UNITED STATES OF AMERICA
WYOMING
Park and Teton Counties

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Yellowstone National Park was established on March 1, 1872, by an Act of Congress signed by Ulysses S. Grant (1822–1885), 18th President (1869–1877) of the United States, and was “dedicated and set apart as a public park or pleasuring ground for the benefit and enjoyment of the people” and “for the preservation, from injury or spoilation, of all timber, mineral deposits, natural curiosities, or wonders [...] and their retention in their natural condition.” Yellowstone is the first and oldest national park in the world. The national park covers an area of 3,472 square miles (8,992 square km) and is situated in northwest Wyoming, its western and northern borders extending into Idaho and Montana, repectively. Yellowstone was designated an International Biosphere Reserve in 1976 (first area in the U.S.), and became listed as a World Heritage Site by the UNESCO in 1978 (first natural area in the U.S.) (see also list of other UNESCO heritage sites).

Approximately 10,000 thermal features, 200–250 active geysers (more than anywhere else in the world, the best known of course “Old Faithful”), the Grand Canyon of the Yellowstone River, more than 100 waterfalls, fossil forests and the size and elevation of Yellowstone Lake were the commanding features that led to the preservation of Yellowstone as a national park. Catastrophic volcanic eruptions of 'super-volcanoes', which have occurred here 2 million, 1.3 million and 600,000 years ago, have created the area. These eruptions have spewed out more than 2,500, more than 280, and more than 1,000 cubic kilometres of debris, respectively. The first and third eruption are among the largest eruptions known to have occurred on Earth. The last eruption created a caldera (basin) of 28 by 47 miles (45 by 76 km). Yellowstone is still one of the largest and most active calderas in the world. The central area of the caldera has risen by 34 inches (86 cm) between 1923 and 1984, and has then slightly subsided between 1985 and 1989.

The  Lower Falls of the Yellowstone River [left] are the tallest waterfall of the park (308 ft, 94 m).