Oregon Constitution Art. XI § 2a

(1) The Legislative Assembly, or the people by the Initiative, may enact a general law providing a method whereby an incorporated city or town or municipal corporation may surrender its charter and be merged into an adjoining city or town, provided a majority of the electors of each of the incorporated cities or towns or municipal corporations affected authorize the surrender or merger, as the case may be.

(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.