Earl has it right for the most part.
At the end and after the demise of Passenger Service in 1927, C&S 70, a Baldwin 2-8-0 was the mainstay power for the Clear Creek lines. This locomotive was converted from coal to oil and was preferred for this branch because it could make the full round trip from Denver up the branch and back to Denver without refueling. There are photos of all manner of 2-8-0's on the line.
Remember that some of the 2-8-0's were lighter than the 2-6-0's. The rebuilt Cookes (4-10) were mainly assigned to Passenger Service. The Cookes that retained their original boilers were less powerful and assigned (as Chris Walker's links show) to switching service. The No 13 (shown on its side above Central City) was assigned as the regular Switch Engine to the Central City mining district during that district's heyday.
The big 2-8-0's 74-76 were pretty much assigned to the South Park district and later to the Leadville-Climax run.
Oh Yes, during the uP ownership era, anything goes, as there is a photo that exists of a DSP&P Mason Bogie on the High Bridge of the Georgetown Loop.
Rick Steele