Gem Trails of Northern California https://www.amazon.com/dp/1889786284/ref=cm_sw_r_awdo_HHGJMZE8CVFB9T8A6AV4
I have a five year old version of this book. It's worth while to own.
Another good book : http://www.amazon.com/Roadside-Geology-Northern-California/dp/087842055X