details of its formation, but its columns are widely understood to have formed as molten rock cooled and contracted. The site also has deep cultural importance for several Indigenous nations.

The monument is sometimes confused with the Grand Canyon, which became a national monument in 1908 and a national park in 1919. Devils Tower was not the first national park; Yellowstone held that distinction. It was the first site protected through the new national-monument authority.