San Gabriel River Basin

San Gabriel River Basin. . The San Gabriel River flows 43 miles (69 km) through Los Angeles and Orange Counties, California in the United States. Measured to its highest headwaters in the Angeles National Forest, along, the Prairie Fork in the San Gabriel Mountains, the river is 60.0 miles (96.5 km) long, draining a watershed of 713 square miles (1,850 km2). The San Gabriel River basin includes the rugged southern slopes of the San Gabriel Mountains, the urbanized San Gabriel Valley and the similarly developed coastal plain of the Los Angeles Basin. , The river derives its name from the Spanish Mission San Gabriel Arcángel founded in 1771, now in the present day city of San Gabriel. Until the mid-20th century, the river was free, flowing with natural banks and riparian zone habitat lined with forests, marshes, and grasslands for much of its length and a large estuary at its mouth Today most of the San Gabriel River is channelized. with the section below Whittier Narrows Dam lined by concrete, and impounded in places by debris and flood control dams.