The Mission Era
This site focuses on the history of California under Spanish and Mexican rule. It contains 49 watercolors of the California missions by artist Edward Vischer (1808-1878). Click "Container Listing" in the left frame to see the images.
http://www.oac.cdlib.org:80/dynaweb/virtual/calher/vischer

California Mission Studies Association
This site includes information on California's missions and archaeological and preservation projects as well as an illustrated glossary of mission-related terms.
http://www.ca-missions.org

Coastal Navigation and Exploration of the Monterey Bay Area
This online article by Dr. Gary Breschini provides detailed information on Spanish exploration of the California coast after 1500.
http://www.monterey.edu/other-sites/history/coastalnav.html