3.3.1.6 Shoreline and Stream Banks

frequently associated with them, soils are commonly salt-affected Aridisols (Calcigypsids or Gypsisalids). Soils along ephemeral channels are usually Entisols (Torrifluvents) on surfaces younger than approximately 6,000 years old, with wet Mollisols (Haplaquolls) occurring along streams with permanent high-water tables (Munn and Arneson 1998).

The Project vicinity is located in Soil Map Unit Zone 9: Laramie and Wind River Basins, Intermountain Basins, Frigid, aridic. Munn and Arneson (1998) define this zone as:

The Laramie and Wind River Basins are rimmed with upturned Cretaceous and older sedimentary rock. Soils developed on these parent materials are typically an association of Natrargids and Torriorthents. The interiors of the basins are filled with alluvial sediments of Tertiary and Pleistocene age. Soils on older alluvial surfaces (700,000 years and older) are usually dominated by calcium accumulations (Petrocalcids and Haplocalcids) while younger, low-relief surfaces are occupied by Haplargids (Pleistocene surfaces) or Haplocambids (Holocene surfaces). A complex of Natrargids and Haplargids occupies broad uplands developed in Tertiary-age parent materials. Riparian areas often contain Haplaquolls, and steep scarps are typically occupied by Torriorthents.

Soils in the Great Divide Basin formed in residuum or alluvium derived dominantly from shales or sandstones. Layers of both these types are often found together in alternating bands of varying thickness. Soils in the Ferris and Seminoe Mountains have a granitic base overlaid with fractured and pushed-aside uplifts of sandstone and limestone. The dark red hills bordering Seminoe Reservoir represent the Chugwater Formation. Textures range from clays to loams to sands and from very shallow to deep. Clay and silt-dominated soils are often saline or alkaline, while sandy and loamy soils have had enough precipitation to leach salts sufficiently to allow them to function (effective rooting depth) as moderate to deep soils. Soils in the North Platte River Basin are generally sands and sandy clay-loams, with gravel and rocks becoming more numerous closer to the mountains and along higher gradient streams (BLM 2003).

3.3.1.6 Shoreline and Stream Banks Reservoirs

The proposed upper reservoir will be constructed to the west of the Bennett Mountains Wilderness Study Area (WSA) in an unwooded area that has a minimum existing ground elevation of approximately 7,280 feet. The area of the proposed upper reservoir is situated in Precambrian (late Archean) rocks of the Seminoe Mountain core located on a flat-topped granite mountain. Vegetation in the area of the proposed upper reservoir includes mostly herbaceous vegetation with scattered shrubs.

The shoreline of the lower reservoir within the Project vicinity is dominated by steep bedrock cliffs with occasional large boulder and bedrock shard complexes which extend deep into the lower reservoir. Shoreline slopes in this area of the lower reservoir generally range from vertical to near vertical. Other portions of Seminoe Reservoir in the Project vicinity are also dominated by steep shores with occasional vertical cliffs intermixed with areas of moderate to gentle slopes along the shoreline. Farther east from the Project vicinity within Seminoe Reservoir, many portions of the shoreline are dominated by sand,