Yacolt and Kalama (1907-1909? )
which has your postmark much later
A weak point of the book is the fact that the dates of operation information is current
only through 1961. Thus the large number of RPO routes disconintued withing the last
decade are not recorded, but are listed as "current" routes. This weakness is not
serious, however, since the valuable RPO postmark is not the one from the 1960's, but
the Woodburn & Brownsville (1914-1915) or Yacolt & Kalama (1907-08) or Eugene & Klamath
Falls (1926-27) postmark that lasted but a year or two.
https://www.pnwc-nrhs.org/Trainmast...-1971-03.pdf