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Geotechnical Engineering Investigation Page 4 of 24 <br /> New Residential Subdivision <br /> 2706 Pock Lane <br /> Stockton, CA 95205 <br /> March 30, 2021 CTE Job # 25-1097G <br /> 4.0 GEOLOGY <br /> 4.1 General Geologic Setting <br /> The site is located in the central area of the San Joaquin Valley. The San Joaquin Valley is located <br /> within the Great Valley Geomorphic province in California. The Great Valley Geomorphic <br /> province is an alluvial plain in which sediments have been deposited nearly continuously since the <br /> Jurassic. The gently sloping, eastern alluvial fans are principally composed of deposits from <br /> granitic rock sources in the Sierra Nevada. The smaller,more steeply sloping fans on the west have <br /> originated from sedimentary and metamorphic rocks of the Coast Range (Davis et al., 1959). <br /> The San Joaquin Valley has been filled with hundreds of feet of erosional sediments, ranging in <br /> age from Pleistocene to Holocene. Recent alluvial deposits generally consist of poorly sorted silts <br /> and fine sands with less extensive lenses of medium to coarse grained sands and gravel. Lacustrine <br /> deposits occur along the axis of the valley,and consist of clays, silts,and fine sands. These alluvial <br /> units overlie Pliocene-Pleistocene continental clastic deposits, which in turn lie over older <br /> continental and marine deposits. A pre-Tertiary basement complex of granitic and metamorphic <br /> rocks uncomfortably underlies the entire area. <br /> Based on geologic reconaissance and observations made within the test borings, alluvial materials <br /> encountered during the investigation were considered to be consistent with Quaternary(Holocene) <br /> Modesto Formation deposits as shown on published regional geologic mapping"Geologic Map of <br /> the San Francisco-San Jose Quadrangle, California" (CDMG Regional Geologic Map 5A, Scale <br /> 1:250,000, 1991). The mapped area shows one surficial geological unit, Holocene Modesto <br /> Formation(Qm). <br /> 4.2 Generalized Soil Conditions <br /> Soil materials encountered in our site explorations are consistent with the above referenced <br /> published geologic mapping. The native alluvial deposits encountered generally consisted of very <br /> stiff to hard sandy clays (CL) underlain by approximately 2 feet of hard sandy low plastic silts <br />