Americano Creek, the Petaluma River, Tolay Creek, and Sonoma Creek are the principal streams draining the southern portion of the county. The Sonoma Valley is drained by Sonoma Creek, whose major tributaries are Yulupa Creek, Graham Creek, Calabazas Creek, Schell Creek, and Carriger Creek; Arroyo Seco Creek is a tributary to Schell Creek. Other creeks include Foss, Felta, and Mill.
Americano Creek, the Petaluma River, Tolay Creek, and Sonoma Creek are the principal streams draining the southern portion of the county. The Sonoma Valley is drained by Sonoma Creek, whose major tributaries are Yulupa Creek, Graham Creek, Calabazas Creek, Schell Creek, and Carriger Creek; Arroyo Seco Creek is a tributary to Schell Creek. Other creeks include Foss, Felta, and Mill.