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Section 331G  Powder River Basin

Geomorphology. This area includes gently rolling to steep dissected plains on the Missouri Plateau. Wide belts of steeply sloping badlands border a few of the larger river valleys. In places, flat-topped, steep-sided buttes rise sharply above the surrounding plains. Elevation ranges from 3,000 to 6,000 ft (915 to 1,830 m). This Section is within the Great Plains physiographic province.

Lithology and Stratigraphy. There are Cretaceous and Lower Tertiary non-marine sedimentary rocks. Glacial lake beds also occur.

Soil Taxa. Soils include Orthents, Orthids, Argids, Borolls, and Fluvents. Temperature regimes are generally frigid in the north and mesic in the south. These soils are mostly medium to fine texured and range from shallow to deep.

Potential Natural Vegetation. Kuchler mapped vegetation as grama-needlegrass-wheatgrass. About 20 percent of the area supports eastern ponderosa forest. Dominant grassland species include western wheatgrass, blue grama, green needlegrass, bluebunch wheatgrass, and needleandthread. Little bluestem replaces bluebunch wheatgrass in the eastern part of the Section. Basin wild rye and sagebrush occur along streams and on bottomlands.

Fauna. Typical birds are sagebrush obligates or specialists, such as sage grouse, sage thrasher, and sage and Brewer's sparrows; sage thrasher and sage sparrow near the edge of their ranges in this Section. Other specialists are ferruginous and Swainson's hawks, golden eagle, Say's phoebe, and McCown's longspur. Typical riparian species include Lewis' woodpecker, yellow warbler, and lazuli buntings. Several bird species that reach or nearly reach the extent of their ranges in this Section are eastern screech-owl, red-headed woodpecker, Cassin's kingbird, pinyon jay, green-tailed towhee, and clay-colored sparrow. Typical herbivores and carnivores include white-tailed deer, mule deer, pronghorn, bobcat, and cougar. Smaller common herbivores include the white-tailed jackrabbit, white-tailed prairie dog, and black-tailed prairie dog. Less common is the black-tailed jackrabbit. The black-footed ferret is a rare species within this Section. Bison are historically associated with this Section. Herpetofauna typical of this Section are the Great Plains toad, snapping turtle, spiney softshell turtle, smooth green snake and prairie rattlesnake.

Climate. Precipitation ranges from 10 to 20 in (250 to 510 mm), most of which falls as spring and summer rain. Winter precipitation is snow. Climate is cold continental with dry winters and warm summers. Temperature averages 39 to 45 F (4 to 7 C). The growing season lasts 120 to 140 days.

Surface Water Characteristics. Low to medium density drainages occur on more permeable surfaces. Large, shallow head basins underlain by coal or scoria are water collection areas. Much of the drainage pattern is structurally controlled. Major rivers include the Yellowstone, Tongue, and Powder.

Disturbance Regimes. Fire and drought are the principal natural sources of disturbance.

Land Use. Livestock grazing is the dominant land use; a small amount of dryland farming also occurs.