As a result of the flood of 1914, which caused an estimated $10,000,000 in property damage, in the San Gabriel Valley, the California Legislature implemented The Los Angeles County Flood Control Act that entailed a systematic study for flood relief. Results showed an average of 60,000 acre feet of water, valuing between $500,00 to $1,000,000, being wasted from the San Gabriel Mountain watershed into the ocean that could otherwise be conserved and domestically used for nearly half a million people.[1]
To address this issue, voters in 1924 approved a $35.3 million bond measure to fund the construction of a series of water conservation and flood control structures. This ambitious plan included the development of eight major dams: Thompson Creek, Big Dalton, San Gabriel, Big Santa Anita, Eaton Canyon, Big Tujunga, Pacoima, Puddingstone, and Sierra Madre. These dams were designed to not only control flooding but also to capture and store water for municipal use, marking a significant advancement in the region’s infrastructure for sustainable water management.[1]
Dam
The concrete arch dam has a height of 69 feet (21m), and a width of 200 feet (61m). Construction was completed in 1928. It is owned by Los Angeles County Department of Public Works. At the lower face of the dam, water can be released out of a steel grille covered 4 feet (1.2m) diameter outlet onto a spillway, and then into channelized Little Santa Anita Creek.
In the 1940s, CCC—Civilian Conservation Corps workers built the concrete channel containing the creek, from the dam through adjacent Sierra Madre. They also constructed public street bridges and footbridges across the channel in the Sierra Madre Canyon neighborhood.[2]
Reservoir–debris basin
The dam's debris basin, when unfilled with sediment, and a small reservoir, can have a storage capacity of 51 acre-feet (63,000m3), and a normal surface area of 1 acre. Its surrounding perimeter watershed area is 0.77 square miles (2.0km2), with some slopes coated in gunnite.[3] The upstream drainage basin for Little Santa Anita Creek is much larger.
The dam and debris basin–reservoir are used for flood and sediment control, and for downstream fish habitat protection.[3]
Access
Access to the dam is restricted by locked gates and chain link fencing across the public Sierra Madre Canyon neighborhood side.
To the west, on Mount Wilson Trail Road in the neighborhood, there is a trailhead for the historic Mount Wilson Trail, a hiking trail that climbs up through Little Santa Anita Canyon to reach Mount Wilson.[4][5][6] Other trails, now within the Angeles National Forest, branch off it to the creek for canyoneering, and to other views and destinations. Waterfalls, including a 40-foot (12m) tall one, are in the deep canyon above the dam.[6]
Environmental Considerations
The dam’s operation is carefully managed to balance flood control with environmental stewardship. Sediment removal activities are coordinated to minimize impact on downstream riparian habitats. Additionally, water releases are occasionally managed to support fish populations and maintain natural flow patterns.
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