Cal. Pen. Code § 270e
No other evidence shall be required to prove marriage or registered domestic partnership of spouses, or that a person is the lawful father or mother of a child or children, than is or shall be required to prove such facts in a civil action. In all prosecutions under either Section 270a or 270 of this code, Sections 970, 971, and 980 of the Evidence Code do not apply, and both spouses or domestic partners shall be competent to testify to any and all relevant matters, including the fact of marriage or registered domestic partnership and the parentage of a child or children. Proof of the abandonment and nonsupport of a spouse, or of the omission to furnish necessary food, clothing, shelter, or of medical attendance for a child or children is prima facie evidence that such abandonment and nonsupport or omission to furnish necessary food, clothing, shelter, or medical attendance is willful. In any prosecution under Section 270, it shall be competent for the people to prove nonaccess of husband to wife or any other fact establishing nonpaternity of a husband. In any prosecution pursuant to Section 270, the final establishment of paternity or nonpaternity in another proceeding shall be admissible as evidence of paternity or nonpaternity.
Ca. Pen. Code § 270e