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GI Y17~ -- i N c o a voa ~ r= o IV. SITE GEOLOGY A geologic map prepared by Berlogar Geotechnical Consultants (BGC) (Plate 4, 1990) shows __ limits of bedrock and unconsolidated earth materials. The bedrock geology at the site consists of serpentinite, Tertiary marine sandstone, siltstone, shale, and the Livermore Gravel Formation ` (Dibblee, 1980). The beds of the Livermore Gravel Formation situated in the eastern portion of the site strike northwesterly and dip gently to moderately to the east. The bedrock across the - _ remainder of the site generally strikes to the northwest, but the dip of the bedrock can vary from near vertical to steep or moderately steep toward the southwest (BGC, 1990). The site soil and earth materials mapped across the property by BGC (1990) include artificial fill - exposed west of the City of Pleasanton water tank on the east side of the property. Residual soil formed by the in-place weathering of the underlying bedrock was encountered on the higher -- undisturbed terrain and was up to about three feet in thickness. Colluvial soils mapped in the valleys and on-site swales were developed from the downslope creep and/or erosion of the _ residual soil. In the northern portion of the site, BGC (1990) mapped two fan deposits consisting of slope wash and debris flow materials derived from the erosion of upslope soil and weathered bedrock. Sedimentary alluvial deposits were found in the Gold Creek and Laurel Creek stream valleys and near Dublin Canyon Road in the northwest corner of the site. A number of landslide deposits were mapped across the Laurel Creek Estates property by Nilsen -- (1975). BGC (1990) mapped a total of 120 landslides through aerial photograph interpretation, site reconnaissance and test pit excavations. BGC (1990) identified seventy-three landslides within the area of proposed development (Exhibit A). 4291-W2 July 17, 1997 Revised October 9, 1997 Revised October 22, 1997 ~ 1