Cal. PUC § 7538

At every farm or private grade crossing of a railroad where no automatic grade crossing protective device is in place there shall be installed, as a means of protecting the crossing, one or more stop signs of the type described in Section 21400 of the Vehicle Code or of such other design as the commission may prescribe unless, after a hearing, the commission shall find that the installation of such sign or signs at a particular crossing would create a hazard or dangerous condition that would not otherwise exist. At any grade crossing where stop signs are installed or in place, before traversing such crossing the driver of any vehicle shall stop such vehicle not less than 10 nor more than 50 feet from the nearest rail of the track and while so stopped shall listen, and look in both directions along the track, for any approaching train or other equipment using such rails. The vehicle shall remain standing while any train or other equipment using such rails is approaching the crossing and is close enough to constitute a hazard. A driver of any vehicle who fails to keep his vehicle standing while any train or equipment using such rails is approaching the crossing and which is so close as to constitute a hazard is guilty of a misdemeanor.