Cogswell Dam

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

Cogswell Dam
Satellite view
Location of Cogswell Dam in California
Country	United States
Location	San Gabriel Mountains, Angeles National Forest, Los Angeles County, California
Coordinates	34°14′41″N 117°57′55″W
Opening date	1935; 90 years ago (1935)
Owner(s)	Los Angeles County Department of Public Works
Dam and spillways
Type of dam	Rock-filled
Impounds	West Fork San Gabriel River
Height	266 ft (81 m)
Height (foundation)	280 ft (85 m)[1]
Length	585 ft (178 m)
Spillway capacity	59,900 cu ft/s (1,700 m3/s)[1]
Reservoir
Creates	Cogswell Reservoir
Total capacity	12,234 acre⋅ft (15,090,000 m3)
Catchment area	38.4 sq mi (99 km2)
Surface area	146 acres (59 ha)

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

The dam 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]

Construction

Bonds for the dam's construction were issued in 1924. Construction began in March 1932 and was completed in 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

• List of dams and reservoirs in California
• San Gabriel Mountains topics
• San Gabriel River topics