For a good review of the Colorado & Wyoming trackage between Jansen and the mines, I recommend Bill McKenzie's "From Mountain to Mill". Yes, it is indeed a heavy duty railroad which carried heavy coal trains for many years.
The Colorado & Wyoming is (was) a subsidiary of the Colorado Fuel & Iron (CF&I)company, which historically have been a major supplier of railroad rails. The RR had 110 miles of track around the mill proper, plus the line out of Trinidad, and another segment near Guernsey, WY to serve their iron mines.