Craters of the Moon National Monument and Preserve is a U.S. national monument and national preserve in the Snake River Plain in central Idaho. It is along US 20, between the small towns of Arco and Carey, at an average elevation of 5,900 feet above sea level. The Monument was established on May 2, 1924. In November 2000, a presidential proclamation by President Clinton greatly expanded the Monument area. The 410,000-acre National Park Service portions of the expanded Monument were designated as Craters of the Moon National Preserve in August 2002. It spreads across Blaine, Butte, Lincoln, Minidoka, and Power counties. The area is managed cooperatively by the National Park Service and the Bureau of Land Management. The Monument and Preserve encompass three major lava fields and about 400 square miles of sagebrush steppe grasslands to cover a total area of 1,117 square miles. The Monument alone covers 343,000 acres. All three lava fields lie along the Great Rift of Idaho, with some of the best examples of open rift cracks in the world, including the deepest known on Earth at 800 feet.