CRATERS OF THE MOON NATIONAL MONU MENT, a tract of about 39 sq.m. in south-central Idaho, U.S.A., set apart in 1924 as a Government reservation. It is a region of cones and craters formed by volcanoes which have probably been extinct for only a few centuries, and the name of the reservation was suggested by its resemblance to the surface of the moon. While the black lava and cinders allow only the scantiest flora and quickly absorb the very light rainfall, water is to be found in tunnels which were formed by eruptions through a partly formed crust. Lava stalactites and stalagmites in red and blue are striking features of these tunnels.