It depends on the type of gambling winnings and if you are required to file a federal income tax return.
For CA, all
gambling income is subject to CA state income tax except for CA Lottery
winnings. So if you are required to file a federal income tax return and your CA gambling winnings are not from the CA Lottery, then you will need to file a CA state income tax return to report these CA sourced gambling winnings.
You are a nonresident and would file in CA only if
You have both of the following:
CA you only must file if your income exceeds the chart:
https://www.ftb.ca.gov/forms/2017-California-Tax-Rates-and-Exemptions.shtml#ifr
I am a resident of NM but have casino winnings from CA. My losses exceed my winnings so I am not taxed federally or in NM on the winnings since I itemize my deductions. Do I need to file a nonresident CA return to report the gambling winnings? And if so, can I deduct my gambling losses on the CA return and how would I do that?
It depends.
If your California gambling winnings were from anything besides the following sources, the winnings would be taxable in California and you would need to file a nonresident California return.
You can deduct gambling losses up to the amount of gambling winnings, but only if you are able to itemize your deductions. If you are taking the standard deduction on your tax return because that amount is higher, you would not be able to deduct the gambling losses.