Yellowstone National Park is a United States National Park and a UNESCO World Heritage Site. It was the world's first national park, set aside in 1872 to preserve the vast number of geysers, hot springs, and other thermal areas, as well as to protect the incredible wildlife and rugged beauty of the area. The park contains 3,472 sq mi (8,990 km2), mostly within the northwest corner of Wyoming, but with portions extending into the states of Idaho and Montana.
On March 1, 1872, Yellowstone became the first National Park reserve declared anywhere in the world, by President Ulysses S. Grant. In 1978 it was designated a World Heritage Site. Although it is commonly assumed that the park was named for the yellow rocks seen in the Grand Canyon of the Yellowstone, the park's name comes from the Yellowstone River that flows through it, which is in turn named after sandstone bluffs found farther down its course in eastern Montana.
The park is the core of the Greater Yellowstone Ecosystem, one of the largest intact temperate zone ecosystems remaining on the planet, and as a result is an exceptional area for wildlife viewing.