Greg:
In the late 50s and early 60s, the Rocky Mountain RR Club ran a number of excursions on the C&S and the Great Western. They had trips from Denver to Boulder and return. They had trips on a branch from Broomfield through Lafayette, Erie, and up to Longmont. They had trips on the Lyons branch from Longmont to Lyons and return. Lyons had a wye, so they probably turned the engine there. There was also some trips out of Fort Collins on a branch up there. Go to the DPL site and search for C&S 638. I see a few Perry shots that might give you a clue.
I was a student at the Air Force Photography school in Denver in 1959 and could have made a few of those trips, but I was as poor as a church mouse and $65 a month Airman's pay did not go very far even in those days. But I did get to see the D&RGW's Royal Gorge with two Alco PAs near the Air Force Academy.