Originally Posted by Bent Bloke
I imagine it is like any intersection without traffic control: first to arrive has right-of-way.
Actually the rule for cars is NOT who arrives first. It is the person on the right, no matter when they arrive.
From Oregon Revised Statutes: (emphasis mine)
Failure to yield right of way at uncontrolled intersection
(1) A person commits the offense of failure to yield the right of way at an uncontrolled intersection if the person is operating a motor vehicle that is approaching an uncontrolled highway intersection and the person does not look out for and give right of way to any driver on the right simultaneously approaching a given point, regardless of which driver first reaches and enters the intersection.