ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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4.8 PALEONTOLOGICAL RESOURCES Paleontological resources (fossils) are the remains or traces of prehistoric animals and plants. This section assesses the potential for earthmoving activities associated with development in the project area to adversely affect scientifically important fossil remains. The analysis presented in this section conforms to Society of Vertebrate Paleontology criteria. This analysis includes a description of the local geologic setting,the impacts associated with implementation of the proposed project,and any recommended measures to mitigate the project's potential impacts. 4.8.1 ENVIRONMENTAL SETTING GEOGRAPHIC LOCATION AND PHYSIOGRAPHIC ENVIRONMENT The project area is located in the Great Valley Geomorphic Province of California, a large northwest-trending valley bounded by the Sierra Nevada to the east and south,the Coast Ranges to the west, and the Klamath Mountains to the north. The Great Valley is drained by the Sacramento and San Joaquin Rivers,which join and flow out of the province through the San Francisco Bay. This geomorphic province is an asymmetric trough approximately 400 miles long and 50 miles wide filled with a thick sequence of sediments ranging from Jurassic (180 million years ago)to Recent age. The sediments in the Great Valley vary between 5 and 10 kilometers in thickness and were derived primarily from erosion of the Sierra Nevada to the east,with lesser amounts of material from the Coast Ranges to the west. For additional information on geographic location and physiographic setting, see Section 4.7, "Geology, Soils, and Seismicity." REGIONAL AND LOCAL GEOLOGIC SETTING Geology of the San Joaquin Valley has been described in some detail by authors such as Bartow(1991), Graham and Olson(1988),Page(1986), and Bailey(1966), among others. Geologic history and conditions are relevant to the evaluation of paleontological resources in that they influence the type of fossils that may be found (i.e., aquatic vs. terrestrial organisms)and the probability that any prehistoric remains would be subject to fossilization rather than normal decay. The depositional history of the upper San Joaquin Valley during the Quaternary period(approximately 1.8 million years Before Present [B.P.])included several cycles related to fluctuations in regional and global climate that caused periods of deposition along the valley floor alternating with periods of subsidence and erosion. By the middle of the Pleistocene epoch(approximately 900,000 years B.P.), the seaway serving as a drainage outlet connecting the San Joaquin Valley with the Pacific Ocean had closed, leaving behind a large lake(the Corcoran lake)in the Central Valley. Meanwhile, continued uplift of the Sierra Nevada resulted in ongoing sediment deposition along the valley floor. Thus,the project region during the Pleistocene epoch consisted of stages of wetland and floodplain creation as tidewaters rose in the valley from the west, areas of erosion when tidewaters receded, deposition of alluvial fans that were reworked by wind to create extensive sand dunes, and alluvial fan deposition from streams emanating from the adjacent mountain ranges (Bartow 1991,Atwater 1982). The proposed improvements at the wastewater quality control facility(WQCF),pipeline alignments for the proposed collection system and recycled-water distribution system, outfall pipeline, side-bank outfall structure, and pumping station sites span the U.S. Geological Survey(USGS)Manteca and Lathrop 7.5-minute quadrangles, and are underlain by Dune Sand and the Modesto Formation,which are described in greater detail below. Manteca WQCF and Collection System Master Plans EIR EDAW City of Manteca 4.8-1 Paleontological Resources