Map of California Map of Northern California Counties Alameda County Alpine County Amador County Butte County Calaveras County Colusa County Contra Costa County Del Norte County El Dorado County Glenn County Humboldt County Lake County Lassen County Marin County Mendocino County Modoc County Napa County Nevada County Placer County Plumas County Sacramento County San Francisco County San Joaquin County San Meto County Shasta County Sierra County Siskiyou County Solano County Sonoma County Sutter County Tehama County Trinity County Tuolumne County Yolo County Yuba County