The AMA has a section on State Laws:
For California, it says:
Lane Splitting Not referenced in Administrative Code or Statutes
For comparison, for Florida it says:
Lane Splitting 316.209 Operating motorcycles on roadways laned for traffic (2) The operator of a motorcycle shall not overtake and pass in the same lane occupied by the vehicle being overtaken. (3) No person shall operate a motorcycle between lanes of traffic or between adjacent lines or rows of vehicles.