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' Terrace deposits of Pleistocene age, up to several hundred feet higher than present <br /> stream beds, are present in the study area at the mouth of Corral Hollow Creek as it <br /> ' leaves the Coast Range. These deposits are similar to the coarser grained deposits of <br /> the underlying Tulare Formation. <br /> ' Alluvium of Pleistocene and Holocene age is composed of interbedded, - <br /> g p e bedded,poorly to well- <br /> ' sorted clay, silt, sand, quid gravel and is lithologically similar to the underlying Tulare <br /> Formation. The contact between the two is indistinguishable in drill holes. <br /> ' 2.3.3 Site Geology <br /> ' The exploratory drilling program at the Corral Hollow Sanitary Landfill shows that the <br /> site is underlain by semiconsolidated and unconsolidated deposits of Tertiary and <br /> ' Quaternary age. The position of the Corcoran Clay Member which was found at a <br /> shallow depth, indicates that the majority of the sediments underlying the site belong to <br /> ' the Tulare Formation; the remainder are Quaternary. The alluvial deposits in the study <br /> area are heterogeneous mixtures of coarse-grained sands and gravels with variable <br /> proportions of fine sands, silts, and clays. These sediments are products of the erosion <br /> of deposits located hi the adjacent highlands, transported by a combination of gravity <br /> and stream action, and deposited in large fan shaped masses at the base of the <br /> ' highlands.The materials have been deposited into near horizontal units differentiated by <br /> changes in lithology, texture, and hydraulic properties. <br /> The coarse-grained alluvial deposits encountered in borings at the site are separated by a <br /> clayey unit, interpreted as the Corcoran Clay Member of the Tulare Formation. (see <br /> Drawings 2 and 3). <br /> The Corcoran Clay in the study area consists of interbedded sandy silts, sandy clays, <br /> and silty clays. The unit, is approximately 50 feet thick beneath the east side of the <br /> ' facility,thins rapidly across the landfill and pinches out into the underlying clayey sands <br /> and clayey gravels near the western edge of the landfill (see Drawing 3). The Corcoran <br /> ' Clay is considerably coarser grained in the study area than typically recorded toward the <br /> valley (Hotchkiss, 1972). This suggests that the sediments were deposited into the <br /> ' distal portion of a lacustrine environment, closer to the source area for the sediments. <br /> STL 9390314 7 Rev. 0 06/30/88 <br /> ' Emcon Associates <br />