Yellowstone National Park was the first national park in the world.
It spans an area of 2.22 million acres (.9 m hectares), comprising lakes, canyons, rivers and mountain ranges.
It has many types of ecosystems, but sub-alpine forest is most abundant.
It is known for its wildlife (especially wolves, bears, elk and bison) and its many geothermal features, particularly Old Faithful Geyser.
It is located mainly in the U.S. state of Wyoming, although it also extends into Montana and Idaho.
It was established by the U.S. Congress and signed into law by President Ulysses S. Grant on March 1, 1872.
Native Americans have lived in the Yellowstone region for at least 11,000 years.
Organised exploration of YNP did not begin until the late 1860s.
Yellowstone Lake is one of the largest high-altitude lakes in North America and is centered over the Yellowstone Caldera, the largest supervolcano on the continent.
The caldera is considered an active volcano. It has erupted with tremendous force several times in the last two million years.
Half of the world's geothermal features are in Yellowstone, fueled by the ongoing volcanic activity.
Lava flows and rocks from volcanic eruptions cover most of the land area of Yellowstone.
The park is the centerpiece of the Greater Yellowstone Ecosystem, the largest remaining nearly-intact ecosystem in the Earth's northern temperate zone.