We've got quite a few in my area, most of them are related to regional or state history.

Luther Burbank Home & Gardens
http://ci.santa-rosa.ca.us/default.aspx?PageId=708

Jack London State Historic Park
http://www.parks.ca.gov/default.asp?page_id=478

Fort Ross
http://www.fortrossstatepark.org/

The town of Sonoma was the location of the Bear Flag Revolt:
http://www.californiahistory.net/5_P...war_revolt.htm

There are quite a few smaller sites, many of the wineries in the area have historic buildings.