Long before any recorded human history in Yellowstone, a massive volcanic eruption spewed an immense volume of ash that covered all of the western U.S., much of the Midwest, northern Mexico and some areas of the eastern Pacific. The eruption dwarfed that of Mt. St. Helens in 1980 and left a caldera 30 miles wide by 45 miles long.

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Northern Rocky Mountain wolves, a subspecies of the gray wolf (Canis lupus), were native to Yellowstone when the park was established in 1872. Predator control was practiced here in the late 1800s and early 1900s. Between 1914 and 1926, at least 136 wolves were killed in the park; by the 1940s, wolf packs were rarely reported. By the 1970s, scientists found no evidence of a wolf population in Yellowstone; wolves persisted in the lower 48 states only in northern Minnesota and on Isle Royale in Michigan. An occasional wolf likely wandered into the Yellowstone area; however, no verifiable evidence of a breeding pair of wolves existed through the mid 1990s.

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Most tourists to Yellowstone do not realize it, but they are standing atop the largest, most destructive type of volcano on Earth.

Beneath the Yellowstone region lies the largest active magmatic (molten rock) system in North America. Yellowstone's volcanism is responsible for the world's largest, most diverse collection of spectacular geysers, natural hot springs, mud pots, and steam vents.

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