CA Fam Code Section 2581

For the purpose of division of property on dissolution of marriage or legal separation of the parties, property acquired by the parties during marriage in joint form, including property held in tenancy in common, joint tenancy, or tenancy by the entirety, or as community property, is presumed to be community property. This presumption is a presumption affecting the burden of proof and may be rebutted by either of the following:

(a)

A clear statement in the deed or other documentary evidence of title by which the property is acquired that the property is separate property and not community property.

(b)

Proof that the parties have made a written agreement that the property is separate property.