The last C&S train out of Gunnison ran in January, 1911 under the direction of conductor Blaine Markle. Curly Colligan was one of the engineers. It ran over Marshall Pass since Alpine Tunnel was full of ice. Also there was a small cave in but that didn't seem to be a problem to the C&S transportation people, according to the Colorado Rail Annual where I got the information.
In her book Goin' Railroading, Margaret Coel said her grandfather, Sam Speas, ran his engine from Buena Vista to Leadville on occasion when he was engineer on that run. Speas bumped Colligan from that job in the teens and held it almost until the line was abandoned.
It would make since to run dual-gauge trains in that territory. Running a K27 on a line where plenty of standard gauge engines were available would have been a waste of motive power. It was Marshall Pass were they were needed.