For America's 250th anniversary, what was the first U.S. national monument?

Devils Tower was the first U.S. national monument, established on September 24, 1906.

President Theodore Roosevelt created the monument under the Antiquities Act of 1906, which authorized presidents to protect significant historic and scientific landmarks on federal land. Devils Tower, a striking rock formation in northeastern Wyoming, became the first site designated under that authority.

The formation is a laccolithic butte made of igneous rock. Its tall, mostly hexagonal columns formed as magma cooled and later erosion removed surrounding rock. The Lakota name for the site is Mato Tipila, commonly translated as Bear Lodge.

Devils Tower is sometimes confused with Yellowstone, which became the first U.S. national park in 1872. It is also distinct from Mount Rushmore, a later national memorial in South Dakota. The 1906 designation created a new category of protected federal landmarks that now includes hundreds of national monuments.