"Squatters rights" are the same as adverse possession rights, which is a piece of statutory law in the State of Oregon. However, someone must be "squatting" on your property for a period of 10 continuous years without you there, which obviously has not happened.
If you want to get this person to leave your property, you do not have to give them 30 days notice. In fact, you don't have to give them any notice. You may be successful in calling the police to get this person to leave if they do not oblige to your request; however, sometimes police do not want to get involve.
In such a case, go to your local small claims court and request an eviction. You will have to pay a small filing fee, and in a few weeks you will get a court hearing. At that point you will get an Order from the Court directing this person to leave, or the Court constable will make them leave.
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