The Sunday River stuff on the C&S is indeed of the last passenger train runs and last freight runs between Leadville and Denver. These are from 16mm originals taken by Albert Hale of new england. Sunday River also has films of several of Maine 2 ft guage lines taken by the same man and also good.
Should also note that the above films along with the excellent Colorado Railroad Museum annuals on the South Park and Clear Creek lines present a good picture of the last trips on these lines.
On my wish list would be the pre war 8mm stuff taken by Richard B. Jackson now that the transfer technology for this size of film has improved. Think that WB Video may still have this tape for sale "Excursion To The Thirties".