Cal. Fin. Code § 1490

A commercial bank shall not lend in the aggregate more than 5 percent of its assets upon the security of the stock of any one corporation or upon the security of the bonds of any one obligor except bonds of the United States or for the payment of which the credit of the United States is pledged, bonds of the State of California or for the payment of which the credit of the State of California is pledged, and bonds of any county, city and county, city, metropolitan water district, school district, or irrigation district of the State of California which qualify as investments for savings banks.