California Code, Probate Code - PROB § 101

(a) Upon the death of a person who is married or in a registered domestic partnership, and is domiciled in this state, one-half of the decedent's quasi-community property belongs to the surviving spouse and the other one-half belongs to the decedent.

(b) Notwithstanding subdivision (a), spouses may agree in writing to divide their quasi-community property on the basis of a non pro rata division of the aggregate value of the quasi-community property, or on the basis of a division of each individual item or asset of quasi-community property, or partly on each basis. Nothing in this subdivision shall be construed to require this written agreement in order to permit or recognize a non pro rata division of quasi-community property.