2010 Fault Activity Map of California
The State of California Department of Conservation have released two Google Maps, the 2010 New State Geologic Map and the 2010 State Fault Activity Map. The department's website also has an interesting page that explores the history of geologic maps of California.
Both of the new maps use images overlaid on Google Maps. The maps include a transparency slider control so that you can compare the overlays with the Google Maps base tiles underneath.
2010 Geologic Map of California