What was the first site designated a national monument under U.S. federal law?

Devils Tower was the first site designated a U.S. national monument under federal law.

President Theodore Roosevelt proclaimed Devils Tower National Monument in Wyoming on September 24, 1906. He used authority granted by the Antiquities Act, which Congress had passed earlier that year to protect historic and prehistoric objects and places of scientific interest on federal land.

The formation is a dramatic igneous rock butte in the Bear Lodge Mountains of northeastern Wyoming. It rises about 867 feet from base to summit and is especially recognizable for its tall, polygonal columns. The monument’s designation protected the formation and a surrounding area of about 1,346 acres.

Devils Tower has longstanding cultural significance for Indigenous peoples, including the Lakota and Kiowa. The English name came from nineteenth-century descriptions, while several Native nations use names connected with bears or a sacred lodge. National monument status is distinct from national park status, although both are part of the National Park System.