Goat Rock Beach is a sand beach in northwestern Sonoma County, California, United States.This landform is a sub-unit of Sonoma Coast State Beach, owned and managed by the State of California. At the northern terminus of Goat Rock Beach is the mouth of the Russian River, and the southern end of this crescent shaped expanse is the massive Goat Rock, an iconic outcrop of the Sonoma Coast, which is barely attached to the mainland by a narrow isthmus.