University of Idaho has a handy, interactive map showing various types of vegetation in the U.S. If you notice which areas are colored as "Agricultural Vegetation," it's easy to appreciate why produce-handling rail terminals like Railex and Cold Express are being built where they are, as well as unit grain train loading loops, which have been popping up one after another all over the Golden Triangle of north central Montana. It would be interesting to see this kind of map from the 1960s or earlier, which would have included many more pockets of ag activity (and related packing plants and rail spurs) in places like Orange and Riverside counties in CA.
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www.gap.uidaho.edu]