Yes, you can file single in California even if you file married filing jointly on your federal tax return.
If you file a joint tax return for federal purposes, you may file separately for California if either spouse was:
- An active member of the United States armed forces or any auxiliary military branch during 2018.
- A nonresident for the entire year and had no income from California sources during 2018.
The link below is to the California Franchise Tax Board and contains additional information you may find useful.
https://www.ftb.ca.gov/individuals/Filing-status-information.shtml
