Cal. Civ. Proc. Code § 2024.060

Parties to an action may, with the consent of any party affected by it, enter into an agreement to extend the time for the completion of discovery proceedings or for the hearing of motions concerning discovery, or to reopen discovery after a new date for trial of the action has been set. This agreement may be informal, but it shall be confirmed in a writing that specifies the extended date. In no event shall this agreement require a court to grant a continuance or postponement of the trial of the action.