The Mark West Creek drainage basin covers a large portion of Sonoma County, from Mount Saint Helena and Sonoma Mountain in the east to Forestville in the west. It includes four cities (Santa Rosa, Rohnert Park, Sebastopol, and Cotati) and the incorporated town of Windsor. Adjacent watersheds include those of Green Valley Creek, Petaluma River, Sonoma Creek, the Napa River, and the Russian River.
