I believe the answer is head-on and port (left). The side lights are usually visible to vessels approaching from the front or the side. The red light usually indicates a vessel's port (left) side while the green light indicates a vessel's starboard (right) side. These lights ensure that there is safety at night as the vessels navigate.
Since the formation of the San Andreas Fault system 25-30 million years ago, the juxtaposition of the Pacific and North American plates has formed many faults in California that accommodate lateral motion between the plates.
hope this helps
