Cal. Probate Code § 8271

(a) On the filing of the petition, a summons shall be directed to the personal representative and to the heirs and devisees of the decedent, so far as known to the petitioner. The summons shall contain a direction that the persons summoned file with the court a written pleading in response to the petition within 30 days after service of the summons. Failure of a person timely to respond to the summons precludes the person from further participation in the revocation proceeding, but does not otherwise affect the person’s interest in the estate. (b) The summons shall be issued and served with a copy of the petition and proceedings had as in the case of a contest of the will. (c) If a person fails timely to respond to the summons: (1) The case is at issue notwithstanding the failure and the case may proceed on the petition and other documents filed by the time of the hearing, and no further pleadings by other persons are necessary. (2) The person may not participate further in the contest, but the person’s interest in the estate is not otherwise affected. (3) The person is bound by the decision in the proceeding.