This was taken in the spring of 1975. Alco #1606 "smokes it up" Probably switching cars. The Great Northern and Northern Pacific Boxcars were actually part of the Burlington Northern, which had merged in 1970. Cars from the BN and it's predecessors were common on the ARR. It's impossible to know for sure what these cars were loaded with. Lumber from the Pacific Northwest was a common load, and there were a number of freight forwarding (consolidators) in the Seattle area, which would gather small shipments together (into full carloads) to ship them to Alaska. Common items for the forwarders were appliances and household goods.