"California taxes all taxable income with a source in California regardless of the taxpayer's residency."
True, but wage and salary (W-2) income is sourced where the services are performed. See Wages and Salaries on page 6 of this CA tax reference:
https://www.ftb.ca.gov/forms/2021/2021-1031-publication.pdf
Therefore W2 wages and salary earned by a non-resident of CA working remotely from a WA location would be sourced to WA and thus not taxable by CA.
Also. if the taxpayer maintained his primary home in WA and went to CA for a "temporary or transitory purpose" with the intent of returning to WA, he or she would be considered a non-resident of CA. See page 5 of the reference given earlier.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
