Historic Blue Wing Inn Adobe in Sonoma, CA once housed immigrants and families near the mission. Sonoma and Napa. The two valley's, divided by a high ridge of mountains, stretch north from the city of San Francisco's north bay area and form a backbone of the California wine industry. Sugarloaf Ridge hosts a wonderful state park. This view is the beginning of the Oakville Grade-Trinity Road drive, a spectacularly scenic connection between the two counties and wine regions.