Technically, you need to file for both states,
but "nobody" does, unless your employer withholds for CA. See http://money.cnn.com/2013/06/28/pf/taxes/business-traveler-tax-threat/ If you live in a state without an income tax
(e.g. WA, FL or TX), it’s more likely you should file in the work states. You
can't use the "it all comes out even" rationale for not filing.
If you file, you would file a non-resident CA return and a full year resident OR return. OR will tax all your income for the year. CA will tax only your income earned while physically in CA, but give you a credit, or partial credit, for the tax you pay OR on the same income*.
*CA & OR are "reverse" or "contrary" states. In most states, your resident state gives you a credit for the tax paid to the non resident state.
