The Rio Hondo is a tributary of the Los Angeles River in Los Angeles County, California, approximately 16.4 miles (26.4 km) long. As a named river, it begins in Irwindale and flows southwest to its confluence in South Gate, passing through several cities. Above Irwindale, its main stem is known as Santa Anita Creek, which extends to another 10 miles (16 km) northwards into the San Gabriel Mountains where the source, or headwaters, of the river are found.