California Motor Vehicle Code 21750
If a driver is behind a bicycle or a slower-moving vehicle, he can pass the person in front of him by overtaking. This is must be done carefully and without interfering with the safe operation of the overtaken vehicle or bicycle.
Passing of another vehicle is often done on two-lane roads, when the center dividing line is broken. A driver in this situation must be sure that no oncoming traffic is close before crossing over into the left lane and moving ahead of the vehicle or cyclist in the right lane.
Passing must always be done to the left of the vehicle being passed, and can be done on multi-lane roads as well. It is important to leave the passed vehicle a safe cushion of space and to not pass excessively fast or aggressively. If passing is done on two-lane road, where the driver must pass through the opposing traffic's lane, then it must be done quickly but never in excess of the speed limit.
There are times when the center dividing line is comprised of double yellow lines with or without road bumps. These are lines that are not to be crossed, and no passing or overtaken should be done where a vehicle passes over the solid double yellow lines.