I can't speak to Cal OSHA rules but where I work, in BC/Canada, yes it would legally be the owner's responsibility. Working for a large multinational it's also

I can't speak to Cal OSHA rules but where I work, in BC/Canada, yes it would legally be the owner's responsibility. Working for a large multinational it's also our policy in the US and around the world even though it may not be legally mandated in every jurisdiction. By owning our contractors' safety performance, we are trying to remove the perverse incentive that local management had to improve their own stats by contracting everything out at the expense of overall safety.