What you saw was the abandoned ex-AT&SF grade of a portion of the Joint Line between Denver and Pueblo. The actual abandonment is between Kelker on the south side of C Spgs and Palmer Lake to the north. The line was abandoned 1n 1974. I don't know why, possibly excess capacity at the time. Freight trains now run in both directions on the UP (ex-D&RGW) between Palmer Lake and Kelker. This stretch of single track no doubt creates the long line of coal trains backed up in Denver heading south. The bi-directional Joint Line was created by the USRA in 1918 (first employee tt is dated 10/1/18) to expedite RG, C&S, AT&SF rail traffic in the Dever - Pueblo corridor. Prior to that, trains ran in both directions over their own lines (C&S / SF shared SF rails) which were often a stone's throw apart.