Cal. CIV § 2183

Section Twenty-one Hundred and Eighty-three. A common carrier must deliver every passenger’s luggage, whether within the prescribed weight or not, immediately upon the arrival of the passenger at his destination; and, unless the vehicle would be overcrowded or overloaded thereby, must carry it on the same vehicle by which he carries the passenger to whom it belonged, except that where luggage is transported by rail, it must be checked and carried in a regular baggage car; and whenever passengers neglect or refuse to have their luggage so checked and transported, it is carried at their risk.