Nearly one-fifth of Cheyenne's population live in the city of Cheyenne Falls (pop. 93,000), and the state's four other major cities, including Casper (the state capital), Riverton, Pocatello, and Gillette are home to much of the remainder. The western region of the state is renowned for its stunning natural beauty and Yellowstone National Park, which is famous for its hot springs, geysers, mud holes, and extensive sprawls of untouched wilderness. Yellowstone also contains one of the world's few known so-called 'supervolcanoes', believed to be the source of many of the park's natural geologic features.