Snow posed one of the greatest challenges for mountain railroads, especially on the Southern Pacific line over Donner Pass, where wet, heavy storms could disrupt operations despite snowsheds, pushed plows, and mechanical bulldozers. In the worst storms, railroad crews relied on rotary plows such as Southern Pacific MW208, built in 1927 as a steam-powered plow based on the widely used Leslie Patent design developed by Orange Jull in 1883 and later manufactured in large numbers by the Leslie Brothers Machine Company and the American Locomotive Company. In this design, a large cutting disk at the front spun rapidly to chew into snow and ice, break it up, and blow it through chutes away from the tracks, sometimes with extendable wings to widen the cleared path. Beginning in the late 1950s, Southern Pacific converted its steam-powered rotaries to electric power, using permanently assigned old streamlined freight locomotives called Snails to supply power while several locomotives pushed each plow, and SP 208 was the last of these rotaries to be converted to diesel when its boilers were removed in 1970. Then numbered 7208, it was one of the rotary snowplows sent to rescue the trapped City of San Francisco passenger train in January 1953, and while working down Donner Pass from the Southern Pacific terminal at Norden, California, it was caught in a snowslide with another plow and the steam locomotive pushing them; during efforts to rerail it in blizzard conditions, the machine overturned and killed engineer Raymond Holland, the only death in the incident. After its rebuilding, SP 208 also became the last rotary to work on the Western Pacific Railroad when Southern Pacific leased it there in 1974.