Big Tujunga Dam, Arch dam in Los Angeles County, US.

Big Tujunga Dam is an arch dam spanning Big Tujunga Canyon in the San Gabriel Mountains, built from curved concrete that distributes water pressure efficiently. This structure was designed to hold back winter floods and provide water storage for surrounding communities.

Construction took place between 1930 and 1931 by the Los Angeles County Flood Control District to address growing flood problems in the region. The project was part of a broader strategy to protect communities in the San Gabriel Mountains from seasonal high water.

The name Tujunga derives from the Tongva village of Tujunga, or Tuxunga, meaning "old woman's place" in Tongva and Fernandeño. The Fernandeño village near the dam and canyon was Muxúnga, "place of shooting," from the verb muxú, "shoot him."

Public access to the reservoir is forbidden, so the lake and dam crest cannot be visited; the structure is seen from outside, within the Angeles National Forest northeast of Sunland. The reservoir is normally drawn down to a low level as protection against winter floods, and sediment dredged from behind the dam is compacted and stored at the Maple Canyon Sediment Placement Site less than 1 mile (1.6 km) west.

During the 1938 flood disaster, this dam played a crucial role by stopping massive debris flows that could have destroyed the communities below. This performance made it an overlooked lifesaver for the region's settlements.