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2.0 GEOLOGY AND HYDROGEOLOGY 2.1 REGIONAL GEOLOGY The Central Valley and surrounding area is the product of a complex series of geologic events. The Sacramento Valley is a late Mesozoic forearc basin that formed contemporaneously with, and between the accretionary trench deposits of the Franciscan Complex to the west, and an eastern magmatic are complex, the roots of which are exposed in the Sierra Nevada Mountains. The region has experienced orogenic uplift, faulting, and subsequent erosion as the valley was inundated by the ancestral Pacific Ocean. The exposed granite of the Sierra Nevada mountain range represents the eroded edge of a tilted block of crystalline rocks known as the Sierra Nevada Batholith. The Sierra Nevada Batholith is a series of granitic plutons that range in age from Jurassic to Cretaceous. The plutons intruded sedimentary and volcanic rocks of Ordovician to Late Jurassic age. The Sierra Nevada Mountains locally are the bedrock upon which the Great Valley sequence rests, in other locations, mudflows and lahars of the Pliocene Tuscan Formation and younger volcanics rocks cover the granitic bedrock, which plunges beneath the Great Valley sequence at the eastern margin of the Central Valley. The Great Valley sequence is a very thick accumulation of sediments forming an asymmetric structural trough or syncline, with the axis of the trough west of the apparent surface axis of the present valley surface. The trough has been filled with as much as 10 vertical miles of sediment in the Sacramento Valley (the Great Valley Sequence), and these sediments range in age from Jurassic to Holocene. The Great Valley sequence rests on basement rocks consisting of metamorphosed sedimentary and volcanic rocks of Ordovician to Late Jurassic age. 2.2 REGIONAL HYDROGEOLOGY The subject site is located in the Eastern San Joaquin County Groundwater Basin, an area covering approximately 707,000 acres (1,105 square miles). The San Joaquin Valley comprises the southernmost portion of the Great Valley Geomorphic Province of California. The Great Valley is a broad structural trough bounded by the tilted block of the Sierra Nevada on the east and the complexly folded and faulted Coast Ranges on the west. The Eastern San Joaquin Subbasin is defined by the areal extent of the unconsolidated to semi consolidated sedimentary deposits that are bound by the Mokelumne River on the north and northwest; San Joaquin River on the west; Stanislaus River on the south; and consolidated bedrock on the east. 12/22/2009 HANOVER ENVIRONMENTAL SERVICES, INC. 2 Soil Assessment Report McHenry Ave Project 1303 First Street, Escalon