Section M331A Yellowstone Highlands
Geomorphology. The Yellowstone Plateau was formed from two volcanic episodes. Other areas include high rugged mountains with ridges and cirques at higher elevations and narrow to broad valleys. Much of this area has been glaciated, and moraines are common. Elevation ranges from 6,000 to 13,000 ft (1,800 to 4,100 m) in the mountains, and 2,500 to 6,500 ft (763 to 1,983 m) in the basins and valleys. This Section is within the Middle Rocky Mountains physiographic province.
Lithology and Stratigraphy. Precambrian metamorphic and Tertiary volcanic rocks are in this area. Main surface flows consist of silicic rhyolites and welded tuffs. Mafic basalts rim the edge of the plateaus.
Soil Taxa. There are frigid and cryic Ochrepts, Boralfs, and Borolls, with poorly drained Fluvents, Aquolls, and Aquepts in the basins and valleys. These soils are generally shallow to moderately deep, but can be deep in valley areas. Textures are usually medium to moderately coarse with abundant rock fragments.
Potential Natural Vegetation. Kuchler mapped potential vegetation as wheatgrass--needlegrass--shrubsteppe on drier, lower elevation valleys (55 percent), and Douglas-fir forest and western spruce-fir forest (45 percent) between 5,500 and 9,500 ft (1,667 and 2,879 m). Lodgepole pine is the common cover type, with an understory of grouse whortleberry, pine grass, heartleaf arnica, or Oregongrape. Alpine vegetation, including whitebark pine and subalpine fir, occurs above 9,500 ft (2,878 m). Sheep fescue, alpine bluegrass, and American bistort are common grass and forb species.
Fauna. Birds are typical of the forested portions of the northern Rocky Mountains, including Steller's jay, black-capped chickadee, and pine siskin. This Section boasts a very rich avifauna, including such specialists as white pelican, trumpeter swan, and (black) rosy finch. Other typical species include harlequin duck, Barrow's goldeneye, Swainson's hawk, bald eagle, osprey, sage grouse, sandhill crane, Franklin's gull, American dipper, Townsend's solitaire, yellow-rumped warbler, and Brewer's sparrow. Typical herbivores and carnivores include bison, mule deer, pronghorn, elk, moose, black bear, bobcat, and cougar. Smaller common herbivores include the snowshoe hare and the northern flying squirrel. Rare species include the grizzly bear, gray wolf, wolverine, fringed myotis, pygmy shrew, pygmy rabbit, Preble's shrew, and Uinta chipmunk. Herpetofauna typical of this section are the spotted frog, prairie rattlesnake, rubber boa, boreal toad, and bloched tiger salamander.
Climate. Precipitation ranges from 20 to 45 in (510 to 1,140 mm) annually; most occurs during fall, winter and spring. It occurs mostly as snow above 6,000 ft (1,800 m). Rain is common during the growing season. Climate is cold, moist continental. Temperature averages 35 to 47 F (2 to 8 C). The growing season lasts 25 to 120 days; it is less at some higher elevations.
Surface Water Characteristics. Many perennial streams and lakes occur. Ground water supplies are small and mostly untouched. Many lakes and wet meadows are associated with areas above 6,000 ft (1,800 m). Large lakes include Yellowstone Lake, Henry's Lake, Lewis Lake, Island Park Reservoir, and Shoshone Lake. Hot springs are fairly common. Glacial valleys dominate second and higher order streams. There are many short, steep tributaries with high water and sediment delivery efficiencies.
Disturbance Regimes. Historic fire occurrence has been low intensity, low severity, patchy fires and infrequent, high intensity, high severity, continuous fires. Fire suppression has largely reversed this situation. Insect infestations and outbreaks of disease are also an important natural source of disturbance.
Land Use. Timber production and livestock grazing are the dominant land uses. A small amount of forage and other crops are grown in some valleys. The mountains are used for wildlife habitat, watershed, and recreation.
