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subsurface from the pond. If the pond becomes full, excess water flows through culverts to the drainage ditch at the base of the bluff, and then to a retention/percolation pond located north of the drainage pond. Site Geology Geology in the project vicinity consists of unconsolidated to poorly consolidated Quaternary age sediment. Holocene (Recent) levee and channel deposits of the Mokelumne River underlie the lower elevations of the site along the river, including the proposed quarry area (Wagner, et al., 1981). These deposits consist of poorly sorted sand and gravel. Prior to implementation of flood control measures, such as the Camanche Reservoir, active deposition of sands and gravels occurred in these areas on an annual basis during high runoff periods (Piper, et al., 19.19). Because of the existing flood control measures, the river would not normally flood these areas, nor would active deposition of materials occur. The bluff areas (terraces) to the south, east, and north of the project areas consist of Pleistocene sediments of the Modesto and Riverbank formations, comprised of older arkosic alluvium (Wagner, et al., 1981). Shallow borings, ranging in depth from about 25 to 40 feet, were conducted by the applicant in the area of the proposed quarry. Alluvial sediments were the only materials encountered in all but the deepest boring. This boring reportedly encountered a grey volcanic ash at a depth of about 18 feet. The nearest exposure of volcanic material is the Valley Spring formation about 4 miles east of the project near Camanche Reservoir, which contains a rhyolite tuff (Wagner, et al., 1981). Faults and Fractures No evidence has been found to indicate the presence of recently active faulting within the project area. Because no active or potentially active faults are located within the project site, the area is not considered to be subject to surface rupture from seismic activity. 19