CVC 22517. No person shall open the door of a vehicle on the side available to moving traffic unless it is reasonably safe to do so and can be done without interfering with the movement of such traffic, nor shall any person leave a door open upon the side of a vehicle available to moving traffic for a period of time longer than necessary to load or unload passengers.

http://www.dmv.ca.gov/pubs/vctop/d11/vc22517.htm

That said, very very few drivers know or care about this law. Many have the attitude of this commenter, who seems to think that this cyclist deserved to die for having the gall to ride on the road:

So Sundance and many of you are assuming that she did not look before opening her car door?? That is ridiculous. We motorists DO have a right to open our car doors if the car is at a stop and her car was stopped. The bicyclist was clearly fault for riding in the streets right next to the cars. HELLO! Anyone heard of bike lane and if there is no bike lane then you take your chance of being hit.