The Southern Field Division assumes responsibility as water enters the Tehachapi Tunnels to cross the mountain range and then descend to the Tehachapi Afterbay. The California Aqueduct then splits into the West Branch and East Branch as it travels into the Southern California region. This section of the SWP serves three of California’s largest counties - Los Angeles, Riverside, and San Bernardino.
The East Branch carries water through Antelope Valley, the San Bernardino Mountains, and terminates at Lake Perris near the City of Riverside. The East Branch Extension, completed in 2018, delivers water to the eastern San Bernardino County communities.
Water from the West Branch flows mainly within the area of the Angeles National Forest. Vista del Lago Visitor Center is located along the West Branch, which terminates at Castaic Lake.
SWP water flows by gravity from Tehachapi Afterbay through Oso Siphon to Oso Pumping Plant. From there it is pumped into Quail Canal, which flows into Quail Lake. Water released from the lake travels through Lower Quail Canal and enters the Peace Valley Pipeline. The pipeline, serving as the penstock for Warne Powerplant, drops water about 725 feet through the plant’s turbines to produce electricity.
Water is discharged into Pyramid Lake then travels through the 7.2-mile Angeles Tunnel and into the turbines of Castaic Powerplant. Water leaving the plant enters Elderberry Forebay, which, along with Pyramid Lake, is used for pumped-storage operations.
From the forebay, water flows into Castaic Lake, which is the terminal reservoir of the West Branch. The West Branch and its facilities were constructed between 1967 and 1982.
Oso Pumping Plant
Located on the California Aqueduct about seven miles east of Gorman, Oso Pumping plant is the first major structure on the West Branch of the California Aqueduct. Constructed between 1967 and 1972, the plant lifts water 231 feet from Tehachapi Afterbay to Quail Canal which leads into Quail Lake.
Quail Dam & LakeQuail Lake, originally a pond created by a cataclysmic movement of the San Andreas Fault ages ago, was enlarged to move water safely across the fault. It receives off-peak flows from Oso Pumping Plant and provides storage. The lake also provides limited recreation, as well as fish and wildlife habitat in the Tejon Ranch area of the western Antelope Valley, about 45 miles northwest of Lancaster and 70 miles north of downtown Los Angeles. Construction of Quail Dam and Lake took place during 1967.
William E. Warne Powerplant
Warne Powerplant in Los Angeles County recovers about 25 percent of the energy used by Edmonston Pumping Plant to lift water over the Tehachapis. The plant uses the 725-foot drop from the Peace Valley Pipeline to generate electricity with its Pelton wheel turbines. Construction on the plant began in 1978 and was completed in 1982.
Pyramid Dam & Lake
Pyramid Dam and Lake are located in Los Angeles County, about 14 miles north of the town of Castaic. The lake provides storage for Castaic Powerplant, serves as an afterbay for Warne Powerplant, and offers recreational opportunities.
Construction on the dam and lake began in 1969. The 386-foot-tall earth and rock dam was completed in 1973 and named after a pyramid-shaped rock carved out by engineers building the Old Highway 99. Pyramid Lake spans 1,360 acres with depths of 700 feet and 21 miles of shoreline. The lake provides storage for the Los Angeles Department of Water and Power Castaic Powerplant.
The Vista del Lago Visitor Center is located off Interstate 5. The center is open seven days a week from 8 a.m. to 5 p.m. (except Thanksgiving, Christmas and New Year's Day) admission is free. The building offers a viewing deck with a panoramic view of Pyramid Lake and the surrounding mountains.
Castaic Dam, Lake & Lagoon
Located about 45 miles northwest of Los Angeles, Castaic Dam and Lake were constructed between 1965 to 1974. Castaic Lake provides storage and recreational opportunities for Southern Californians. Castaic Lagoon, located south of the lake, also provides recreation and serves as a recharge basin for downstream groundwater aquifers.
Located about 40 miles northwest of Los Angeles between Pyramid Lake and Castaic Lake, Castaic Powerplant was built under a cooperative agreement between DWR and the Los Angeles Department of Water and Power (LADWP). This pumping-generating plant owned and operated by LADWP recovers power from the lift over the Tehachapis and has pumpback capability for peaking capacity. Construction began in 1969 and was completed in 1973.
Elderberry Forebay and Dam
Eldeberry Forebay, located on the upper end of Castaic Lake, provides regulatory storage which can be used by Castaic Powerplant for pumpback during off-peak hours, permits submergence for the pump-generator when the lake is at its lowest operating levels, and reduces daily and weekly fluctuations in Castaic Lake. The forebay was constructed between 1965 and 1974 by the LADWP, which also operates the facility.
Starting at the Tehachapi Afterbay, water in the East Branch drops about 140 feet through Alamo Powerplant to generate electricity. Water then travels 55 miles to Pearblossom Pumping Plant, where it is lifted 540 feet. From there, water flows downhill through an open aqueduct, linked at its end to four underground pipelines that carry the water under the Mojave River bed and the Las Flores Valley floor into Mojave Siphon Powerplant to generate power before entering Silverwood Lake. Released from the lake, water passes through the San Bernardino Tunnel and plunges more than 1,400 feet through two penstocks into Devil Canyon Powerplant, where it generates power before being discharged into its two afterbays.
The afterbays supply water to contracting agencies and flow through the buried Santa Ana Pipeline to Lake Perris, the SWP’s southernmost terminus reservoir. Water from Devil Canyon also supplies water to the East Branch Extension.
