Yellowstone National Park is a 2,219,789-acre (898,317 hectares) wilderness area maintained by the National Park Service. It is located at the intersection of Idaho, Montana, and Wyoming, with the majority of its area in Wyoming. The park is popular for its abundant natural features, including calderas, geysers, hot springs, and wildlife. It was the country’s first national park, and it remains the largest national park in the continental United States.

Yellowstone became a national park in 1872. It was established by Congress “for the benefit and enjoyment of the people.” Since that time, millions of people have visited the park to take advantage of its hiking trails, scenic views, glimpses of popular sites such as the geyser called Old Faithful, and one of the largest hot springs in the United States, the Grand Prismatic Spring, which is known for its rainbow waters.

The geology of Yellowstone makes it unlike any other place on Earth. Magma under Earth’s crust is close to the surface, making the region volcanically active. The park includes three calderas, formed from volcanic eruptions 2.1 million, 1.3 million, and 640,000 years ago, respectively. Many features of the park are a result of heat from the magma transforming Earth’s surface.

Yellowstone also boasts a large variety of animal and plant species. More than 1,000 species of native plants grow in the park. Over 150 species of birds live in the park, along with reptiles, and fish in a number of distinct ecosystems. Notably, the park contains a dense mammal population, including herds of bison and elk, and large predators such as wolves, grizzly bears (Ursus arctos horribilis), and mountain lions (Puma concolor).