"...Oregon has a 10% state capital gains tax, but Arizona does not have one at all..."
Not exactly true. AZ does not have a separate tax rate for capital gains. Instead, it taxes capital gains at ordinary income tax rates. But it definitely does tax capital gains.
So, as @Critter-3 stated, you must report your capital gain to both states. It is taxable by AZ because that is where the property is located. And it is taxable by OR because your resident state can tax all your income. You'll be able to claim a credit on your OR return for the taxes paid to AZ, so you won't be double-taxed.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