Located on the East Branch of the California Aqueduct, Alamo Powerplant is located approximately 10 miles east of the town of Gorman on the Kern-Los Angeles County line. It was constructed between 1982 and 1985, with the first of two planned units operational by 1986.
Pearblossom Pumping Plant
Pearblossom Pumping Plant is located on the California Aqueduct, 12 miles east of Palmdale. Constructed from 1967 to 1973, the plant lifts water about 540 feet to continue by gravity to Silverwood Lake. Pearblossom discharges water 3,479 feet above sea level, and is the highest point along the entire California Aqueduct.
Silverwood Lake and Cedar Springs Dam
Silverwood Lake is nestled in the San Bernardino Mountains and has a lake elevation of 3,355 feet, which is the highest of the four SWP reservoirs in Southern California. Located about 30 miles north of the city of San Bernardino on the West Fork of Mojave River, the lake and dam were constructed (1968 to 1971) to provide storage, recreation, and assure continuity of discharges through Devil Canyon Powerplant.
From the south end of the lake, water leaves via the 20,064-foot-long San Bernardino Tunnel to the penstocks of the Devil Canyon Powerplant. After power production, some of the water is taken by users directly from the afterbays. The rest enters the East Branch Extension or the Santa Ana Pipeline for delivery to the SWP’s southernmost water contractors.
With four campgrounds, two swim beaches, several picnic areas, and a marina where visitors can either rent a boat or launch their own, Silverwood Lake SRA offers multiple recreational opportunities.
Mojave Siphon Powerplant
Mojave Siphon Powerplant, constructed between 1990 and 1996, is the newest SWP powerplant. It generates electricity from water flowing downhill after its 540-foot lift by Pearblossom Pumping Plant. The plant is near Silverwood Lake’s Cedar Springs Dam.
Devil Canyon Powerplant
Devil Canyon Powerplant, constructed between 1969 and 1974, has the highest hydraulic water pressure in the SWP system. A power recovery facility, Devil Canyon Powerplant is situated near the mouth of Devil Canyon at the southern base of the San Bernardino Mountains, about five miles north of San Bernardino. It generates electricity from water traveling through the plant from Silverwood Lake. The water is then discharged into two afterbays from which water is distributed to contracting water users. Water not delivered continues to Lake Perris through the Santa Ana Pipeline.
Devil Canyon Afterbay & Second Afterbay
Flows through Devil Canyon Powerplant discharge into the afterbay, constructed from 1969 to 1974. The afterbay provides a minimal amount of storage. Construction of the second afterbay (1992 to 1995), which is connected to the existing afterbay through a cross channel, increased the power plant’s operational flexibility and capacity.
Santa Ana Pipeline
This 28-mile-long buried pipeline conveys water through urbanized San Bernardino County and into Riverside County, passing near a ridge line by Sugar Loaf Mountain and crossing Moreno Valley to Lake Perris, the terminal facility on the East Branch. Constructed between 1969 and 1973, the Santa Ana pipeline provides turnouts along its alignment for water deliveries to contracting users.
Perris Dam and Lake Perris
Located in Riverside county, Lake Perris is the terminal storage facility on the East Branch and the southernmost SWP facility. Constructed between 1970 and 1974, the lake provides water supply for contracting users and fish and wildlife enhancement. It is also one of the most heavily used lakes for recreation in the State Park System.
Visitors to the 8,200-acre Lake Perris State Recreation Area (SRA) can enjoy an abundance of recreational activities, including hiking, bicycling, fishing, swimming, picnicking, camping, rock climbing, horseback riding, and visiting the Ya'i Heki' Regional Indian Museum.
Located near the south portal of the Carley V. Porter Tunnel in Cottonwood Canyon, the afterbay is where the California Aqueduct splits into the West and East Branches. It receives discharges from the tunnel through a gated control structure. The facility was constructed from 1970 to 1971.
Four tunnels traverse the Tehachapi Mountains, a rugged, semiarid barrier between the San Joaquin Valley and Antelope Valley. Pipe conduits between portals connect the four tunnels which end at the Tehachapi Afterbay. Tunnel 1, just downstream of the surge chamber which receives water lifted by Edmonston Pumping Plant, is 7,933 feet long and connects to Tunnel 2, which is 2,810 feet long. Tunnel 3 is 5,709 feet long and connects to Tunnel 4 known as the Carley V. Porter Tunnel.
The Porter Tunnel is 25,100 feet long and discharges water through a gated control structure into the Tehachapi Afterbay.
These tunnels were constructed from 1964 to 1971.
The East Branch Extension (EBX) delivers SWP water from Devil Canyon Powerplant Afterbay to eastern San Bernardino County communities. The project includes two reservoirs, four pump stations and 18.5 miles of pipeline. EBX provides a reliable water supply to San Bernardino, Mentone, Redlands, Cherry Valley, Beaumont, and San Gorgonio communities. Some of the water from EBX travels to groundwater spreading basins to help reduce demands on area aquifers and make local water supplies more sustainable.
EBX was designed and constructed in two phases from 1999 to 2018. The built Crafton Hill Reservoir, which provides 290 acre-feet of storage capacity. Three pump stations -- in Greenspot, Crafton Hills, and Cherry Valley -- as well as 13 miles of pipeline were also completed in this phase. In the second phase of construction, Citrus Reservoir was built to provide 400 acre-feet of storage capacity. Citrus Pump Station, the enlargement of Crafton Hills Pump Station, and 5.5 miles of the Mentone pipeline were also completed in this phase.