Oregon constitution
Article XI: corporations and internal improvements
Section 2a

(2) In all counties having a city therein containing over 300,000 inhabitants, the county and city government thereof may be consolidated in such manner as may be provided by law with one set of officers. The consolidated county and city may be incorporated under general laws providing for incorporation for municipal purposes. The provisions of this Constitution applicable to cities, and also those applicable to counties, so far as not inconsistent or prohibited to cities, shall be applicable to such consolidated government.