I've been looking at some newspaper clippings from the closure of the Mansfield branch of the BN/GN back in 1985. The major shipper on that line is also the major shipper on the CW. Their solution to both was to truck to their mainline stations at Marlin or Wenatchee, but they also built a new unit train loader at Coulee City, and doubled their capacity there, to handle the grain from the Mansfield.
They have a staggering amount of storage capacity on the CW (and still quite a bit on the Mansfield) that they have learned to truck since Watco pulled the plug. Another problem was car supply.
If the grain wasn't being trucked to those stations, it was going 2 hours south to barge at Pasco. Trucking to the big loader at Ritzville was not really an option. It was already in a large truck, so just go the remaining distance to Pasco.