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330 Land Company, LLC Arroyo Lago 9785.004.001 Design-Level Geotechnical Report Page | 6 April 16, 2024 Latest Revision October 31, 2025 2.4.3 Seismicity The San Francisco Bay Area contains numerous active faults. Figure 4 shows the approximate location of active and potentially active faults and significant historic earthquakes mapped within the San Francisco Bay Region. An active fault is defined by the state as one that has had surface displacement within Holocene time, about the last 11,700 years (CGS, 2018). To identify nearby active faults that are capable of generating strong seismic ground shaking at the site, we utilized the United States Geological Survey (USGS) Unified Hazard Tool and disaggregated the hazard at peak ground acceleration for a return period of 2,475 years. The nearest active fault with a significant contribution (greater than 1 percent) to the overall seismic hazard at the site is the Northern trace of the Calaveras fault, approximately 5 miles to the southwest. Other nearby faults capable of producing significant ground shaking at the site are shown in Table 2.4.3-1. TABLE 2.4.3-1: Active Faults Capable of Producing Significant Ground Shaking at the Site, Latitude: 37.6786 Longitude: -121.8563 SOURCE RRUP MOMENT MAGNITUDE MW (km) (miles) Calaveras (No) [4] 8.1 5.0 7.1 Las Positas [1] 8.7 5.4 5.6 Mount Diablo Thrust [0] 11.5 7.1 7.1 Greenville (No) [4] 14.6 9.1 7.0 Hayward (So) [4] 15.6 9.7 7.1 Notes: a. Fault System (Fault Section) [Fault Subsection assigned by UCERF3] b. RRUP = nearest fault-to-site rupture distance c. Fault-to-site distances and maximum moment magnitude based on USGS Unified Hazard Tool Edition: Dynamic Conterminous U.S. 2018 These results represent sources contributing at least 1 percent to the seismic hazard at the site for the peak ground acceleration and for the given return period. Gridded or areal sources are not presented; however, these sources did not contribute more than 1 percent to the seismic hazard for the peak ground acceleration and for the given return period. 2.5 SUBSURFACE CONDITIONS At the time of our field explorations, the site was occupied by vacant, lightly vegetated land. As previously discussed, the ground surface elevation of the site ranges from approximately Elevation 357 to 362 feet (NAVD88). The subsurface conditions in previous and current explorations generally encountered existing fill across the site up to 162½ feet bgs in the northern pit and up to 70 feet bgs in Busch Pit. Subsurface conditions encountered underlying the existing fill were generally interpreted as floodplain deposits. Further description of subsurface conditions of existing fill materials and native alluvium deposits are provided in the below sections. The Site Plan and exploration logs can be reviewed for specific subsurface conditions at each exploratory location. We include our boring exploration logs in Appendix A, and select previous exploration logs in Appendices D and E. The boring logs contain the soil type, color, consistency, and visual classification in general accordance with the Unified