Appendix E - Geology and Soils Geotechnical Supporting Information COMBINED

Ninyo & Moore | Hidden Canyon Residences and Preserve, Pleasanton, California | 403620002 | February 12, 2025 (VTM, 2024). The Shriner parcel is located in the northwest corner of the site, adjacent to Dublin Canyon Road, and the larger Lester parcel covers the remaining portion of the project. Most of the site is undeveloped and used for cattle grazing, and covered with annual grasses and a few scattered trees. The natural slopes are predominately southeast and northeast facing, up to 200 feet in height, and are moderately steep inclined with slope ratios of about 5H:1V to 2½H:1V (horizontal to vertical). Steeper slopes with ratios of about 2H:1V are present along Devaney Canyon. The southeast-facing slopes drain into Devaney Canyon, which is a major tributary to Dublin Creek. The proposed project includes construction of 30 single-family residential lots, paved roadways, and graded slopes (VTM, 2024). Fill slopes planned for the site are approximately 35 feet high or less. One 2H:1V cut slope planned behind Lots 13/14 is approximately 50 feet high (Cornerstone, 2022). Cut/fill transitions are anticipated for some of the proposed building pads. Hillside grading techniques including the construction of keyways and buttresses are proposed as part of the earthwork construction. SUBSURFACE EXPLORATION A preliminary field exploration was performed in 1997 by Lowney Associates on the Lester parcel and in 2014 by Cornerstone Earth Group on the Shriner parcel. The Lowney exploration included 19 test pits excavated to depths ranging from 3 to 18 feet. Thirteen of the 19 test pits were conducted on the Lester parcel. The Lowney exploration also included seismic refraction surveys to assess the rippability of the underlying bedrock. The locations of the test pits and seismic refraction surveys, the test pit logs, results of the seismic refraction surveys, and limited laboratory test results from the Lowney study are included in the Cornerstone Earth Group (2020) report. The 2014 Cornerstone Earth Group study on the Shriner parcel included 8 test pits excavated to depths ranging from approximately 5 to 15 feet. Two supplemental borings were performed on the western end of the Shriner parcel to depths ranging from approximately 25 to 31 feet. Geologic mapping of the site was conducted by Cornerstone Earth Group in 2014, and presented on Figure 2 of their 2020 report. Limited laboratory testing was conducted by Lowney (1998). The Cornerstone Earth Group (2020) did not perform any laboratory testing as part of their study. GEOLOGIC SUMMARY The geologic conditions at the site are described in the Cornerstone Earth Group (2020) report, which references published regional geologic maps that cover the area (Dibblee, 1980; Dibblee and Minch, 2005; Graymer et al., 1996). Based on their report and regional geologic maps, the site is 2