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E November 1990 -b- M881&8D REGIONAL GEOLOGIC CONDITIONS _ The site is located in the Great Valley geomorphic province of Central. California. The Great Valley is an elongate lowland which exist between the Sierra Nevada and Coast Ranges, and rises from slightly below sea level to approximately 400 feet at both its north and south ends (Norris & Webb, 1990, p, 412). The valley is unusual for a lowland because it is a relatively undeformed basin surrounded by highly deformed rock units. The Sacramento Rives drains the j northern portion and the San Joaquin River the southern part. The lowland is also referred to as the Central galley, its northern segment as the Sacramento 3 Valley, and its southern segment as the San Joaquin Valley (Norris & Webb, 1990, .. s p. 412). The surface of the Central Valley is composed of unconsolidated i Quaternary sediments, which are underlain by approximately 12,000 feet of Quaternary- and Tertiary-aged alluvial deposits. Sierra Nevada Basement material j exist beneath the alluvial deposits at depths ranging from 10,000 to 30;000 feet Y, (Norris & Webb, 1990, p. 418-419). -5179 GEGLOGY m The subsurface geology.underlying the site is Quaternary alluvium — F predominantly composed of alluvial fan deposits. There are no faults mapped near 'r� 1 the property. The Midland fault zone is concealed by alluvium but is mapped b w y inference to lie approximately 20 miles west of the site, a EARTH MATERIALS Alluvium (Qal). Alluvium material was encountered in each of the A 1 four borings at grade and extended to the total depths of each (up to 90 feet bgs �4 at DH-2). This material consisted of moderate brow-n to dark yellowish brown, loose to very zdense, dry to very moist, interbedded sand (SP), silty sand (SM),r and clayey sand (SC). The locations of the various earth materials encountered during the assessment are shown on Plates A-1.1 through A-1,4 - Log of Monitoring fi - .�� 4 �F � I