Cal. Probate Code § 5042

(a) Except as provided in subdivision (b), a joint tenancy between the decedent and the decedent’s former spouse, created before or during the marriage or registered domestic partnership, is severed as to the decedent’s interest if, at the time of the decedent’s death, the former spouse is not the decedent’s surviving spouse as defined in Section 78, as a result of the dissolution or annulment of the marriage or registered domestic partnership. A judgment of legal separation that does not terminate the status of spouses is not a dissolution for purposes of this section. (b) Subdivision (a) does not sever a joint tenancy in either of the following cases: (1) The joint tenancy is not subject to severance by the decedent at the time of the decedent’s death. (2) There is clear and convincing evidence that the decedent intended to preserve the joint tenancy in favor of the former spouse. (c) Nothing in this section affects the rights of a subsequent purchaser or encumbrancer for value in good faith who relies on an apparent severance under this section or who lacks knowledge of a severance under this section. (d) For purposes of this section, property held in “joint tenancy” includes property held as community property with right of survivorship, as described in Section 682.1 of the Civil Code.