Cal. Insurance Code § 591

In case of double insurance, the several insurers are liable to pay losses thereon as follows: (a) In fire insurance, each insurer shall contribute ratably, without regard to the dates of the several policies. (b) In marine insurance, the liability of the several insurers for a total loss, whether actual or constructive, where the policies are not simultaneous, is in the order of the dates of the several policies. No liability attaches to a second or other subsequent policy, except as to the excess of the loss over the amount of all previous policies on the same interest. If two or more policies bear the same date, they are deemed to be simultaneous, and each insurer on simultaneous policies shall contribute ratably. The insolvency of any of the insurers does not affect the proportionate liability of the other insurers. All insurers on the same marine interest shall contribute ratably for a partial or average loss.