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Eastern San Joaquin Groundwater Basin Groundwater Management Plan Northeastern San Joaquin County Section 2 Groundwater Banking Authority 40 Hydrogeology Victor The Victor Formation is of Holocene to Pleistocene Age and consists primarily of stream deposited unconsolidated gravel, sand, silt, and clay. Coarse sands and gravels are found to the east, and sands, silts and clays towards the west. This formation is generally more permeable than underlying formations, and groundwater is typically unconfined (CDM, 2001). Alluvial/Stream channel deposits Stream channel deposits are found along major stream and river courses within the study area. Generally they consist of unconsolidated gravel and coarse sand with high permeabilities (CDM, 2001). 2.2 Surface Water Features San Joaquin County lies at the northwestern corner of the San Joaquin Hydrologic Region as defined by DWR and shown on Figure 2-1. The major rivers in this hydrologic region are the San Joaquin, Cosumnes, Mokelumne, Calaveras, Stanislaus, Tuolumne, Merced, Chowchilla, and Fresno. The Calaveras, Mokelumne, and Stanislaus Rivers flow through or border San Joaquin County and at times discharge directly into the Delta or into the San Joaquin River which in turn flows to the Delta. The west and southwestern portion of the County is part of the Delta, and the areas of primary and secondary concern are shown above. The Delta and other major waterways are shown on Figure 2-2 and are discussed in more detail below (DWR, 2003). 2.2.1 Delta The Sacramento-San Joaquin Delta covers more than 738,000 acres in five counties and is comprised of numerous islands within a network of canals and natural sloughs. The Sacramento and San Joaquin Rivers come together in the Delta before they flow to the San Francisco Bay and out to the ocean. The Delta is the largest estuary on the west coast and is home to over 750 plant and animal species, many of which are threatened or endangered. The Delta provides drinking water for two-thirds of all Californians and irrigation water for over 7 million acres of highly productive farmland. Rivers in San Joaquin County all flow into the Delta as they flow out to sea. Table 2-2 provides a summary of the major reservoirs located in the region. More detailed descriptions of the rivers and the associated facilities are provided in the following sections. Table 2-2 Major Area Reservoirs River Major Reservoirs Size (acre-feet) Owning/Operating Agencies Mokelumne Pardee Reservoir Camanche Reservoir 197,950 417,120 East Bay MUD Calaveras New Hogan Lake 317,000 U.S. Army Corps of Engineers Stockton East Water District New Melones Reservoir 2,400,000 Central Valley Project Stanislaus Beardsley Reservoir Donnells Reservoir Tulloch Reservoir 77,600 56,893 68,400 Oakdale Irrigation District, South San Joaquin Irrigation District Source: State of California, California Statistical Abstract, 2002.