California Code, Financial Code - FIN § 5758

The executed agreement, or an executed counterpart of it and the respective certificate of each constituent association or any other corporation and of the surviving association shall be filed with the Secretary of State.  Neither the agreement nor any certificate shall be filed, however, unless the commissioner's written approval is attached.  The effective date of the merger or consolidation under this article shall be the date of the filing with the Secretary of State of the copy of the approved agreement of merger or consolidation.  A copy of the approved agreement certified by the Secretary of State shall be filed with the commissioner.

If the resulting association is a federal association, the effective date of merger shall be the date the merger is effective under regulations of the Office of Thrift Supervision.