If you move to Michigan for a temporary purpose, while maintaining your primary home (your domicile in tax terminology) in CA, then for tax purposes you would remain a resident of CA, and ALL your income would remain taxable by CA, including income earned outside CA.
Income you earn by physically working in MI is taxable by MI, even if you are a domiciliary resident of another state.
Thus, if you maintain CA residency and have income earned in MI, you would have to file a non-resident MI tax return in addition to your home state CA tax return.
In that situation, you'd be able to take a credit on your CA return for the taxes paid to MI, so you wouldn't be double-taxed.
The tax situation would be different if:
1. You permanently moved to MI, abandoning your home in CA; or
2. You maintained CA residency but lived in MI at least 183 days during the tax year.
Post back if either of those situations apply.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
