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MOUNTAIN 110USE PROPOSED ALTAMONT HEIGHTS TENTATIVE MAP 4. ENVLRONMENTAL CHECKLIST 4.6 GEOLOGY AND SOILS SETTING Site Conditions A drainage Swale runs southwest to northeast across the project site. The existing topography varies from elevation 190 at the top of the small hill in the southeast corner to approximately 152 feet in the Swale at the northern boundary(Siegfried Engineering, 2006)_ Seismicity The San Joaquin Valley is a seismically active region of California. The active and potentially active faults in the vicinity of the project site are presented below in Table 4.6-1. Table 4.6-1 Active and Potentially Active Faults in the Vicinity of the Proposed Altamout Heights Site Fault Distance to Magnitude of Maximum Length Project Sites Earthquake Fault (miles) ("Jes) (Moment Magnitude)' Great Valley(Segment 6) 28 2 6.7 Great Valley(Segment 7) 28 7 6.7 Greenville-Marsh Creek 35 7 6.9 Calaveras(Northern) 84 20 6.8 Great Valley(Segment 5) 17 22 6.5 Concord-Green Valley 44 23 6.9 Hayward 50 26 7.1 Calaveras(Southern) 62 28 6.2 Vaca 17 29 6.7 Great Valley(Segment 8) 25 35 6.6 Ortigalita 41 40 6.9 West Napa 19 44 6.5 Cordelia 12 44 6.7 Rodgers Creek 37 45 7.1 San Andreas 1 292 1 46 1 7.9 Note: ' The moment magnitude is related to the physical size of fault rupture,the movement across the fault, and the strength of the material that is faulted. Earthquakes with moment magnitudes of 6 or greater are capable of causing widespread damage. Source: Kleinfelder, 2006. Site Soils The subsurface conditions at the project site were explored on July 20, 2006,by drilling five borings. Borings B-1, B-3 and B-4 were drilled to a depth of 21.5 feet, and the soils encountered were very stiff to hard sandy and silty clays. Boring B-5 was drilled to a depth 4-28