Inclement months on the Sierra present many operating challenges and while modern machines and technology have streamlined certain operations in the face of winter's worst intentions, these months still prove the most trying for railroading over Donner Summit. Despite the modern advances, Union Pacific still faces the unpredictable wrath of Sierra Cement, the same formidable adversary that for many decades their predecessor in the Sierra, Southern Pacific, went to battle with. To contend with the Sierra snow pack Union Pacific's snow fighters are equipped with rebuilt flangers, spreaders, and in extreme situations the rotary snow plow to ensure their Sierra Crossing continues to be a clear path for revenue. Having cleared a path from Truckee to Emigrant Gap (running in tandem with another spreader) the 'lead' spreader set, led by rebuilt spreader SPMW 4031, returns east to its winter base in Truckee, CA, running escort to an eastbound 'shooter'.
