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Auburn-Folsom South Unit Project

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Central Valley Project
General Description| Plan| Development| Benefits

General Description

The American River Division consists of the Folsom, Sly Park, and Auburn-Folsom South Units. The division is about midway between the northern and southern extremes of the Central Valley in Sacramento, San Joaquin, Placer, and El Dorado Counties. Division lands stretch from Sugar Pine Dam in the north to Stockton in the south. Most lands served by the Division lie in the southern portion of the Division, between Sacramento and Stockton.

The Auburn-Folsom South Unit of the Central Valley Project was designed to provide a new and supplemental water supply for irrigation and municipal and industrial needs and to alleviate the badly depleted groundwater conditions in the Folsom South service area. The primary feature of the unit was to be the Auburn Dam, Powerplant, and Reservoir, located on the American River, near the town of Auburn, about 40 miles northeast of Sacramento.

Authorized in 1965, the Auburn-Folsom South Unit originally consisted of Auburn Dam, Reservoir, and Powerplant, County Line Dam and Reservoir, Sugar Pine Dam and Reservoir, and the Folsom South Canal. The completed portions of the project, Sugar Pine Dam and Reservoir, provide water for irrigation and municipal and industrial uses to the Foresthill Divide area. Folsom South Canal, about one-third complete, provides water for municipal and industrial use in Sacramento and San Joaquin Counties.

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Facility Descriptions

Auburn Dam and Reservoir

In conjunction with Folsom and Nimbus Dams and other facilities of the Central Valley Project, Auburn Reservoir would control the varying flows of the north and middle forks of the American River. Releases from the reservoir would operate Auburn Powerplant and supply the Folsom South Canal. The dam site is on the North Fork of the American River, adjacent to the city of Auburn, California.

Construction of Auburn Dam, Reservoir, and Powerplant was well under way when construction was halted because of concerns about the ability of the dam to withstand a major earthquake. Construction of the dam has been delayed due to environmental and safety concerns.

Construction of Auburn Dam required relocating several roads in the area and a bridge that would carry the roadway over a portion of the reservoir that would be created by the dam. Work on the bridge was completed in mid-1973, and dedication ceremonies took place on September 1, 1973. The Auburn-Foresthill Bridge is the second highest bridge built by the Reclamation, surpassed only by the bridge at Glen Canyon. Rising 720 feet above the valley floor, it is a 2,428 foot-long, steel truss bridge with an 862 foot-long center section and two 639 foot-long approach sections.

The diversion tunnel was completed in November 1972.

In May 1974, work began on the foundation. On August 1, 1975, an earthquake measuring 5.7 on the Richter Scale occurred near the Oroville Dam, about 50 miles northwest of the Auburn site. Although the large earth-fill structure was not damaged, the event raised concerns about the safety of dams like the thin arch concrete dam proposed for the Auburn site. While engineers and geologists began to look into the safety concerns, work at Auburn continued. In April 1976, the Association of Engineering Geologists, Seismic Hazards Committee, issued a report stating that a moderate earthquake like the 1975 event near Oroville would cause the proposed dam at Auburn to fail. Concerns about dam safety were further heightened in June 1976, when the Teton Dam in Idaho failed.

The earthquake requirements for the dam site led to a re-evaluation of the type of dam to be constructed. Alternatives being considered are rock-fill and curved concrete gravity-type dams. Reservoir capacity behind such a structure would be about 2,300,000 acre-feet.

Auburn Powerplant was to be built at the downstream toe of Auburn Dam and would house five units, each with a capacity of 150,000 kilowatts.

Sugar Pine Dam and Reservoir

Sugar Pine Dam, located on North Shirttail Canyon approximately 7 miles north of Foresthill, California, is an earth and rock-fill structure 205 feet high, with a crest length of 689 feet. The maximum base width from upstream toe to downstream toe is 984 feet; the total volume of material in the dam is 987,500 cubic feet. Reservoir capacity is 6,921 acre-feet with a surface area of 165 acres.

The dam was completed in 1982, and the project was transferred to the Foresthill Public Utility District for operation and maintenance in 1984. During the drought years from 1987 to 1992, Sugar Pine Dam was one of the shining stars of the Central Valley Project. During each year of the drought but one, the reservoir filled and spilled, and was able to meet and exceed all obligations to its water users.

Construction of the Sugar Pine Dam began in early 1979. Excavations for the foundation began in February, with work on the diversion tunnel starting in June. The tunnel was holed through on August 31. By the end of 1979, the tunnel and spillway excavations were complete, and concrete was being placed in the outlet works and spillway chute. Work on clearing the pipeline route for the eight mile-long Sugar Pine Pipeline began in October, with pipe laying operations beginning on December 12. The pipeline carries water from Sugar Pine Reservoir to the Foresthill Divide area.

Sugar Pine Pipeline is a steel and iron structure eight miles long. The diameter begins at 27-inches and reduces to 24-inches. The capacity of the pipeline is 13 cubic feet per second. The pipeline was completed in 1983.

County Line Dam and Reservoir

County Line Dam and Reservoir was to provide water for irrigation and municipal and industrial use in the Folsom-Malby area. Although authorized for construction, the project has been delayed indefinitely.

The dam, to be located on Deer Creek, about 10 miles south of Folsom Dam, would create a reservoir with a capacity of 40,000 acre-feet. County Line Dam would be an earth-fill structure 90 feet high and 585 feet long.

