Most of California's laws regarding the transport of firearms deal with handguns and other firearms that the state deems "concealable". Rifles and shotguns do not fall into these categories. So you won't find much in the penal code about rifles and shotguns, because either the state doesn't care about them, or they just haven't gotten to them yet. The only rifles and shotguns that are subject to specific transport laws are those deemed to be Assault Weapons or .50 BMG rifles. I doubt if your father will be dealing with those.
* - While the state of California's Gun Free School Zone law does not generally apply to long guns, especially those being "transported", there is still a Federal Gun Free School Zone law that does apply to them. That law states that a locked container, a locked trunk, or a locked gun rack are adequate methods of securing long guns in school zones (within 1000 feet of any K-12 school). It is probably quite remote that one would be charged with that federal law by a state law enforcement agency, and even then, the prosecutor has to prove that the gun is somehow affecting interstate commerce. With the recent rulings in the Heller and McDonald cases, it is very likely that any challenge to the federal school zone law would succeed in striking it down forever. It has already been struck down once, but now there is the Second Amendment argument to use against it. If you father decides as I have that the federal law is of no consequence, then he may transport his rifles however he wishes. But he should know that the law exists and there is a chance he could be found in violation of it. If he has any doubts, it is best to stay away from any schools, or if that is not possible, to lock the guns in cases while transporting them.