by the MWD since building the Colorado River Aqueduct. At its peak in 1997 and 1998, the reservoir construction project employed an average of 1,800 people. At times, more than 1,900 people labored in building the reservoir's three dams. From start to finish, about 5,000 people were employed by the construction project. Dams Construction of the three dams was completed in 1999, requiring the excavation of of foundation material. The earth fill dam project required about of sand, clay and rock. Much of the materials needed were obtained from the project area. Core materials were obtained from the silty and clayey sandy alluvium in the floor of the reservoir and the rock fill came from the bedrock highlands of the reservoir's south rim. Design and construction of the dams took into consideration the threat of earthquakes with the San Jacinto Fault Zone, located about from the reservoir, and the San Andreas Fault, located about from the reservoir. West Dam The west dam rises to above the valley floor. It spans over a nearly flat alluvial valley floor between bedrock abutment ridges. About 65% of the dam's foundation area is founded on quartzite and phyllite bedrock. The remainder is founded on dense alluvium that fills three buried channels, which are up to deep. The foundation excavations were extended below the original ground surface to remove liquefaction soils that would have made the dam unstable in an earthquake. To minimize foundation seepage through the alluvium, thick cut-off walls of plastic concrete were constructed across the three alluvial channels and excavated at least into bedrock. To reduce seepage through the rock foundation, the entire core width was consolidation grouted and a double-line grout curtain was installed to a depth of approximately . Grouting of the west dam took about two years to complete and required of grout holes. East Dam The long East Dam, constructed by a Kiewit-led joint venture, is the longest of the three dams. It measures wide at the base and wide at the top. Before embankment of the dam could begin, more than of alluvium had to be excavated to reach a solid bedrock foundation. The embankment required of crushed rock. An on-site crushing plant crushed and processed over 14 million tons of rock in 20 months to supply the dam's materials. The cut-off wall, which consists of a thick plastic concrete mix constructed through the weathered portion of