Thanks Jimmy and Jerry. I had forgotton about the air dump gondolas which most likely would have been the car of choice by MOW crews for unloading rip rap. It is a shame that all were scrapped as I am sure they would have been useful to present day operations.
There is a Bert Ward photo from July of 1947 on page 174 of Grandt's Pictorial V III showing flat # 6217 with a load of rip rap. On page 180 of the same book flat # 6507 looks to be fitted with some side stakes and ties for use maybe in the 1970 Silverton branch flood repairs.