temblors centered in the park’s northwest sector in 2004 sparked renewed speculation about the possibility of another gigantic volcanic event and the possible resulting global climate disruption. Volcanologists downplay the possibility of such an event in our lifetime. However, some say its likelihood is 5 to 10 times greater than that of a globally destructive asteroid impact.
Boardwalks provide close access to many frontcountry hot springs.
Also related to the hot spot are Yellowstone’s unique, super-heated hydrothermal features. A recent inventory conducted by the Yellowstone Center for Resources estimates that the park is home to more than 18,000 distinct geothermal features. The most common surface expressions of the park’s extensive subterranean plumbing network are hot springs, where colorful thermophiles (heat-loving microorganisms, also known as extremophiles) and cyanobacteria (single-celled photosynthetic bacteria) thrive in pools of geothermally heated water. These springs are often linked to geysers (from the Icelandic word geysir, which means “to gush or rage”), where highly pressurized water rockets toward the surface and often flashes to steam. Fumaroles are dry, hissing vents that issue hydrogen sulfide (the source of that “rotten egg” odor), hydrochloric acid, and other gases. A solfatara is a sulfur-emitting fumarole. Mud pots (also known as paint pots when tinted by minerals) form in thermal areas where precipitation mixes with fine volcanic soils to create a bubbling, viscous—and often very acidic—slurry, sometimes forming mud volcanoes.
For hikers, this ancient ice sculpting and geothermal hyperactivity translates into many unusual geologic features to explore, including multilayered fossil forests, lava flows, dramatic U-shaped canyons, glacial boulder fields, and black mountains of obsidian. These varied and dramatic landscapes form numerous ecological niches that support an amazing diversity of wildlife and plants, many of them reachable only on foot.
Flora
Some 1,100 native species of flowering plants are found in Yellowstone alone, but only three species are endemic: the Yellowstone sand verbena, the Yellowstone sulfur wild buckwheat, and Ross’s bentgrass. There are more than 200 nonnative species, some of which are starting to invade the backcountry. An additional 600 species of fungi, lichens, mosses, and liverworts have been cataloged. It’s legal to collect small quantities of edible plants and berries for personal consumption, but keep it to a minimum to maintain your good bear karma.
Elevation has the most influence over which plant species flourish where. Though the vegetation varies significantly throughout the ecosystem, it’s mostly typical of the Rocky Mountains. The observant hiker may notice elements of seven distinct biomes from the surrounding deserts, plains, montane forests, and arctic tundra.
Thanks to their shallow root systems, vast tracts of drought-tolerant lodge-pole pines dominate the nutrient-poor, volcanic soils within the Yellowstone Caldera. In sharp contrast, the clayey glacial lake beds beyond the caldera encourage a much more diverse flora.
Botanists group Rocky Mountain vegetation into five zones: foothills, riparian, montane, subalpine, and alpine. These zones overlap considerably and are not strictly defined. The altitude and width of each zone increase progressively as you move from north to south. Fall colors peak around the autumnal equinox (third week in September) in the Tetons, a bit later on Yellowstone’s relatively low-lying Northern Range.
Most of Yellowstone’s lower-elevation hikes begin in sagebrush-blanketed foothills (5,500–6,500 feet). A prime example of this type of habitat is the arid Northern Range, where the annual precipitation hovers around 20 inches. The lower elevations here make the region a preferred spring and fall hiking destination. Unique species found here include cacti and Rocky Mountain juniper. In the absence of foothills in the Tetons, most trails begin near Jackson Hole and the Snake River Plain, where porous soils support sagebrush, grasses, and numerous wildflowers.
Riparian or wetland communities prosper near year-round streams. Typical moisture-loving plants in this zone include rushes; sedges; colorful deciduous trees such as cottonwoods; and shrubs such as willow, quaking aspen, dogwood, mountain ash, and Rocky Mountain maple. These lush but narrow areas are often home to rare, water-loving wildflowers and provide a transition between aquatic and upland steppe environments. North-facing slopes, which receive less sunlight and thus retain more moisture, are favored by most plants. Several rare aquatic plants thrive in Yellowstone’s hydrothermal areas, such as the Shoshone Geyser Basin.
Semiarid steppe vegetation is primarily scrubby and is dotted by lots of fragrant Big Mountain sagebrush, open woodlands, and more than a hundred species of sparse grasses. Prime, wildlife-rich examples of this habitat occur in Yellowstone’s Hayden Valley, Pelican Valley, and Swan Lake Flats. Conspicuous blooms of wildflowers such as the pungent yellow arrowleaf balsamroot; snow-white, mat-forming phlox; flaming scarlet-orange Indian paintbrush; and pastel lupines and penstemons festoon hillsides in late June and early July.
Aspen grove near Taggart Lake (Trail 35)
Sagebrush-interspersed meadows mark the transition between rolling prairies and the forested montane zone (6,000–9,500 feet). Snow persists at higher elevations until July or August around the highest passes. The resulting short, cool growing season limits the number of plant species. Snowmelt on warmer, south-facing slopes waters hearty conifer (cone-bearing) species, such as Douglas-fir; Englemann spruce, which dominates older forests; and the higher-ranging subalpine fir. Shrubs and berries dominate the damp under-story. If there is a prolonged absence of fire, spruce–fir forests should begin to succeed the currently dominant lodgepole stands.
Subalpine habitat below Rendezvous Mountain in the Teton Range (Trail 42)
Beyond the upper montane zone, the wild subalpine zone (7,500–10,000 feet) continues up to timberline. Isolated spruce–fir stands dominate where snow lingers longest. Short-lived wildflower displays can be fantastic after the spring snowmelt. At higher elevations, such as around Mount Washburn, the nuts of whitebark pine (which is sometimes confused with limber pine) are a favored but erratic source of prehibernation nutrition for ravenous grizzly bears.
Above timberline, the alpine zone (above 9,000–10,000 feet) is reserved for the most robust species of both plants and humans. The exposed meadows and rocky outcrops host bountiful but short-lived wildflower shows in late July and August. Wind-stunted Krummholz trees abide in sheltered areas of southern exposure. More than 200 plant species have been cataloged just beyond Yellowstone’s Northeast Entrance on the untamed Beartooth Plateau, one of the largest swaths of alpine tundra in the Lower 48.
Fauna
Let’s face it: geyser gazing and rambling around alpine peaks aside, a trip to Yellowstone and the Tetons isn’t complete without spotting—and photographing—a root-grubbing bear with her cute yearling cub, a bugling eight-point elk, a drooling moose, or, at the very least, a wallowing bison.
Besides the iconic thermal features that earned Yellowstone its early nickname “Wonderland,” the park’s photogenic wildlife is the main draw for most visitors. Thanks to the successful wolf-reintroduction effort (see page 10), Greater Yellowstone now supports all of the 61 native mammal species it has historically hosted. With such an incredible concentration of charismatic megafauna, these parks are easily among the world’s foremost wildlife-watching hot spots.
The comparison frequently drawn
