What was the first U.S. national monument, established in 1906?

Devils Tower National Monument, established in 1906, was the first national monument in the United States.

President Theodore Roosevelt proclaimed Devils Tower a national monument on September 24, 1906, under the Antiquities Act. The law, passed earlier that year, authorized presidents to protect historic landmarks, prehistoric structures, and objects of scientific interest on federal land without waiting for a new act of Congress.

Devils Tower is a striking igneous formation in northeastern Wyoming. It rises about 867 feet above the surrounding Belle Fourche River valley and is composed of phonolite porphyry, an unusual rock type. Geologists generally describe it as the exposed core of an ancient volcanic intrusion.

The monument is also culturally important to several Indigenous nations, including the Lakota and Kiowa. The name and climbing practices have been subjects of continuing discussion. Mount Rushmore and Grand Canyon National Monument were created later.