Russian River (California) The Russian River ( (Rašen-River)) is a southward-flowing river that drains of Sonoma and Mendocino counties in Northern California. With an annual average discharge of approximately 1,600,000 acre feet (2.0 km3), it is the second-largest river (after the Sacramento River) flowing through the nine-county Greater San Francisco Bay Area, with a mainstem long. Course The Russian River springs from the Laughlin Range about east of Willits in Mendocino County. It flows generally southward to Redwood Valley, then past Calpella, where it is bordered by U.S. Route 101, to join the East Fork Russian River just below Lake Mendocino. From there the Russian River flows south, past Ukiah through the Ukiah Valley and Hopland through the Sanel Valley, and crosses into Sonoma County just north of Cloverdale. Closely paralleled by U.S. Route 101, it descends into the Alexander Valley, where it is joined by Big Sulphur Creek. It flows south past Cloverdale, Asti, and Geyserville. East of Healdsburg, Maacama Creek joins the Russian River. After it makes a series of sweeping bends, the Healdsburg Memorial Bridge carries Old Redwood Highway over the river just upstream of U.S. Route 101's Healdsburg crossing. It receives water from Lake Sonoma via Dry Creek. The river turns westward, where it is spanned by the Wohler Bridge, and it is joined by Mark West Creek north of Forestville, followed by Green Valley Creek to the south. The river passes Rio Nido and Guerneville. In that area, State Route 116 parallels the river, bordering it past Guernewood Park and Monte Rio. Austin Creek enters from the north before the River passes through Duncans Mills. State Route 1 crosses over the river before it flows into the Pacific Ocean between Jenner and Goat Rock Beach. The Russian River estuary is recognized for protection by the California Bays and Estuaries Policy. The mouth is about north of the San Francisco Bay's Golden Gate bridge. The lower Russian River is a popular spring, summer, and fall destination for navigation and recreation. It is very safe at that time for swimming and boating, with a gentle current. The river is dangerous in the winter, with swift current and muddy water. Geology The geographer R. S. Holway wrote of the Russian River in his 1917 paper "The Russian River: A Characteristic Stream of the California Coast Ranges". Originally, the Russian River was one of several rivers draining westward from the Mayacamas Mountains through the Mendocino Plateau to the sea, a region lifted up by tectonic forces. The Navarro River drained from the Cobb Mountain area, while the Russian River drained from the Mt. St. Helena area. Being at a lower elevation, the Russian River began cutting north into the drainage area of the Navarro River. Eroding up a fault line in Alexander Valley, the Russian River intersected the Navarro River just north of Cloverdale. This resulted in the stream capture of Big Sulphur Creek (formerly the upper Navarro River) and the north fork of the Navarro River, going north to Hopland and to Ukiah. The high valleys were eroded into rocky canyons for ten miles north of Cloverdale and for five miles east of Cloverdale. After establishing a connection to Clear Lake, the Russian River was beheaded from Clear Lake by a slide (at Cow Mountain, east of Ukiah). Now Clear Lake flows into the Sacramento River. The river incised a canyon into Fitch Mountain at an early time, before land levels were eroded to their present levels. The Russian River was prevented from flowing south into San Pablo Bay, due to a 113-foot high ridge at Cotati. Guerneville