California Code, Financial Code - FIN § 1493

A commercial bank holding a first lien on real property may take, or purchase and hold, or loan upon another and immediately junior lien but all such loans shall not exceed in the aggregate 90 percent of the sound market value of the property as determined by proper appraisal.  A commercial bank may loan not to exceed the face value of a deed of trust or mortgage which constitutes a first lien upon real property, but in no event shall any such loan exceed 90 percent of the sound market value of the property covered by said mortgage or deed of trust as determined by proper appraisal.