Section M332E Beaverhead Mountains
Geomorphology. This area encompasses complex and high, steep mountains with sharp alpine ridges and cirques at higher elevations, glacial and fluvial valleys, and alluvial terraces and flood plains. Elevation ranges from 2,500 to 6,500 ft (763 to 1,983 m) in valleys; elevation ranges from 4,000 to 10,000 ft (1,220 to 3,050 m) in the mountains. This Section is within the Northern Rocky Mountains physiographic province.
Lithology and Stratigraphy. Composition is complex, including Precambrian granitic, Paleozoic metamorphic, and Tertiary sedimentary and volcanic rocks.
Soil Taxa. Soils include frigid and cryic Ochrepts, Boralfs, and Borolls, with some Fluvents and Aquepts in alluvial valleys. Mountain soils are generally shallow to moderately deep and have loamy to sandy textures with rock fragments. Valley soils are moderately deep to deep and have loamy to clayey textures.
Potential Natural Vegetation. Vegetation consists of sagebrush steppe with small areas of alpine vegetation (75 percent) above 9,500 ft (2,880 m), and Douglas-fir forest (25 percent) the latter spans an elevation range of only about 1,000 to 1,500 ft (300 to 450). Typical steppe species include big sagebrush, fescues, wheatgrasses, and needlegrass. Douglas-fir, limber pine, and lodgepole pine are common tree species.
Fauna. Birds are similar to those in M332B, with a larger number of species typical of the Great Plains. Species of note are trumpeter swan, Barrow's goldeneye, Swainson's hawk, golden eagle, sage grouse, sandhill crane, American dipper, Townsend's solitaire, and Brewer's sparrow. Birds nearing the edge of their range are spruce grouse, black-throated hummingbird, pileated woodpecker, eastern kingbird, red-eyed vireo, and northern water thrush. Typical herbivores and carnivores include white-tailed deer, mule deer, pronghorn, elk, moose, black bear, bobcat, and cougar. Smaller common herbivores include the snowshoe hare and northern flying squirrel. Rare species include the gray wolf, lynx, wolverine, pygmy rabbit, Great Basin pocket mouse, and the northern bog lemming. Herpetofauna typical of this Section are the spotted frog, wood frog, Pacific treefrog, boreal toad, western toad, and long-toed salamander.
Climate. Precipitation ranges from 10 to 50 in (250 to 1,270 mm). Most fall, winter, and spring precipitation is snow. Winters are cold, and growing season conditions are dry. Soil moisture is not sufficient for tree growth on some south and west aspects below timberline; hence, grasslands often extend from the valley floors to the mountain tops. Climate is cold dry continental. Temperature averages 36 to 46 ºF (2 to 8 ºC). The growing season ranges from 45 to 100 days.
Surface Water Characteristics. Drainage patterns are complex, reflecting the complex geology. Intermittent drainages are common, indicating the somewhat arid nature of the area. Lakes occur in glaciated areas at higher elevations. Major rivers include the Lemhi, Beaverhead, and Ruby.
Disturbance Regimes. Fire, insects, and disease are the principal natural sources of disturbance.
Land Use. Livestock grazing is the dominant land use. Limited timber harvesting, mining, wildlife habitat, and recreation are also important land uses.
