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Erosion and Sediment - Field observations indicate that the average annual erosion rate on 30 percent of the study area is in excess of five tons-per-acre-per-year. Streambank erosion in excess of 1,000 tons per mile occurs on about ten percent of the stream channels. The badlands within the area are rapidly eroding and are major contributors of both salts and sediments to irrigated land and water resources. Much of the badlands have developed in the Muddy Creek For- mation which is made up of clay, silt and sand and also contains much salt and gypsum. As shown in the geologic section (Figure 4-B) there is and abundance of limestone, gypsum and salt in other strata ex- posed to the forces of geologic erosion which also contribute to the salinity of Muddy River. Geologic erosion of these formations is not economically feasible to control. This erosion will continue with or without implemen- tation of the program plan. Biotic Resources The study area has a highly diversified environment consisting of a variety of biotic communities. Vegetation zones forming a basis for recog- nition of biotic communities are: Creosote Brus h Bl ackbrush Saltbrush Desert Ri pari an Distribution of biota in terms of the numbers of species of vascular plants, fish, amphibians, reptiles, birds and mammels is given in Appendix C. Riparian and Cliff Desert Springs and Marsh Streamside and Riparian Numerous species of macroinvertibrates exist but investigations have not been conducted to identify them and the effects of varying flows and sa 11 ni ty. Fisheries - Species endemic to the Muddy River belong to two families cyprinidae (minnows and carp) and cyprinodontidae (killifishes). Four endemic and eight exogenous species of fish have been identified in the study area. Nevada Wildlife Commission has listed two of the endemic species, the White River Spring Fish and the Moapa Dace, as "rare", as of February 1, 1979. However, only the Moapa Dace is listed as a threatened species by U. S. Fish and Wildlife Service. Species are listed in Appendix C. Wildlife - A total of 169 species of birds have been identified in Moapa Valley Subevaluation Unit. This includes species classified as breeding in the area, transients or winter residents as well as those shown as accidental sightings. Data on birds is from a list of Clark County avifauna presented by Austin and Bradley (1971) and modified by information provided by Johnson (1973), Lawson (1972), Ryser (1970) and records on file with the Nevada Department of Wildlife. A list of ninety-three species of mammals (12 nonconfirmed and 2 feral) found in the study unit was compiled from information presented by Deming (1963), Hall (l946), Ryser (N.D.), and records of the Nevada Department of Wildlife. 21 ,.....' '''l C/ ..... J.