Sonoma, the last of the mission towns to be established, was fortified in the 1830s to protect Mexico's frontier from encroaching Russian settlements to the north. Picnic or dine on the historic Sonoma Plaza, then visit the former Mexican barracks and the 1823 Mission San Francisco Solano de Sonoma.
West of Sonoma, in Petaluma, board a steamboat for a ride on the Petaluma River. Then visit Petaluma Adobe State Historic Park, the remains of a once-vast rancho. Be sure to stop at the California Welcome Center in Rohnert Park and visit its excellent Sonoma County Wine Center.
Don't miss the 800-acre Jack London State Historic Park north of Sonoma near forested Glen Ellen. Survey the ruins of London's dream home, which burned down just before he and his wife moved in.