Okay Bret I agree, that boiler front would be too new and probably too large to be from the early mills. I don't remember where Mill B was located but I believe there was a an early mill at Hood River. I am going by memory of a typed manuscript I read some years ago. I think it was someones college writing project, but I don't have it and I do not remember where I got it.
Rayoneer's Clallam Bay operations never dieselized either, but I think they also closed in 1964. The tracks were not torn out untill the mid 70's however.
And for NG content, the OLC lines in Washington were almost certainly narrow gauge, possibly 42" as the equipment came from street railways.