Cal. Fam. Code § 8619.5

Whenever a final decree of adoption of an Indian child has been vacated or set aside or the adoptive parent voluntary consents to termination of parental rights to the child, a biological parent or prior Indian custodian may petition for return of custody and the court shall grant that petition unless there is a showing, in a proceeding subject to the provisions of Section 1912 of the Indian Child Welfare Act (25 U.S.C. Sec. 1901 et seq.), that the return of custody is not in the best interest of the child.