You have to pay state tax to the state that you actually worked in (if that state has state income tax). It doesn't matter where you live, or vote, or get your mail, or where your employer is located. You have to pay California tax on all the income you earned for work that you did in California. You have to file a California tax return and report the income.
Even though your permanent home is in Washington, you will probably be considered a California resident for income tax purposes for 2021. Since every state has a different definition of a resident, it is possible to be considered a resident of more than one state at the same time. So being a Washington resident would not necessarily mean that you are not a California resident. You can have only one domicile, but you can have multiple residences. The California Franchise Tax Board has a publication that explains how to determine whether you are a California resident for income tax purposes, FTB Publication 1031, "Guidelines for Determining Resident Status." Note that on page 5 it says "You will be presumed to be a California resident for any taxable year in which you spend more than nine months in this state." If you are considered a full-year or part-year resident of California you will have to pay California tax on all of your income during the period of residency, even if some of the income is not from California. You should probably consult a tax professional in California to discuss your residency situation.
Whether you are a resident or a nonresident, you will probably have to pay a penalty for not having paid any California tax during the year. You should have made estimated tax payments to California.
Here's some additional background about living in one state and working in a different state when both states have income tax. This does not apply to your particular situation, since you live in a state that has no income tax, but it might be applicable to other people who read this. Any income you earn for working is always subject to tax by the state where you did the work. This is a general rule that applies in any state that has income tax. In addition, all of your income is subject to tax by the state that you live in, no matter where the income is from. If worked in one state, and lived in a different state that also had income tax, you would also have to report the income to the state that you live in. However, one of the states would give you credit for the tax that you paid to the other state. The most common arrangement is that the state you live in gives you credit for tax you paid to the state where you worked. But there are a few cases where it's the other way around. California does it the other way around with a few other states. There are also some states that have reciprocal agreements between two states. Under a reciprocal agreement you pay tax only to the state that you live in, even if you worked in the other state.
None of this applies in Washington, since there is no state income tax. There is no credit for tax paid to another state, and no reciprocal agreements. You just pay tax to the state that you worked in.
