Oregon Constitution Art. IV § 4

(1) The Senators shall be elected for the term of four years, and Representatives for the term of two years. The term of each Senator and Representative shall commence on the second Monday in January following his election, and shall continue for the full period of four years or two years, as the case may be, unless a different commencing day for such terms shall have been appointed by law.

(2) The Senators shall continue to be divided into two classes, in accordance with the division by lot provided for under the former provisions of this Constitution, so that one-half, as nearly as possible, of the number of Senators shall be elected biennially.

(3) Any Senator or Representative whose term, under the former provisions of this section, would have expired on the first Monday in January 1961, shall continue in office until the second Monday in January 1961.