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Some 1,350 species of flowering plants (roughly 1,150 of them native) have been identified in Yellowstone. About four-fifths of the park’s area is forested, and the vast majority of the tree growth consists of lodgepole pines. Among the several other conifer species in the park are whitebark pine, found at higher elevations, especially in the Absarokas; and Douglas firs, which dominate at lower elevations, notably in northern areas. Cottonwoods and willows grow along streams, and stands of aspens occur in many sections. Hundreds of types of wildflowers thrive in a variety of habitats. The earliest blossom in April and the latest in September. Common species include phlox, lupines, cinquefoils, larkspurs, and Indian paintbrushes.

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Animal life in Yellowstone is typical of the Rocky Mountain West, and the park boasts the greatest assemblage of mammals—more than five dozen species—in the United States, outside of Alaska. Bison (buffalo), the largest of the mammals, were brought back from near extinction at the beginning of the 20th century. They now constitute several thousand head divided into two subpopulations that, respectively, inhabit summer breeding grounds in the Hayden Valley (north-central) and Lamar Valley (northeast) areas of the park. Other large mammals often seen in Yellowstone include elk (wapiti), mule deer, black bears, foxes, and coyotes. There are smaller populations of brown (grizzly) bears, bighorn sheep, pronghorns, mountain goats, and moose. Bobcats are thought to be present throughout the park, but their numbers are unknown, and there are occasional sightings of lynx and pumas (mountain lions). Common smaller mammals include badgers, martens, weasels, river otters, hares and rabbits, shrews, a variety of bats, and many species of small rodents. Wolves were successfully reintroduced into Yellowstone in 1995 and are now found throughout much of the park. Beavers have also made a significant comeback, and several hundred live along streams and lakes, mainly in the northwest, southeast, and southwest.

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More than 300 different species of birds have been identified as living year-round or seasonally in Yellowstone or migrating through the park in spring and autumn. Roughly half of that total nest there during the summer. Songbirds and woodpeckers constitute the greatest number of species. Among the permanent residents are jays, chickadees, nuthatches, ravens, and waterfowl such as trumpeter swans and Canada geese. Summer breeders of interest include sandhill cranes, white pelicans, and common loons—with Yellowstone representing one of the southernmost points that the latter group reaches in North America. The populations of three of the park’s raptors—bald eagles, ospreys, and peregrine falcons—have made significant recoveries after having been severely depleted in the mid-20th century. Each species has been the subject of a long-term study and monitoring program in Yellowstone.

Most of the park’s lakes and streams have natural fish populations, but many are located above waterfalls and other impediments and have introduced populations. For decades Yellowstone’s waterways were stocked with fish—including three indigenous sport species (cutthroat trout, Arctic grayling, and Rocky Mountain whitefish) and several nonnative species (mainly trout)—but that practice was ended in the 1950s. Some of the more remote lakes and streams subsequently reverted to their fishless state. Concerns over depleting stocks of native sport fish prompted park officials to implement stringent fishing regulations that included a catch-and-release policy for those species.

Fewer than a dozen reptile and amphibian species are found in Yellowstone, in large part because of the region’s cold and relatively dry climate. Notable types include prairie rattlesnakes (Crotalus viridis), the only venomous species in the park; boreal chorus frogs (Pseudacris triseriata maculata), known for the loud call of the males during breeding season; and blotched tiger salamanders (Ambystoma tigrinum melanostictum), which are common in fishless lakes and ponds.

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Also of note are the many varieties of thermophiles (heat-tolerant extremophiles) that thrive in the park’s hydrothermal features and are responsible for many of their distinctive colors. Prokaryotic types—e.g., varieties of algae and bacteria—can be found in such features as Norris Geyser Basin and Mammoth Hot Springs, respectively. Thermophilic archaea—which can survive in the most extreme conditions—are found in features throughout the park, including Mud Volcano along the Yellowstone River north of Yellowstone Lake, Grand Prismatic Spring in Midway Geyser Basin, and Roaring Mountain north of the Norris area.

Early history and creation of the park

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Archaeological evidence recovered in Yellowstone indicates that there has been a sustained human presence in the region since sometime after the end of the last glaciation there (about 13,000 to 14,000 years ago), with the oldest artifacts dating to more than 11,000 years ago. Little is known about those early peoples. Wind River Shoshone (also called Sheep Eaters) are thought to have arrived in the Yellowstone area about 1400 ce. Many other groups followed, and those peoples either lived in or near the land now occupied by the park or visited the area to hunt, trade, or conduct ceremonies.

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The first person of European ancestry to venture into the Yellowstone region was American trapper and explorer John Colter, who reached the area in 1807–08 after having been part of and then leaving the Lewis and Clark Expedition in 1806. Other trappers—including Jim Bridger, Joseph Meeks, and Osborne Russell—told of seeing the canyon, lake, and geysers. The first published account of the region was by Daniel Potts, whose letter to his brother vividly describing Yellowstone Lake and the West Thumb Geyser Basin appeared in a Philadelphia newspaper in 1827. Another trapper, Warren Angus Ferris, visited Yellowstone and was the first to use the name geyser for the hydrothermal features there. Ferris, who was a trained surveyor, prepared a map of the Yellowstone area in 1836. An official government party led by Capt. William F. Raynolds failed to reach Yellowstone in 1860, but the well-planned Washburn-Langford-Doane and Hayden expeditions of 1870 and 1871, respectively, undertook thorough surveys of the region.

Proposals for the federal government to protect the Yellowstone region had first been voiced in the mid-1860s, about the same time that such ideas were also being debated for the Yosemite area in California. Part of the impetus was through Jay Cooke and his Northern Pacific Railway Company, which was building a rail line from Lake Superior to the Pacific Northwest that passed just north of Yellowstone. Ferdinand Vandiveer Hayden, upon returning from leading the 1871 survey, had informed Cooke that Yellowstone was commercially suited only for recreation. Cooke (seeing the potential for tourism), along with returning members of the 1870 and 1871 journeys and others, became strong advocates for the creation of a national park at Yellowstone. Their cause was helped significantly by the stunning images of the area created by two members of the 1871 expedition: paintings by Thomas Moran (whose presence on the trip had been partially funded by Cooke) and photographs by William Henry Jackson (the official photographer). The U.S. Congress acted quickly to write a bill authorizing the creation of Yellowstone National Park, which was passed and signed into law by Pres. Ulysses S. Grant on March 1, 1872—unlike Yosemite, where, initially, a state park was established and only later was put under federal control.