dougreade added a note to 17 in YH LH location and building Vol. 311 in 1871-1900 Yaquina Head Lighthouse Letter books, saying “Onealta was listed as a Benton County post office in the 1885 register of Post Offices and Postmasters.
https://books.google.com/books?id=3oxRAAAAYAAJ&pg=PA606&lpg=PA606&dq=%22onealta%22+oregon&source=bl&ots=uA89EEdmsO&sig=ACfU3U1_HPEHrxZONUULrfKOcCU”