You may have some success finding photographs in the Online Archive of California. You can search the overall site, or you can choose from the selected collections linked below. Note: After performing your initial search, it may be more useful to limit the items to what you can use online. Do this by clicking "Online items available" to the right of your result list.
Yale Photogrammar - 170,000 photographs from 1935 to 1945 created by the United State’s Farm Security Administration and Office of War Information. Search by county, date, subject, photographer. Includes 170 photos from Sonoma County, especially poultry and wine industries.