California Code, Vehicle Code - VEH § 21801

(a) The driver of a vehicle intending to turn to the left or to complete a U-turn upon a highway, or to turn left into public or private property, or an alley, shall yield the right-of-way to all vehicles approaching from the opposite direction which are close enough to constitute a hazard at any time during the turning movement, and shall continue to yield the right-of-way to the approaching vehicles until the left turn or U-turn can be made with reasonable safety.

(b) A driver having yielded as prescribed in subdivision (a), and having given a signal when and as required by this code, may turn left or complete a U-turn, and the drivers of vehicles approaching the intersection or the entrance to the property or alley from the opposite direction shall yield the right-of-way to the turning vehicle.