Cal. PROB § 3110

(a) A proceeding under this chapter shall be brought by a petition filed in the superior court. (b) The proper county for commencement of the proceeding is the county in which a conservatorship proceeding of one of the spouses is pending. If a conservatorship proceeding is not pending, then in either of the following: (1) The county in which one or both of the spouses resides. (2) Any other county as may be in the best interests of the spouses.