There are two basic types of underground mining methods: room and pillar and longwall. In room and pillar mines, coal is removed by cutting rooms, or large tunnels, in the solid coal, leaving pillars of coal for roof support. Longwall mining takes successive slices over the entire length of a long working face. In the United States, about two-thirds of the coal recovered by underground mining is by room and pillar method; the other third is recovered by longwall mining. Coal seams in the United States range in thickness from a thin film to 50 feet (15 meters) or more. The thickest coal beds are in the western states, ranging from 10 feet (3 meters) in Utah and New Mexico to 50 feet (15 meters) in Wyoming. Other places, such as Great Britian, use the longwall method.