(b) Left Turns. The approach for a left turn shall be made as close as practicable to the left-hand edge of the extreme left-hand lane or portion of the roadway lawfully available to traffic moving in the direction of travel of the vehicle and, when turning at an intersection, the left turn shall not be made before entering the intersection. After entering the intersection, the left turn shall be made so as to leave the intersection in a lane lawfully available to traffic moving in that direction upon the roadway being entered, except that upon a highway having three marked lanes for traffic moving in one direction that terminates at an intersecting highway accommodating traffic in both directions, the driver of a vehicle in the middle lane may turn left into any lane lawfully available to traffic moving in that direction upon the roadway being entered.
http://www.leginfo.ca.gov/cgi-bin/displaycode?section=veh&group=22001-23000&file=22100-22113
