The BN operated the Royal Slope as part of the Portland Division, 10th sub branch line Warden to Royal City until the sale of the line to Temple Industries Washington Central RR in late 1986. It was not operated at first until 1982 after the Milwaukee abandonment and sale of properties, though there was residual operations of the line after the Milwaukee shut down. The line from Warden to Othello originally was the 21st sub of the Portland Division of the BN. The Port of Royal Slope had purchased the main line from Othello to the Junction and out to Industrial Park from the Milwaukee for $300,000 and then spent a lot more money rehabilitating the line.
Washington Central operated the line for a period of time after 1986, but eventually refused to serve the line anymore due to lack of traffic. Somewhere I have the figures but there were only about 100-200 car loads most years and if I remember correctly the last year Washington Central handled the traffic there were only 51 car loads.
The Port brought in Yakima Valley or Toppenish, Simcoe and Western to operate the line, which they did for a couple of years. I think the last year they handled 9 car loads.
In 1994 the Port sold the line to the Washington State DOT. Sunfresh bought the former US Army MRS 1 from Toppenish, Simcoe and Western in 1993. I think the last car loads shipped were in 1991.