This line was originally part of UP's branch from Brighton, on the Denver-Cheyenne main line, to Boulder.  It was built in the late 1800s. In later years UP built additional branch lines in the area north of Denver to serve the various farms and mines.  The Boulder branch was later served via another branch line connection at St. Vrains. The Brighton to St. Vrains section was abandoned, probably in the 1970s. There are still some traces of track in Brighton near the junction with the main line.  There was a water treatment plant on the west side of Brighton that continued to keep a freight connection after the rest of the segment was abandoned, but that too is now without rail service. Further west, some of the right of way is used as dirt roads; other sections are completely obliterated by cropland.