The watershed of the Los Angeles River covers 834 square miles (2,135 square kilometers). The Santa Monica Mountains and smaller Simi Hills border it on the east side. On the west side lies the San Gabriel Mountains and Santa Susana Mountains. Seven major tributaries flow into the Los Angeles River: Burbank Western Channel, Aliso Wash, Tujunga Wash, Verdugo Wash, Arroyo Seco, Compton Creek, and Rio Hondo. 360 square miles (920 square kilometers) of the watershed are open space, while the remaining 474 square miles (1,215 square kilometers) are highly developed with all kinds of land uses.