County Line Reservoir will operate in conjunction with pumping from Folsom Lake to provide water service in the Folsom-Malby area for municipal and industrial use.

Folsom South Canal

The Folsom South Canal was planned to be constructed in five reaches for a total length of 68.8 miles. Only the first two reaches have been built, a total length of 26.7 miles, and there are no current plans to construct the remaining three reaches, about 42 miles, delayed pending reauthorization.

The canal originates at Nimbus Dam, on the American River, in Sacramento County, and extends southward. As originally planned, it would terminate about 20 miles southeast of the city of Stockton. This concrete-lined canal has a capacity of 3,500 cubic feet per second for the first two reaches, a total of 26.7 miles. The canal has a bottom width of 34 feet, and the maximum water depth is 17.8 feet. The maximum capacity of Reaches No. 1 and 2, is 3,500 cfs.

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Settlement of the basin began about 1844. In 1848, discovery of gold near the present site of Coloma precipitated a great influx of gold seekers from all parts of the country. At the height of the gold rush, the American River foothill area was one of the most populous in the State. However, as the sources of gold were exhausted, many left the basin or turned to farming, lumbering, or service trades.

Early miners quickly recognized the potential of riverflows to help in dredging, panning, and sluicing for gold. Diversion dams began appearing on the river in the 1850`s. As mining activities declined, two of the dams were used to divert water for use in suburban Sacramento areas and remained in use until the completion of Folsom Dam in 1955. In December 1964, the last of those early diversion dams was breached by floodwaters.


Recognition of the need for a dam to regulate the erratic flows and develop the waters of the American River dates back to the 1880s. The U.S. Army Corps of Engineers had included such a recommendation in a survey of western watersheds made under the direction of President Grant. The recommendation was received, but no action was taken.

During the first 20 years of this century, various private power companies, municipalities, farm groups, and the State of California reviewed the Corps` old survey. The State envisioned a giant multipurpose water project and purchased a potential dam site on the Middle Fork, just east of Auburn. However, the deepening depression forced a halt to further planning.

One of the first proposals to construct a dam near the present Auburn Dam site was presented in a report dated February 1928. A 1934 Forest Service report discussed some of the power and water potentials of the North Fork of the American River. In May 1957, the State of California Department of Water Resources published the results of a Statewide water resources investigation. That report incorporated much of the material developed in previous investigations and envisioned an Auburn Reservoir with a tunnel to a proposed Auburn Ravine Reservoir which would permit water deliveries to be made to the Placer service area below Wise Powerhouse.

Prior to 1940, Reclamation conducted studies of various possibilities in the American River Basin. Most of the earlier studies related to the lower portion of the basin and were made in connection with the comprehensive plan for the Central Valley.

When Folsom Dam was authorized for construction as part of the Central Valley Project in 1949, the law directed the Secretary of the Interior to investigate possibilities for further projects in the American River Basin. Subsequent studies included those which led to construction of the Sly Park Unit of the Central Valley Project, and to the Auburn-Folsom South Unit.

Following extensive investigations, Reclamation issued a feasibility report on the Auburn Unit issued on January 29, 1960. Primarily because of an acceleration of the already rapid population growth in the Central Valley area and the increased need for water, a supplemental evaluation of the Auburn-Folsom South Unit was completed and a report issued on March 22, 1963. This reevaluation included a recommendation for a significant increase in Auburn Reservoir`s proposed capacity.


The Auburn-Folsom South Unit was created as part of the American River Division by the Auburn-Folsom South Authorization Act, Public Law 89-161, approved by the President on September 2, 1965 (79 Stat. 615).

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Water Supplies

In 1991, the total number of acres in the American River Division irrigated with project water was more than 7,000 acres, with a total crop value of more than $12,000,000. Most of water supplied by units of the American River Division is used for municipal and industrial purposes. In 1991, over 51,000 acre-feet of water was supplied to non-agricultural users. Of that, over 39,000 acre-feet was supplied by the Folsom Unit.

Sugar Pine Dam and Reservoir provide water for municipal and industrial use in the Foresthill Divide area. Recreational opportunities at Sugar Pine Reservoir include fishing, swimming, and camping. Sugar Pine Dam has consistently met or exceeded the needs of water users in the area is serves.

The partially completed Folsom South Canal supplies water for irrigation and municipal and industrial use in Sacramento and San Joaquin Counties. Water from the canal is also used by the Rancho Seco Nuclear Powerplant.

In the Auburn-Folsom South Unit, the primary agricultural uses are for irrigated pasture and forage crops. Grapes, orchard crops, rice, sugar beets, and tomatoes share the remaining irrigated acreage. When completed, the additional water from the Folsom South Canal is expected to be used to raise forage and various field crops.

Auburn Dam was to provide water for flood control, irrigation, recreation, municipal and industrial uses, water quality improvement, power generation, and fisheries enhancement.

County Line Dam and Reservoir was to supply water for municipal, industrial, and other local uses to the Folsom-Malby area.


The recreational opportunities offered by all units of the American River Division enhance the quality of life for those who live in the area.

The Folsom South Canal Recreation Trail provides a trail for horseback riding, bicycling, and hiking.

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Last updated: Aug 31, 2009