The Russian River is located in Cascadian California. It's watershed forms the southernmost portion of Cascadia. * Much like Sonoma County, the Russian River is not always considered Cascadian California (see definition of "Cascadia" at Cascadian Review cascadiareview.org) * As such, the Russian River may also be classified as "Pacific North Coast" instead of "Cascadian California." * Other sources, such as SiteLine.org, include both the Russian River and Sonoma County as "Cascadian California."