and become less seasonal and more year-round, further straining the region's water security. Geography and transportation Along the center line of the Peninsula is the northern half of the Santa Cruz Mountains, formed by the action of plate tectonics along the San Andreas Fault. In the middle of the Peninsula along the fault is the Crystal Springs Reservoir. Just north of the Crystal Springs reservoir is San Andreas Lake, after which the geologic fault was originally named. The east side of the peninsula is a densely populated and largely urban and suburban area that includes portions of Silicon Valley. It forms a commuter area between San Francisco to the north and San Jose to the south. Roads Interstate 80 Interstate 280 Interstate 380 U.S. Route 101 State Route 1 State Route 9 State Route 35 State Route 82 State Route 84 State Route 85 State Route 92 State Route 109 State Route 114 State Route 237 The bridges in the Peninsula include the Dumbarton Bridge, the Golden Gate Bridge, the San Francisco - Oakland Bay Bridge, and the San Mateo-Hayward Bridge. A number of major thoroughfares run north-south: El Camino Real (SR 82) and US 101 on the east side along the bay, Interstate 280 down the center, Skyline Boulevard (SR 35) along the crest of the Santa Cruz Mountains, and SR 1 on the west along the Pacific, and SR 85 which forms the southern end of the Peninsula. Transit Caltrain is the primary passenger rail transit in the peninsula, serving much of the eastern urbanized areas of the peninsula between Mountain View (which also connects to VTA light rail) and San Francisco's 4th and King Street stationIn addition, the peninsula has access to Bay Area Rapid Transit (BART) northward of Millbrae, connecting San Mateo County and San Francisco to the East Bay through a route over and under Daly City, Glen Park, San Francisco's Mission district, and through part of Market Street subway. Bus service is predominantly served by SamTrans and the SFMTA's Muni buses, predominantly serving San Mateo and San Francisco counties respectively. In addition, southward of Palo Alto, the Santa Clara Valley Transportation Authority operates buses to other parts of Santa Clara County. Most of the peninsula's bus transit to the East Bay and North Bay flowing through San Francisco, as neither AC Transit nor Golden Gate Transit, the primary transit operators for the East and