Cal. EDC § 21192

The notice shall state the time and place fixed for the hearing of the petition and shall be addressed to the founder or founders, if living, and to the spouse or surviving spouse of any deceased founder, and the living grantor or donor of any other grant or gift set out in the petition, and in general terms to all other persons having or claiming any interest in, or rights, powers, or duties over or concerning the property described in the petition; and shall direct that they and each of them appear and answer the petition on or before the time set for the hearing. The notice shall also state that unless they so appear and demur or answer, the petitioners will apply to the court to grant the prayer of the petition, and that each person failing to so appear and answer, shall be deemed to admit as true all the material allegations of the petition.