(a) For the purpose of application of the laws of succession set forth in the Probate Code to a decedent, and for the purpose of determining the validity of a marriage under the laws of this state, an alliance entered into before 1958, which, by custom of the Indian tribe, band, or group of which the parties to the alliance, or either of them, are members, is commonly recognized in the tribe, band, or group as marriage, is deemed a valid marriage under the laws of this state.
(b) In the case of these marriages and for the purposes described in subdivision (a), a separation, which, by custom of the Indian tribe, band, or group of which the separating parties, or either of them, are members, is commonly recognized in the tribe, band, or group as a dissolution of marriage, is deemed a valid divorce under the laws of this state.