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.

It forms Cogswell Reservoir, which has a capacity of 8969 acre.ft.

The dam serves mainly for flood control in conjunction with San Gabriel Dam and Morris Dam downstream. San Gabriel Dam lies 13 mi downstream.

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.

The rock-fill dam, built by the Los Angeles County Flood Control District, is 585 ft long, 266 ft tall (measured from the stream bed), 18 ft wide at the top, and contains 1044945 yd3 of material. Its crest is 2412 ft above sea level and 27 ft above the certified water storage elevation.

The dam rests on crystalline granite bedrock. The buttress is 750 ft thick at the base, and the height from foundation to crest is 285 ft. There are concrete cutoff walls and a concrete facing slab on the dam's upstream side.