Compared with Southern Pacific's sugar beet operations in California, wood chip transportation in GS drop bottom gons with side extensions in Washington, Oregon, Idaho and Montana involved far more cars on hundreds of more miles of track. California sugar beet trains tended to be unit trains of nothing but beet loads or empties going to or from a single processing plant. By contrast, Pacific Northwest local freights would routinely pick up one to three loaded chip cars a day at a dozen mills along a main or branch line, while dropping off an equal number of empty cars for the following day's use.
Southern Pacific, Milwaukee Road and Spokane, Portland & Seattle all had similar "boxcar red" 40-foot GS gons, while Northern Pacific's were painted black. Great Northern chip cars were brown, but tended to have sheet metal sides inside the steel truss frame. Union Pacific went to custom-built 50-foot chip cars earlier than the other railroads that adapted what was already paid-for, rather than spending on new low-revenue equipment. This was the philosophy behind the fact the virtually no NP, GN nor SP&S 40-foot chip car was repainted Burlington Northern green following the 1970 merger. UP's drop-bottom GS gondolas were known more for hauling coal in Utah than wood chips in the Northwest.
If you want a few drop bottom gondolas with side extensions, modeling a Pacific Northwest way freight with two or three empties and two or three loaded cars would be much more economical than creating a Southern Pacific sugar beet train where even 20 cars would seem puny. And don't forget to model the out-of-service wigwam burner near the sawmill chip loader. The inventions of particle board and compressed fireplace logs helped create the wood chip products that created the need for wood chip cars.
Gil in Oregon