California Code, Probate Code - PROB § 6451

(a) An adoption severs the relationship of parent and child between an adopted person and a natural parent of the adopted person unless both of the following requirements are satisfied:

(b) Neither a natural parent nor a relative of a natural parent, except for a wholeblood brother or sister of the adopted person or the issue of that brother or sister, inherits from or through the adopted person on the basis of a parent and child relationship between the adopted person and the natural parent that satisfies the requirements of paragraphs (1) and (2) of subdivision (a), unless the adoption is by the spouse or surviving spouse of that parent.

(c) For the purpose of this section, a prior adoptive parent and child relationship is treated as a natural parent and child relationship.