| Cogswell Dam | |
| Location Map: | California |
| Coordinates: | 34.2447°N -117.9653°W |
| Country: | United States |
| Location: | San Gabriel Mountains, Angeles National Forest, Los Angeles County, California |
| Owner: | Los Angeles County Department of Public Works |
| Dam Height: | 266feet |
| Dam Height Foundation: | 280feet[1] |
| Dam Length: | 585feet |
| Dam Crosses: | West Fork San Gabriel River |
| Spillway Capacity: | 59900cuft/s |
| Res Name: | Cogswell Reservoir |
| Res Capacity Total: | 12234acre feet |
| Res Catchment: | 38.4mi2 |
| Res Surface: | 146acres |
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 .[2]
The dam serves mainly for flood control in conjunction with San Gabriel Dam and Morris Dam downstream. San Gabriel Dam lies downstream.[3]
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 long, tall (measured from the stream bed), wide at the top, and contains of material. Its crest is above sea level and above the certified water storage elevation.[2]
The dam rests on crystalline granite bedrock. The buttress is thick at the base, and the height from foundation to crest is . There are concrete cutoff walls and a concrete facing slab on the dam's upstream side.[3]