Califronia Vehicle Code Section 21801(a)
(Left Turn at Intersection)

The driver of a vehicle intending to turn to the left at an intersection or into public or private property, or an alley, shall yield the right-of-way to all vehicles which have approached or are approaching from the opposite direction and which are so close as to constitute a hazard at any time during the turning movement and shall continue to yield the right-of-way until such time as the left turn can be made with reasonable safety.