Dad loved Washington and Oregon and the Milwaukee was there with his beloved SP&S.
This is August of 1973 and was probably a weekend between weeks that he had while working out of the Portland office.
See way before work at home and the internet, you actually had to leave your family behind and go to a different city to work when “Voluen-Told” to do so. Also that was how you proved your self & ascended in a company. Yep days gone by for sure.
Based on the RR Archive, this would have been five years into the upgrade from U28 to U30B.