Oregon does not have preemption, so open carry is legal as long as the specific city does not restrict it.
Not entirely correct. Technically speaking Oregon DOES have a preemption statute. ORS 166.170.
§ 166.170¹
State preemption
(1) Except as expressly authorized by state statute, the authority to regulate in any matter whatsoever the sale, acquisition, transfer, ownership, possession, storage, transportation or use of firearms or any element relating to firearms and components thereof, including ammunition, is vested solely in the Legislative Assembly.
(2) Except as expressly authorized by state statute, no county, city or other municipal corporation or district may enact civil or criminal ordinances, including but not limited to zoning ordinances, to regulate, restrict or prohibit the sale, acquisition, transfer, ownership, possession, storage, transportation or use of firearms or any element relating to firearms and components thereof, including ammunition. Ordinances that are contrary to this subsection are void. [1995 s.s. c.1 §1]
With that said, with the amount of exceptions written into the law, it is convoluted to say the least and completely useless to say the most.
For example:
§ 166.171¹
Authority of county to regulate discharge of firearms
§ 166.172¹
Authority of city to regulate discharge of firearms
§ 166.173¹
Authority of city or county to regulate possession of loaded firearms in public places
§ 166.174¹
Authority of city, county, municipal corporation or district to regulate possession or sale of firearms
§ 166.175¹
Authority of city to regulate purchase of used firearms
§ 166.176¹
Exception to preemption for certain county ordinances
Sorry, if I knew how to link all those and make it look pretty I would.