This election, along with a simultaneous special election, was the first use of the popular vote for electing a United States Senator. In 1904, Oregon passed the Direct Primary Law via initiative, which created a non-binding pledge that members of the Legislative Assembly would select the winner of the popular vote as United States Senator. Jonathan Bourne won a narrow plurality of the popular vote at the general election in June 1906 and his selection was subsequently ratified by the Legislative Assembly on January 22, 1907.
Source for Popular Vote data: Oregon Secretary of State. Abstract of Votes Cast at a General Election held in the State of Oregon on the fourth of June, 1906, for State Officers, United States Senator and Representatives in Congress, Oregon Secretary of State (http://records.sos.state.or.us/ORSOSWebDrawer/Record/8410979) (accessed 15 Sep 2023)