I don't think 346 never steamed in South Alamosa. At least Bob never mentioned it in Narrow Gauge News. There was talk, but I don't think he steamed it up until 1963. I think MLCo gave up in 1948 which gives it 15 years off.
It is interesting to notice that C19's in general were rather under utilized after the mid-1030's. Their most common assignments were the Gunnison - Montrose passenger until 1936 when it came off and use as switchers in Salida and Durango. Even with reboilering in the teens, they were not real popular. C-18's appeared to get more use on branch lines. Just about all of them spent time on the deadlines in Gunnison and Salida in the late 1930's. By the mid 1940's only the 340, 345, & 346 were left. Somewhere I heard they were not very popular with the crews because they rode rough at speed. The short main rod coupled to a slightly larger piston made them out of balance compared to the smaller C16's and the longer main rod equipped C18's.