In general, the regular traffic was enough to keep the line (wherever it may be) clear of normal snowfall. From time to time a "plow train" of one or two engines and a flanger would precede a train (most likely a passenger train) if very heavy snow was reported. The plow train would head out an hour or three before the schedule of the passenger train, and with a little luck it wouldn't be too late at the next division point.
Only when snowstorms were very strong, and plow trains couldn't keep the line open, would the Rotary be fired up. (I have seen it posted here that both Rotaries were kept fired up all winter long - that isn't true, they were only fired up when needed, and some winters they weren't used at all.)
OY was first up, to run west on the more forgiving 1.4% grade, and to plow DOWN the 4%. The OM was stationed in Chama, but was the "last resort" if plow trains and OY couldn't keep the line open - it would typically run to Big Horn or the Lava Loop, then return to Chama.
This sort of staged approach continued until the early 1960s, when the railroad was shut down during the worst of the winter. Tom Gildersleeve was lucky enough to get shots of plow trains in March 1963. A plow train ran east on March 14; another went west on March 20, and took 36 hours to reach Chama from Alamosa. After a few hours west, the two K36s filled out their consist - a flanger, the Jordan Spreader, and two cabooses - with freight and headed to Cumbres, where they dropped the freight cars and returned to Alamosa.
So a Rotary operation was much less common than might be thought today.
West of Chama, the line was relatively easier to keep clear because of the geography and the altitude.
Hope that helps.
JAC
