High Quality Content by WIKIPEDIA articles! Piru Creek is a large stream in northern Los Angeles County and eastern Ventura County, California. It is a tributary of the Santa Clara River, the largest stream system in Southern California that is still relatively natural. It drains an area of about 497 square miles (1,290 km2) and is about 71 miles (114 km) long. The creek is the Santa Clara`s largest tributary, providing about one-half of its flow. Parts of the creek are impounded in reservoirs to provide storage for irrigation and water from the California Aqueduct.