UP Bridge 109.90

In 1901, the Des Moines, Iowa Falls & Northern Railway (DMIF&N) constructed a 74-mile railroad line, extending from the existing Chicago, Rock Island & Pacific Railway (Rock Island) mainline at Des Moines, Iowa to Iowa Falls, Iowa.  In 1908, the DMIF&N was purchased by the St. Paul & Des Moines Railroad (StP&DM).  Between 1908 and 1909, the StP&DM constructed an additional 44 miles of new railroad, extending to Mason City, Iowa.   The StP&DM was acquired by the St. Paul & Kansas City Short Line Railroad (StP&KCSL) in 1911, which was a subsidiary of the Rock Island.  The purpose of the StP&KCSL was to construct a direct route between St. Paul, Minnesota and Kansas City, Missouri.  The Rock Island already owned a line across Missouri, as well as a line between Albert Lea, Minnesota and St. Paul, Minnesota.  The StP&KCSL completed the connection between the two lines in 1913.  To reach the existing line at Albert Lea, the Rock Island obtained trackage rights over the Chicago Great Western Railway (CGW) between Mason City and Manly, Iowa; and over the Minneapolis & St. Louis Railway (M&StL) between Manly and Albert Lea.  The Rock Island was a large railroad, having constructed and acquired a significant railroad network in the central United States.  This line provided a critical north-south connection between the northern and southern halves of the system.  The line became known as the "Spine Line".

The Rock Island struggled financially throughout much of its history, experiencing repeated bankruptcies and chronic instability.  In the early 1930s, the Rock Island constructed a new cutoff into Kansas City, further improving the route.  After World War II, the Rock Island struggled to survive, proposing mergers and deferring maintenance on their routes. The railroad reorganized as the Chicago, Rock Island & Pacific Railroad in 1948, and the StP&KCSL was merged into the Rock Island at this time.  Throughout the 20th Century, this line remained a critical mainline for the Rock Island.  By the mid-1970s, the railroad was in serious decline.  The railroad secured loans to eliminate slow orders, acquired new equipment, and attempted to restore profitability.  Several sections of this line had fallen into serious disrepair, hampering the Rock Islands ability to maintain efficient operations.  In 1978, the railroad came close to profit, but creditors were lobbying for a complete shutdown of the Rock Island.  During the fall of 1979, a strike crippled the railroad.  Many of the lines and equipment were scrapped.  Profitable sections of railroad were prepared for sale.  After the fall of the Rock Island, a bidding war ensued between the Chicago & North Western Railway (C&NW) and the Soo Line for the Spine Line.  Ultimately, the C&NW was awarded the rights to purchase the line in 1981.  Work on rehabilitating the line began soon after, and by 1983, the entire line had been extensively rebuilt.  In 1995, the C&NW was purchased by Union Pacific Railroad (UP).  Today, UP operates the Des Moines to Mason City segment of the Spine Line as the Mason City Subdivision.