This is true everywhere, not just in California. All forty-one states with a personal income tax have laws on the books to collect taxes from non-residents who

This is true everywhere, not just in California. All forty-one states with a personal income tax have laws on the books to collect taxes from non-residents who work in their state. If you're affiliated with a pro team (including players, coaches, trainers, etc.), you can expect to file your taxes about a dozen states (plus Canada.) If you're a musician or other entertainer (circus clown, for example) on a huge tour, you could conceivably file 41 state returns plus a few for other countries.