Cogswell Dam

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Cogswell Dam
Satellite view
Cogswell Dam is located in California
Cogswell Dam
Location of Cogswell Dam in California
CountryUnited States
LocationSan Gabriel Mountains,
Angeles National Forest,
Los Angeles County,
Coordinates34°14′41″N 117°57′55″W / 34.24472°N 117.96528°W / 34.24472; -117.96528Coordinates: 34°14′41″N 117°57′55″W / 34.24472°N 117.96528°W / 34.24472; -117.96528
Opening date1935
Owner(s)Los Angeles County Department of Public Works
Dam and spillways
Type of damRock-filled
ImpoundsWest Fork San Gabriel River
Height266 ft (81 m)
Height (foundation)280 ft (85 m)[1]
Length585 ft (178 m)
Spillway capacity59,900 cu ft/s (1,700 m3/s)[1]
CreatesCogswell Reservoir
Total capacity12,234 acre⋅ft (15,090,000 m3)
Catchment area38.4 sq mi (99 km2)
Surface area146 acres (59 ha)

Cogswell Dam is a rockfill dam on the West Fork of the San Gabriel River in Los Angeles County, California. It is in the San Gabriel Mountains, northeast of Mount Wilson, and within the Angeles National Forest.

It forms Cogswell Reservoir, which has a capacity of 8,969 acre feet (11,063,000 m3).[2]

It serves mainly for flood control in conjunction with San Gabriel Dam and Morris Dam downstream. San Gabriel Dam lies 13 miles (21 km) downstream.[3]


Bonds for the dam's construction were issued in 1924. Construction began March 1932 and was completed April 1934, at a total cost of US$3,127,762.[3]

The rock-fill dam, built by the Los Angeles County Flood Control District, is 585 feet (178 m) long, 266 feet (81 m) tall (measured from the stream bed), 18 feet (5.5 m) wide at the top, and contains 1,044,945 cubic yards (798,918 m3) of material. Its crest is 2,412 feet (735 m) above sea level and 27 feet (8.2 m) above the certified water storage elevation.[2]

The dam rests on crystalline granite bedrock. The buttress is 750 feet (230 m) thick at the base, and the height from foundation to crest is 285 feet (87 m). There are concrete cutoff walls and a concrete facing slab on the dam's upstream side.[3]

See also[edit]


  1. ^ a b [1][dead link]
  2. ^ a b "Dams Within the Jurisdiction of the State of California (A-G)" (PDF). California Department of Water Resources. Retrieved September 30, 2012.
  3. ^ a b c "Cogswell Dam" (PDF). Retrieved November 18, 2012.[permanent dead link]