SFPUC 2001 Alameda Watershed Management Plan

III. ENVIRONMENTAL SETTING AND IMPACTSC. GEOLOGY AND SOILSand Holocene displacement are also within and adjacent to the Watershed. The major active andpotentially active local faults that could generate seismic activity affecting the Watershed arelisted in Table III.C-1. This table summarizes the historic seismic events on regional faults andestimates of maximum magnitude.The Calaveras Fault Zone is a major structural feature in California, associated with the largersystem of lateral faults that constitute the San Andreas Fault System (SFPUC, 1996). 1 Thenorthern segment of the Calaveras Fault Zone extends 32 miles from Calaveras Reservoir to thevicinity of Walnut Creek on the north and has a slip rate of approximately 6 millimeters per year(Peterson et. al, 1996). Within the Watershed, the Calaveras Fault extends along the western sideof the Arroyo de la Laguna Canyon to the Sunol Valley, along the eastern margin of the valley.Within this segment, Quaternary-aged landslides and occasional lack of surface expressionobscure the fault.1.5 SEISMIC HAZARDSSeismic hazards within the Watershed include the potential for ground surface rupture andsecondary hazards such as liquefaction and induced slope failures. Hazards due to ground ruptureare primarily considered a risk along traces of active and potentially active faults within theWatershed, and would be expected to be confined to areas along the Calaveras Fault Zone.Earthquake-generated landslides can occur in areas already susceptible to slope failure.Earthquakes may trigger landslides that might not otherwise occur until a later time. Liquefactionis the sudden loss of strength in loose, saturated, sandy materials during an earthquake, resultingin fluid-like behavior of those materials. Liquefaction can occur in areas where groundwater isshallow and materials consist of clean, poorly consolidated, fine sands.1.6 MINERAL RESOURCESTwo active sand and gravel quarries are located within the Watershed, in Sunol Valley: theMission Valley Rock Company and RMC Pacific Materials. A crushed stone quarry is proposedon Apperson Ridge (outside the boundaries of the SFPUC Watershed lands in unincorporatedAlameda County) and has received an 80-year permit to operate. The California Division ofMines and Geology classifies lands within the San Francisco-Monterey Bay region into MineralResource Zones (MRZs) mandated by the Surface Mining and Reclamation Act (SMARA) of1975 (see Regulatory Framework, below). The MRZ-2 classification includes areas whereadequate information indicates that significant mineral deposits are present, or where it is judgedthat a high likelihood exists for their presence. The MRZ-3 classification includes areascontaining mineral deposits, for which the significance cannot be evaluated from available data.Aggregate mineral resources have been identified within the Watershed lands in the AmadorValley and the Sunol Valley. MRZ-2 classifications are restricted to portions of Sunol Valley,and MRZ-3 areas are identified for thick alluvial deposits and sedimentary rocks (Stinson, et al.,1983).1 A fault zone consists of a major fault trace and includes secondary fractures originating from this fault.NOP 96.223E: Alameda Watershed Management Plan III.C-5 ESA / 930385January 2001