CAPULIN MOUNTAIN NATIONAL MONUMENT, a tract of about 68o ac. in the extreme north-west corner of New Mexico, U.S.A., set aside as a Government reservation in 1916. It is a region of extinct volcanoes, the principal one being Capulin mountain which is about 1 m. in diameter at its base and rises 5,50o ft. above the plain. There are also numerous "plugs" or lava columns isolated by erosion from the softer rock which once surrounded them.