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particular attention to sensitive or unique of their high habitat values. Almost three vegetative communities capable of provid- linear miles of valley riparian scrub occur in ing sufficient wildlife values. a band,20-30 feet in average width, along the southwestern bank of Old River. The Most of the land in the study area is culti- mixed riparian herb/scrub community along vated land. Non-irrigated lands are used to this shore contains vegetation which adapts produce annual crops of hay and pasture for quickly to the disturbances caused by levee livestock. Irrigated lands produce a range maintenance and farming practices which of row crops such as sugar beets and has for the most part prevented the develop- livestock feed such as alfalfa. Because ment of mature riparian forests. these lands are generally intensively man- aged to provide maximum yields of the Although no rare or endangered wildlife desired crop,very little development of species are known to reside on the study volunteer vegetation is permitted to occur. area and none were observed during the Farming to the fence lines and to the banks biological survey, the existing habitats, of most remaining wetlands and riparian though heavily damaged by human activi- habitats as well as the use of herbicides and ties,may provide sufficient isolated areas pesticides effectively eliminates most wherein one or more listed birds,mammals, unwanted vegetation and greatly reduces amphibians or insects might exist. Detailed any wildlife values these lands might surveys will be conducted for any candidate otherwise provide. Only where acreage has or listed wildlife species for which suitable been permitted to lie fallow for periods of habitat is present or which is suspected to time are any wildlife values available. exist within the proposed project bounda- ries. The extreme western margin of the study area,near the Mendota Canal, contains non- Soils and Geology: native grasslands dominated by wild oats, bromes and chesses, filarees, and vetches The most extensive soil group on the site mostly of mediterranean origin. Freshwater consists of the clays and clay loams of the marshes exist along most of the waterway gently sloping to rolling terraces, as shown created by Mountain House Creek and some on Figure 6. A narrow strip of flatland irrigation channels, around several artificial clays and loams occurs along the Old River. ponds, on the unnamed creek which empties Older alluvial soils (adobe clays)occupy the into Old River near Hammer Island and terraces along Mountain House Creek. along backwaters where Mountain House Adobe clays developed thinly over bedrock Creek empties into Old River and along the occur in the ridges along the Delta-Mendota west side of Wicklund Road. Though Canal. limited in extent within the study area, these wetland communities are important because Site Description 3.3