CALIFORNIA FAMILY LAW
...Income Tax Matters
......Tax Returns/Rates
.........Filing Status
............Married Filing Jointly
3 Cards On This Topic:

Married spouses who are not legally separated may file joint tax returns; common law marriage included.

Determination of whether person's filing status usually made at end of tax year.

Since taxpayer was not married under the laws of any state and never filed any return, he was not entitled to married filing joint status.