Craters of the Moon National Monument and Preserve is a national monument and national preserve located in the Snake River Plain in central Idaho, U.S.A. It is along US 20, between the small cities of Arco and Carey, at an average elevation of 5,900 feet (1,800 m) above sea level. The protected area's features are volcanic and represent one of the best preserved flood basalt areas in the continental United States. The Monument was established on May 2, 1924.