LIVE IN OREGON, BUT WON $1400 AT A CALIFORNIA CASINO WHILE ON VACATION....

See "Do I Have to File?" in this California tax reference:

https://www.ftb.ca.gov/forms/2023/2023-540nr-booklet.html

Likely yes but it depends on your gross income, age and filing status. Since you have CA source income then if your gross income or adjusted gross income exceeds the amounts listed for your age and filing status in steps 1 or 2 in this CA reference then you have a CA filing requirement. 

If you have a CA filing requirement, then in the "My Info" section scroll down to "Other state income" and answer "Yes" you made money in another state and select CA from the list.  This will generate the CA nonresident return.

For non resident filing requirements, CA, like most states does not,  go by only what you earned in CA  but by your total income. 

Your home state will give you a credit, or partial credit, for what you pay to CA. So, there will be little or no double taxation, but you have the hassle and cost of preparing a 2nd state return. 

If CA tax was withheld by the casino, and you gat a form W-2G, you may even get a refund. 

Q. If a got a form W-2G and I already paid (withheld) CA tax, do I still have to file a CA return. 

A. Yes, if you otherwise qualify. But, you could probably get away with not filing, as CA already got it's money.