Although located just north of the heavily populated Los Angeles Basin, the Santa Clara River watershed remains one of the most natural on the South Coast. It is separated from the Los Angeles Basin by the low Santa Susana Mountains, along the north side of which the Santa Clara River runs. On the east are the San Gabriel Mountains, and on the north are the Santa Ynez Mountains, Sespe Mountains, San Cayetano Mountains, and Tehachapi Mountains. Piru, Castaic and Sespe Creeks, each over long, are the primary tributaries of the Santa Clara River. While Piru and Castaic Creeks form reservoirs for the California State Water Project (Pyramid Lake and Lake Piru on Piru Creek, and Elderberry Forebay and Castaic Lake on Castaic Creek), Sespe Creek is designated a National Wild and Scenic River, unique among Southern California streams. There are 57 archaeological sites and 12 historical landmarks in the watershed.