Lunar Crater National Natural Landmark in central Nevada protects the Lunar Crater volcanic field, a stark landscape of many craters and cinder cones recognized as a United States National Natural Landmark in 1973. Its best-known feature is Lunar Crater, a roughly 400-acre maar formed by volcanic explosions when magma interacted with groundwater. The area is also significant in space exploration history: in September 1972, NASA trained Apollo astronauts there to identify volcanic and geological features like those they might encounter on the Moon, including rover traverses. Among those who later used that training on lunar missions were John Young, Charlie Duke, Gene Cernan, and Jack Schmitt.