If you worked remotely from WA for an OR company, the sourcing of your income will be where the work is performed (in your situation this would be WA).
Therefore only include the wages for work performed while located in Oregon on your OR nonresident state income tax return. So, for example, if you made $500 a week, you go to OR to work for one day and work from home (in WA) for 4 days a week then your OR source income for the week is $100 ($500 x 1 day / 5 days). You would pay OR taxes on the $100 of OR source income only on a OR nonresident state income tax return.
You will get a state tax credit on your OR resident state income tax return for any taxes paid to CA for income that is also taxed in OR.
You will need to file as non-resident for CA (for your CA source income only - your CA wages). You will also need to file a OR resident state tax return (for all income from all sources including CA wages). You will get a state tax credit in OR for any CA state taxes that you paid on your nonresident CA state tax return.
You will want to work on your non-resident CA state tax return first. You will then take a tax credit from your non-resident CA taxes on your resident OR state tax return. (Please note that you will only get a tax credit for your CA taxes up to the amount of OR taxes that would have been paid if the income was earned in OR).
You only get a state tax credit on your OR resident state tax return for CA taxes paid. You will not get a credit in CA because you are only required to report CA source income on your CA nonresident state income tax return.
Just follow the TurboTax guide when working on your states (remembering to do your non-resident state return first) and TurboTax will do all the calculations and credits to your resident states return
Here is additional information about filing in multiple states (select "see more answer" to view the entire attachment)
https://ttlc.intuit.com/replies/3300797
