San Gabriel River (California) - Course

Course

The East, West and North Forks of the San Gabriel River, rising in the San Gabriel Mountains inside the Angeles National Forest, form the source headwaters of the river. The East Fork, sometimes considered part of the main stem, rises in the shadow of Mount San Antonio as two smaller forks of its own, the Prairie Fork and the Fish Fork. The East Fork officially begins at the confluence of the Prairie Fork and a smaller tributary, Vincent Gulch. The Fish Fork and the main stem combine at the base of Iron Mountain in a canyon nearly 5,000 feet (1,500 m) deep. From there, the East Fork flows south then turns west, flowing into the east arm of San Gabriel Reservoir. The similarly sized West Fork starts near San Gabriel Peak near the Angeles Crest Highway and flows east before being impounded in Cogswell Reservoir, where it receives Devils Canyon Creek. The river continues to flow east and receives Bear Creek from the left before combining with the North Fork, which rises near Mount Islip.

San Gabriel Reservoir and Morris Reservoir, both formed by flood prevention dams built in the 20th Century, submerge most of the upper stretches of the main stem San Gabriel. It is not long after the river leaves the San Gabriel Canyon and exits from the mountains into the San Gabriel Valley near the city of Azusa. The normally dry riverbed proceeds southwest to the Santa Fe Dam, which impounds the river in the Santa Fe Flood Control Basin. After exiting the dam, the river flows south in a flood control channel roughly parallel to Interstate 605, also called the San Gabriel River Freeway, past Covina and El Monte, receives Walnut Creek and San Jose Creek from the left in quick succession, then proceeds into the Whittier Narrows where it is impounded behind Whittier Narrows Dam. Here, the river receives the Rio Hondo from the right, then splits in two immediately after: the main stem continues to flow south, while the Rio Hondo carries a portion of the water southwest to empty into the Los Angeles River near Downey.

The San Gabriel River, however, continues to flow south, past Bellflower and Cerritos. It forms the boundary between Los Angeles and Orange Counties for a brief stretch before merging with Coyote Creek, one of its main tributaries, near Los Alamitos. The river eventually becomes tidal and empties into the outlet of Alamitos Bay between the cities of Long Beach and Seal Beach.