Appendix E - Geology and Soils Geotechnical Supporting Information COMBINED

LESTER-SHRINER PROPERTY 132-8-2 Page 9 As discussed in the “Subsurface” section above, the proposed development area is blanketed by a thin layer of cohesive soils underlain by bedrock. The creek area is likely underlain by young alluvial soils consisting of sands, gravels, silts and clays. Based on the above, our screening of the site for liquefaction indicates a low potential for liquefaction in the main development area. For the two proposed residential lots being considered near the northwest corner of the site, liquefaction potential is considered moderate to high. Additional investigation and analysis should be performed during the design-level investigation. 4.4 LATERAL SPREADING Lateral spreading is horizontal/lateral ground movement of relatively flat-lying soil deposits towards a free face such as an excavation, channel, or open body of water; typically lateral spreading is associated with liquefaction of one or more subsurface layers near the bottom of the exposed slope. As failure tends to propagate as block failures, it is difficult to analyze and estimate where the first tension crack will form. The site is bounded by a creek channel that is flanked by moderate to steep hillsides underlain by bedrock. As discussed, the creek channel likely has young alluvial sediments within the channel or at remnant terrace deposits that may be susceptible to lateral movement following strong ground shaking. Since bedrock is shallow on the adjacent hillsides, the potential for lateral spreading to impact the proposed development is considered low, with the exception of the proposed bridge crossing. Foundations in this area may need to be designed to tolerate impacts due to seismically-induced creek bank movement. 4.5 SEISMIC SETTLEMENT/UNSATURATED SAND SHAKING Loose unsaturated sandy soils can settle during strong seismic shaking. As the soils previously encountered at the site were predominantly medium stiff to stiff clays underlain by bedrock, in our opinion, the potential for significant differential seismic settlement affecting the proposed improvements is low. 4.6 LANDSLIDING Our review of published, regional scale landslide-themed maps indicates suspected small-scale landslides at the subject site; however, interpretations differ between the sources (Nilsen, 1975; Majmundar, 1996; Weigers 2010). It should be noted that subsequent to the issuance of our 2014 report, the California Geological Survey in 2016 made available an interactive mapping application (Landslide Inventory and Deep-Seated Landsliding Susceptibility) which compiles mapped landslides from several published sources. Our review of the CGS interactive map did not reveal any additional mapped landslides at the site other than what has already been mentioned through the map of Majmundar. Majmundar (1996) depicts three suspected earthflows on sloping portions of the Lester parcel site, and a fourth, relatively large earthflow at and extending into the Shriners parcel and inferred to have moved in a northerly direction. These slides are mapped based on interpretation of aerial photos only and not site-specific information. The mapped slides on the Lester Parcel are small-scale and are characterized by Majmundar as involving surficial soil or colluvium and is not believed to involve bedrock. The Landslide Identification map of the Dublin Ii! CORNERSTONE EARTH GROUP