What is Yellowstone?

Yellowstone National Park is the first national park in the United States and the world, established by an Act of Congress signed by President Ulysses S. Grant on March 1, 1872, covering about 3,468 square miles primarily in northwestern Wyoming with smaller portions in Montana and Idaho. Yellowstone is famous for its geothermal features, abundant wildlife, dramatic landscapes, and central role in the history of conservation.

The park sits atop the Yellowstone Caldera, a giant volcanic crater about 30 by 45 miles formed by three massive eruptions over the past 2.1 million years. Heat from the underlying magma chamber drives more than 10,000 hydrothermal features, including geysers, hot springs, mud pots, and fumaroles, more than half of the world's total. Old Faithful, the most famous geyser, erupts approximately every 90 minutes, sending water 100 to 180 feet into the air for about 1.5 to 5 minutes.

Other notable thermal features include Grand Prismatic Spring (the largest hot spring in the United States and one of the most colorful in the world due to thermophilic bacteria), Castle Geyser, Steamboat Geyser (the world's tallest active geyser when it erupts), Mammoth Hot Springs (with travertine terraces), and Norris Geyser Basin (the hottest and most acidic). The park also contains the Grand Canyon of the Yellowstone, a 24 mile long, 800 to 1,200 foot deep canyon featuring the Upper and Lower Falls of the Yellowstone River.

Wildlife includes grizzly bears, black bears, gray wolves (reintroduced 1995 to 1996 after extermination), elk, bison, moose, mountain lions, bobcats, lynx, eagles, ospreys, bighorn sheep, mountain goats, and many smaller species. The park's bison herd, about 5,000 animals, is the largest free-ranging herd in the country and descends from the survivors of the near-extermination of bison during the late nineteenth century, when only about 23 wild bison remained at one point.

The park is administered by the National Park Service, which was established as a federal agency on August 25, 1916. Yellowstone draws about 4 million visitors annually. Notable historic sites within the park include the Old Faithful Inn (1903), one of the largest log structures in the world, and the Roosevelt Arch at the north entrance dedicated by President Theodore Roosevelt in 1903.

The park is part of the larger Greater Yellowstone Ecosystem, one of the last large nearly intact temperate ecosystems in the world, covering about 22 million acres including the park itself plus surrounding national forests and Grand Teton National Park.