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deposits shed from the surrounding mountains form an alluvial wedge that thickens from the valley margins toward the axis of the structural trough. This depositional axis is below to slightly west of the series of rivers,lakes, sloughs,and marshes,which mark the current and historic axis of surface drainage in the San Joaquin Valley. The water-bearing geologic formations underlying the San Joaquin Valley typically comprise continental deposits of Late Tertiary to Quaternary age. These deposits include the Tulare Formation, older alluvium, flood basin deposits, terrace deposits, and younger alluvium. The cumulative thickness of these deposits ranges from a few hundred feet near the Coast Range foothills west of the San Joaquin Valley to about 3,000 feet along the trough east of the valley. The Tulare Formation is composed of beds, lenses, and tongues of clay, sand, and gravel that dips eastward from the Coast Range in the west towards the trough of the valley. The total thickness of the Tulare Formation is about 1,400 feet. The Coast Range sediments consist of beds,lenses,and tongues of clay, sand,and gravel, and form most of the sedimentary material deposited west of the San Joaquin River. Although there are no distinct continuous aquifers or aquitards within the Coast Range alluvium,the term"semiconfined" is used to emphasize the cumulative effect of the vertically distributed fine-grained materials. Across much of the San Joaquin Basin, a layer of older alluvium consisting of loosely to moderately compacted sand, silt and gravel deposited in alluvial fans during the Pliocene and Pleistocene ages overlies the Tulare Formation. The older alluvium is widely exposed between the Coast Range foothills and the Delta. The thickness of the older alluvium is up to about 150 feet. It is moderately to locally highly permeable. A layer of younger alluvium overlies the layer of older alluvium. This layer includes sediments deposited in the channels of active streams as well as overbank deposits and terraces of those streams. They consist of unconsolidated silt, fine to medium grained sand, and gravel. Sand and gravel zones in the younger alluvium are highly permeable and, where saturated, yield significant quantities of water to wells. The thickness of the younger alluvium near Tracy is less than 100 feet. In the northern portion of the San Joaquin Valley, flood basin deposits occur. They are the distal equivalents of the Tulare Formation and older and younger alluvial units and consist primarily of silts and clays. Occasional interbeds of gravel occur along the present waterways. Because of their fine grained nature, the flood basin deposits have low permeability and generally yield low quantities of water to wells. The flood basin deposits are generally composed of light-to-dark brown and gray clay, silt, sand, and organic materials with locally high concentrations of salts and alkali. Occasional zones of fresh water are found in the basin deposits, but they generally contain poor quality groundwater. The maximum thickness of the flood basin deposits is about 1,400 feet. Sampling and Analysis Workplan Tracy Corners Shopping Center 3225 North Tracy Boulevard Tracy,California 95376 Partner Project Number SM14-129814 Docket Number HAS-VCA 14/15-108 August 15,2016 Page 12