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4.7 BIOLOGICAL RESOURCES A sparse shoreline riparian vegetation, consisting primarily of scattered willows, persists under heavy cattle grazing. The Mokelumne River is one of the many Sierra foothill waterways whose present flow is controlled by water releases from foothill reservoirs. Water level and flow rate varied greatly during the 10-month study period (Figure 4.7-7). Much of the shoreline vegetation present in late summer is temporally covered by high flows during the rainy season, then reappears and rejuvenates during the following dry season. The Mokelumne River also helps to maintain the woodland riparian area by periodically overflowing its banks. While this occurs on a limited basis, nonetheless, such overflows are of a magnitude to help restock the Beaver Pond with fish such as what occurred during the 1986 flood. Its passage along the presently undisturbed riparian frontage of the project site provides viewers with one of the last glimpses of what the majority of foothill stream riparian zones once looked like in San Joaquin County. Seasonal Wetlands Seven vernal pool sites held water throughout the late winter and the early 1992 spring period (Figures 4.7-1 and 4.7-8). Vernal pools are small, seasonal wetlands that form in a shallow depression in relatively level terrain due to the lack of rainfall percolation through an impervious soil layer. As the winter rains subside and temperatures increase throughout spring,the pool water continuously evaporates, leaving a zone of moist ground immediately surrounding the remaining water. This creates an ever- changing set of miniature habitats for highly specialized plant and animal species that thrive during this brief spring period and then die, leaving behind drought resistant seeds and eggs which will renew the cycle in the following year. Many of these species are found only in such vernal pool habitats, and since the majority of these habitats in California have been destroyed by agriculture and grazing, a number of such species are now classified as threatened or endangered. The dominant vernal pool plant species on the project site is Eryngium vaseyi. Also present is Plagiobothrys stipitatus and Limnanthes douglasii. None of these species have common names. As the pools dried, hydrophilic species present in other wet areas on the project site appeared within the pool margins. These included a small sedge species (Carex sp.) and curly dock (Rumex crispus). None of the species identified in the vernal pool basins are listed under any protective categories by either the California Native Plant Society or the California Department of Fish and Game. 4.7-7