Yellowstone National Park is a U.S. Biosphere Reserve, a World Heritage Site, and one of the largest national parks in the lower 48 states. Its boundaries protect over 10,000 geysers, hot springs, mudpots, and steam vents, the earth's largest array of geothermal features. A vast wilderness habitat also protects an incredible variety of wildlife, including some threatened and rare species. Geysers and hot springs played a compelling role in the park's establishment. Since then, the Yellowstone area has become valued for many other things: wildlife, scenery, recreation, wilderness, and natural processes. Here, these elements make up the Greater Yellowstone Ecosystem, a place where all things share complex, interdependent relationships.