California Code, Financial Code - FIN § 7502

(a) Each real estate loan shall be secured by a deed of trust, mortgage, or other transaction or instrument constituting a lien or claim, or its equivalent, upon the real estate securing the loan, according to any lawful and recognized practice that is suited to the transaction.  Any deed of trust or other instrument or transaction constituting a lien or claim is included in the term “mortgage” in this division.

(b) A mortgage shall provide specifically for full protection to the association with respect to the loan and additional advances, including any terms and conditions that the association deems necessary and appropriate to state the agreement between the parties.