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i APPENDIX A- Historical Background SUTTER OFFICE CENTER ' SITE LOCATION The site is located in a commercial area of low topographic relief in central Stockton, California There is one multistory building (242 North Sutter Street) occupied by multiple businesses on the ' western portion of the site, the remaining portion consists of paved parking REGIONAL GEOLOGIC/HYDROGEOLOGIC SETTING e The site is situated within the southern portion of the Great Valley Geomorphic Province of California, a large, elongate, northwest trending, asymmetric structural trough, the northern and southern portions of the Province have been designated the Sacramento and San Joaquin Valleys, respectively The Province is bordered by the Coast Ranges to the west,the Klamath Mountains and Cascade Range to the north, and the Sierra Nevada to the east The Great Valley has been filled with sediments derived from both marine and continental sources Thickness of the sedimentary fill ranges from thin veneers along the valley edges to more than 20,000 feet in the south central portion of the valley The sedimentary formations range in age from Jurassic to Recent,with the older deposits being primarily marine in origin and the younger deposits being primarily continental Continental-denved sediments were prunanly deposited in lacustrine, fluvial,and alluvial environments with sediment sources being the mountain ranges surrounding the valley(Olmsted and Davis, 1961),the site itself is located on unconsolidated and semi-consolidated alluvium, lake, playa and terrace deposits of Quaternary age (California Division of Mines and Geology, 1977) Rocks composing the basement complex of the Province have not been completely defined but are believed to be metamorphic and igneous in origin The Modesto Riverbank and Turlock Lake Formations and overlying Recent alluvium are the I principal sources of domestic ground water in the 13,500-square mile San Joaquin Valley Ground Water Basin (Basin 5-22) Based on review of the Lines of Equal Depth to Groundwater Sprang 1999 map published by the San Joaquin County Flood Control District and Water Conservation District(FCD&WCD),the estimated depth to ground water at the site to be 30 feet bsg Review of the map Lanes of Equal Elevation of Groundwater Spring 1998(FCD&WCD) depicts the regional ground water flow direction towards the northwest and west Review of previous ground water monitoring at the site and historical depth to ground water maps(FCD&WCD)dating back to 1971 suggests that ground water depth near the site has fluctuated between 50 feet bsg and 60 feet bsg