It's more likely that they're storing cars on the line to Centralia and Chehalis.

I live in the Portland area, and drive up to Fort Lewis, Wash. once a month. The TR, ex-MILW line from Chehalis parallels Interstate 5 from Chehalis to Maytown, and in the 16 years I've lived in the area I've seen piggyback flats, grain hoppers, stack wells, and just plain boxcars stored on this line every time I've passed by.

Sometimes the cars were parked on the main, or just on the sidings, or both, but they've been there every time. There is currently a string of boxcars on the siding at Grand Mound, near Exit 88 on I-5, mostly old Railboxes, that has been there for years and has accumulated graffiti on every car.