Just a guess, but could it have been for loading barley? The San Luis valley is a leading producer of barely - think Coors. The ag production records for Saguache County show hay, barley, oats and potatoes as the leading crops.
I would guess the leading areas for sugar beets in Colorado were Larimer and Weld Counties. There were numerous plants in those counties all served by the Great Western Railway of Colorado. I know there were plants in Loveland and Greely along with others.
Mine will be from fenugreek seeds glued onto some coal load bases. (Easier than trying to scratchbuild something as they will be the right size for the car and just will need the glue.)
Getting back to the referenced tank cars, could anyone give me some links for prototype picts of the referenced cars? On some of the cars I can only find cars lettered for eras newer than the one I need. As I have relettered and painted enough of my own cars, I should be able to letter the needed cars. As usual any assistance that can be provided would be most welcomed.
If the plant burned coal, it wouldn’t necessarily be coming from the east in a rail car. Before the Powder River Basin area became a big coal producer, coal was often brought to Duluth / Superior on lake boats, and then moved from there to the surrounding states by Upper Midwest railroads like NP, GN, etc. (Now it works the other way around; Powder River coal is brought to Duluth / Superior and shipped east on lake boats.)
Coal was also being mined in Illinois, I suppose that coal might have been sent to your plant.