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Section 342A  Bighorn Basin

Geomorphology. There are piedmont plains and mountain footslopes with large stream terraces along the Wind-Bighorn River system. Plains are eroded to clay shale bedrock in some places, forming badlands. Elevation ranges from 3,600 to 5,900 ft (1,100 to 1,800 m). This Section is within the Middle Rocky Mountains physiographic province.

Lithology and Stratigraphy. Oligocene, Eocene, and Paleocene sedimentary rocks overlie Precambrian rocks.

Soil Taxa. Types include mesic Argids, Orthids, and Orthents. These soils are generally moderately deep to deep with moderately fine to clayey textures.

Potential Natural Vegetation. Kuchler classified potential vegetation as saltbush-greasewood, wheatgrass-needlegrass-shrubsteppe, and sagebrush steppe. Common species include big sagebrush, gardner saltbush, indian ricegrass, and needleandthread. Black sage and bluebunch wheatgrass are common on areas with shallow soils.

Fauna. Birds are typical of the middle Rocky Mountains, and are very similar to those that occur in Sections M331A and M331B. Other species of note are the ferruginous hawk, golden eagle, sage grouse, burrowing owl, Say's phoebe, sage thrasher, and pygmy nuthatch. Eastern kingbirds near the edge of their range in this Section. Typical herbivores and carnivores include white-tailed deer, mule deer, pronghorn, bobcat, and cougar. Smaller common herbivores are the white-tailed jackrabbit, white-tailed prairie dog, and black-tailed prairie dog. Less common is the black-tailed jackrabbit. The bison and black-footed ferret 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 averages 5 to 9 in. (120 to 230 mm). Temperature averages 45 F (7 C). The growing season lasts 120 to 140 days.

Surface Water Characteristics. There are moderate to deeply incised third to fifth order streams with dendritic drainage patterns. Major rivers include the Wind, Bighorn, Greybull, and Shoshone. Deep artesian wells also occur.

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

Land Use. The dominant land use is livestock grazing. About 5 percent of the area is irrigated.