Union Pacific has bought back, and/or subleased track they already own, over the San Pedro & Southwestern Railroad between Benson, AZ (on the Sunset Route) and Naco, AZ located on the US-Mexico border. The shortline currently operates between Benson and Curtiss (7 miles) to switch a chemical plant.
What makes this move by UP so incredible is the remaining 48 miles haven't seen train movements in over a decade and
most of the track was ripped up!
http://www.stb.dot.gov/filings/all.nsf/ba7f93537688b8e5852573210004b318/6216b4edd8c7883385257a6f007ae44f/$FILE/232919.pdf