@DoninGA 's answer is correct if you are a W-2 employee. However, due to a court decision earlier this year, the California FTB may now require sole proprietors selling services to California customers to file California returns, even if such services are performed wholly outside of California and the sole proprietor otherwise has no connection to California.
You can read the details on this ruling here: https://www.coblentzlaw.com/california-office-of-tax-appeals-gives-precedential-authority-to-bindley...
There have already been questions on this forum from users who've received dunning letters from the California FTB because of this ruling.
So if your California employer regards you as an independent contractor (instead of an employee) and issues you a 1099-MISC at year's end instead of a W-2, you may well have to file a non-resident CA return in addition to your UT return. In that situation, you'd be able to take a credit on your UT return for taxes paid to CA, so you wouldn't be double-taxed.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
