California Code, Family Code - FAM § 9209

(a) Upon application by an Indian individual who has reached the age of 18 years and who was the subject of an adoptive placement, the court which entered the final decree of adoption shall inform that individual of the tribal affiliation, if any, of the individual's biological parents and provide any other information as may be necessary to protect any rights flowing from the individual's tribal relationship, including, but not limited to, tribal membership rights or eligibility for federal or tribal programs or services available to Indians.

(b) If the court records contain an affidavit of the biological parent or parents that their identity remain confidential, the court shall inform the individual that the Secretary of the Interior may, upon request, certify to the individual's tribe that the individual's parentage and other circumstances of birth entitle the individual to membership under the criteria established by the tribe.