The most prominent river system within California is formed by the Sacramento River and San Joaquin River, which are fed mostly by snowmelt from the west slope of the Sierra Nevada, and respectively drain the north and south halves of the Central Valley. The two rivers join in the Sacramento-San Joaquin River Delta, flowing into the Pacific Ocean through San Francisco Bay. Many major tributaries feed into the Sacramento-San Joaquin system, including the Pit River, Feather River and Tuolumne River.