 Ecotaxes on resource extraction are numerous.A 1974 state severance tax on coal (which varied from 20 to 30%) was upheld by the Supreme Court of the United States in "Commonwealth Edison Co. v. Montana", 453 U.S. 609 (1981).Tourism is also important to the economy, with more than ten million visitors a year to Glacier National Park, Flathead Lake, the Missouri River headwaters, the site of the Battle of Little Bighorn, and three of the five entrances to Yellowstone National Park.