Appendix E - Geology and Soils Geotechnical Supporting Information COMBINED

LESTER-SHRINER PROPERTY 132-8-2 Page 10 Quadrangle by Weigers (2010) is not in agreement with that of Majmundar in that it shows a single small, “young, dormant” landslide within the north central portion of the Lester parcel and no landslides within the Shriners parcel. The large landslide shown within the Shriner parcel by Majmundar is shown as extending into the alluvial flats at and beyond Dublin Canyon Road. However, there are no topographic features that would suggest a lobate landslide toe in that area. The previous investigation by Lowney Associates (1998) shows four landslides on the south facing hillsides within the Lester parcel. These mapped landslides are characterized as earthflow/debris flows that are associated with colluvial-filled swales. Our observations and inferences made during our recent site reconnaissance suggests these features are not the result of slope movements but are the result of seasonal pervasive downhill creep of the surficial colluvial soils. These creeping areas are typically relatively small in size and are associated with colluvial filled swales as already mentioned. Figure 2 shows these features mapped during our aerial photo review and site reconnaissance. The identified creeping colluvial areas that are located nearest to the proposed building sites are generally small-scale, shallow and are not thought to involve bedrock. As for the large landslide mapped by Majmundar on the Shriners property, we performed two continuous dry coring explorations within this feature. Sample recovery was generally good (85 to 95%) and consistent in terms of down pressure during sampling. We did not encounter shear zones of clay gouge and although bedding orientations did vary, this variability is consistent with localized folding that was observed at exposures adjacent to the boring locations. Based on this information, it is likely that the topographic characteristics that led to this being mapped as a landslide on the map of Majmundar is more likely due to erosional processes. The current development calls for cuts and the placement of fills at the site. The proposed cuts are oriented in a north-south trend and, based on the somewhat limited amount of bedrock structural information is known at the site, would probably not result in bedding planes dipping out of slope; however, local variations in the bedrock structure can be expected and may be encountered during the site grading (see “Conclusions” section). The future design-level investigation should further define this potential. While the global stability of natural slopes at the site appears relatively stable, cuts proposed at the site during future grading should be observed by an engineering geologist to determine if some of the bedrock discontinuities (i.e., bedding or jointing) have potentially unstable geometries and, therefore, of issue in terms of stability of finished slopes. The State Seismic Hazard Zone map for the Dublin Quadrangle indicated localized areas on south-facing slopes at the site are located within an earthquake-induced landslide zone (CGS, 2008). Furthermore, Majmundar (1998) published a map indicating landslide susceptibility and indicates sloping portions of the site are designated within Zones 2 (marginally susceptible) and 3 (generally susceptible) with a minor portion located in Zone 4 (most susceptible). These designations are the result of interpretive mapping, the nature of the geologic formations and the inferred bedrock structure as extracted from regional scale published maps. Future design- level investigations at the site should include screening slope stability analyses performed in general accordance with state guidelines. Ii! CORNERSTONE EARTH GROUP