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). H. KLEINFELDER & ASSOCIATES <br /> File No. S-1008-35 <br /> May 17, 1985 <br /> Page 6 <br /> greater. In the past, the Foothills fault system has been considered inactive, with no <br /> !mown creep or displacement of geologic features since Late Tertiary time. On August 1, <br /> 1975, an earthquake of magnitude 5.7 occurred approximately 6 miles southeast of Oroville. <br /> As a result of this event and subsequent aftershocks, a reevaluation of the potential activity <br /> of the Foothills fault system took place. It has been proposed that a 6.5 magnitude <br /> earthquake may occur almost anywhere in the Foothills fault system. <br /> The reevaluation of the Foothills fault system consisted, in part, of trenching across <br /> known lineaments of the Bear Mountains and Melones faults. Trenches excavated in the <br /> vicinity of Rawhide Flat, near Sonora, California, indicate offset within the older soil <br /> horizons. Additional trenching in areas to the north indicate possible offset of the <br /> Mao-Pliocene Mehrten Formation by the Hear Mountains fault. <br /> Using methods derived by H. Holton Seed and 1. M. Idriss, Table I, below, was <br /> compiled for bedrock accelerations to be expected in the site area. <br />