The Chicago Rock Island & Pacific got as far west as Colorado Springs on its own rails, but it entered Denver by using trackage rights on Union Pacific's Kansas Pacific line between Limon and Denver. The Rock Island did have its own cutoff near Denver for freight interchange. This cutoff left the UP at Sandown, and headed northwest to freight yards north of downtown Denver. Some of this line is still in use, but a segment between the UP Denver-Cheyenne main line and the UP Kansas Pacific line has been abandoned. The view in the photo above is about one mile northwest of Sandown. The photo below is closer to Commerce City.
Thanks to Mike Palmer for contributing information about this route.