Found this interesting info on California law regarding passing, etc...
CVC525 states: " 'Right-of-way' is the privilege of the immediate use of the highway."
5. When a motorist is driving on a two-lane highway (one lane in each direction) and is driving slow enough to cause five or more vehicles to back up behind his or her vehicle, that motorist must pull off the road at the nearest designated turnout (or wherever there is enough room to turn out safely) to allow the backed-up traffic to pass.
"(a) No person shall drive upon a highway at such a slow speed as to impede or block the normal and reasonable movement of traffic, unless the reduced speed is necessary for safe operation, because of grade, or in compliance with law.