Cal. Lab. Code § 7000
As used in this section "caboose" means a caboose forming a part of a train and occupied by employees or caretakers, or both.
If conditions warrant it for the safety of the occupants of a caboose the conductor, in using a pusher engine, may place it ahead of the caboose.
This section applies only to main line movements of over five miles.
This section shall not prevent the use of an electric locomotive at the rear of any train.
This section shall not apply in any case of casualty, unavoidable accident, or act of God; nor under circumstances which are the result of a cause not known to, and which could not have been foreseen by, the railroad corporation, or its officer or agent in charge of a train. This section shall not apply to the operation of wrecking, or relief trains.
Ca. Lab. Code § 7000