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1 <br /> MOUNTAIN HOUSE.PROPOSED ALTAMONT HEIGHTS TENTATIVE.MAY <br /> 4. ENVIRONMENTAL CHECKLIST <br /> 4.6 GEOLOGY AND SOILS <br /> SETTING <br /> Site Conditions <br /> A drainage swale runs southwest to northeast across the project site. The existing topography <br /> varies from elevation 190 at the top of the small hill in the southeast corner to approximately <br /> 152 feet in the swale at the northern boundary(Siegfried Engineering, 2006). <br /> Seismicity <br /> The San Joaquin Valley is a seismically active region of California. The active and <br /> potentially active faults in the vicinity of the project site are presented below in Table 4.6-1. <br /> Table 4.6-1 <br /> Active and Potentially Active Faults in the Vicinity <br /> of the Proposed Altamont Heights Site <br /> Fault Distance to Magnitude of Maximum <br /> Length Project Sites Earthquake <br /> Fault (miles) (miles) (Moment Magnitude)' <br /> Great Valley(Segment 6) 28 2 6.7 <br /> Great Valley(Segment 7) 28 7 6.7 <br /> Greenville-Marsh Creek 35 7 6.9 <br /> Calaveras(Northern) 84 20 6.8 <br /> Great Valley(Segment 5) 17 22 <br /> 6.5 <br /> Concord-Green Valley 44 23 6.9 <br /> Hayward 50 26 7.1 <br /> Calaveras(Southern) 62 28 6.2 <br /> Vaca I7 29 6.7 <br /> Great Valley(Segment 8) 25 35 6.6 <br /> Ortigahta 41 40 6.9 <br /> West Napa 19 44 6.5 <br /> Cordelia 12 44 6.7 <br /> Rodgers Creek 37 45 7-1- <br /> San <br /> _ISan Andreas 292 46 7.9 <br /> Note: ' The moment magnitude is related to the physical size of fault rupture,the movement across the <br /> fault,and the strength of the material that is faulted. Earthquakes with moment magnitudes of <br /> 6 or greater are capable of causing widespread damage. <br /> Source: Kleinfelder, 2006. <br /> Site Soils <br /> The subsurface conditions at the project site were explored on July 20, 2006, by drilling Five <br /> borings. Borings B-1, B-3 and B-4 were drilled to a depth of 21.5 feet,and the soils <br /> encountered were very stiff to hard sandy and silty clays. Boring B-5 was drilled to a depth <br /> 4-28 <br />