Your situation is one of dual residency. You are a domiciliary resident of CA and a statutory resident of MA. Therefore each state may tax 100% of your income.
CA law allows CA residents to claim a credit on their CA tax return when they pay a net income tax to a state or U.S. possession on income that is also taxed by California, thus avoiding double taxation.
https://www.ftb.ca.gov/forms/2020/2020-540-s-instructions.html
File CA Schedule S with your CA tax return in order to claim the credit.
https://www.ftb.ca.gov/forms/2020/2020-540-s.pdf
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
