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 square miles (8,987 km2), mostly within the north west corner of Wyoming, but with portions extending into the states of Idaho and Montana.