Cal. Rev. & Tax. Code § 18521

(a)
1. (1) Except as otherwise provided in this section, an individual shall use the same filing status that he or she used on his or her federal income tax return filed for the same taxable year.
2. (2) If the Franchise Tax Board determines that the filing status used on the taxpayer’s federal income tax return was incorrect, the Franchise Tax Board may, under Section 19033 (relating to deficiency assessments), revise the return to reflect a correct filing status.
3. (3) If either spouse or domestic partner was a nonresident for any portion of the taxable year, and the couple files a joint federal income tax return, the spouses or domestic partners shall be required to file a joint nonresident return.
(b) In the case of an individual who is not required to file a federal income tax return for the taxable year, that individual may use any filing status on the return required under this part that he or she would be eligible to use on a federal income tax return for the same taxable year if a federal income tax return was required.
(c) Notwithstanding subdivision (a), spouses and registered domestic partners, as described in Section 297 of the Family Code, who are registered as domestic partners as of the close of the taxable year, may file separate returns under this part if either spouse or registered domestic partner was either of the following during the taxable year:
1. (1) An active member of the Armed Forces or any auxiliary branch thereof.
2. (2) A nonresident for the entire taxable year who had no income from a California source.
(d) Notwithstanding subdivision (a), registered domestic partners, as described in Section 297 of the Family Code, who are registered as domestic partners as of the close of the taxable year and who are prohibited under federal law from filing a joint federal income tax return, shall either file a joint state income tax return or separate state income tax returns by applying the standards applicable to spouses who file separately pursuant to Section 6013 of the Internal Revenue Code. A separate return filed by a domestic partner of a registered domestic partnership shall be subject to the same conditions and limitations applicable to the separate return of a spouse.
(e) Except for taxpayers described in subdivision (c), for any taxable year with respect to which a joint return has been filed, a separate return shall not be made by either spouse or domestic partner after the period for either to file a separate return has expired.
(f) No joint return shall be made if the spouses or the domestic partners have different taxable years; except that if their taxable years begin on the same day and end on different days because of the death of either or both, then a joint return may be made with respect to the taxable year of each. The above exception shall not apply if the surviving spouse remarries or the surviving domestic partner enters into a new domestic partnership before the close of his or her taxable year, or if the taxable year of either spouse or domestic partner is a fractional part of a year under Section 443(a) of the Internal Revenue Code.
(g) In the case of the death of one spouse or domestic partner or both spouses or both domestic partners the joint return with respect to the decedent may be made only by the decedent’s executor or administrator; except that, in the case of the death of one spouse or domestic partner, the joint return may be made by the surviving spouse or surviving domestic partner with respect to both that spouse or domestic partner and the decedent if no return for the taxable year has been made by the decedent, no executor or administrator has been appointed, and no executor or administrator is appointed before the last day prescribed by law for filing the return of the surviving spouse or surviving domestic partner. If an executor or administrator of the decedent is appointed after the making of the joint return by the surviving spouse or surviving domestic partner, the executor or administrator may disaffirm the joint return by making, within one year after the last day prescribed by law for filing the return of the surviving spouse or surviving domestic partner, a separate return for the taxable year of the decedent with respect to which the joint return was made, in which case the return made by the survivor shall constitute his or her separate return.