UP South Skunk River Bridge (Oskaloosa)

In 1867, the Eldora Railroad and Coal Company (ERC) began construction on a 16 mile railroad, connecting Ackley, Iowa to Eldora, Iowa, completing the line in 1868.  In September, the ERC was sold to the Iowa River Railway (IRR).  Also in 1868, the IRR completed an additional 27 miles of railroad between Eldora and Marshalltown, Iowa.  In September 1869, the IRR was sold to the Central Railroad Company of Iowa (CRCI).  Between 1870 and 1871, the CRCI completed 65 miles of new railroad, extending from Northwood, Iowa; through Mason City, Iowa, to Ackley.  Also in 1871, the CRCI completed an additional 81 miles of new railroad, extending from Marshalltown to Albia, Iowa.  In 1877, the Burlington, Cedar Rapids & Northern Railway (BCR&N) completed 5 miles of new railroad between the State Line and Northwood.   Between April 1877 and early 1878, the Minneapolis & St. Louis Railway (M&StL) completed 13 miles of railroad between Albert Lea, Minnesota and the Minnesota/Iowa State Line near Northwood.  The BCR&N, CRCI and M&StL all had a joint agreement, where the M&StL used the BCR&N tracks to from the State Line to Northwood to interchange with the CRCI, in exchange for the BCR&N being permitted to use the CRCI and M&StL tracks between Albert Lea and Manly, Iowa.  In May 1879, the CRCI was sold to the Central Iowa Railway Company (CIRC).  CIRC was sold to the Iowa Railway Company in 1888, which was sold to the Iowa Central Railway (IAC) in later that year.  In early 1895, the M&StL was reorganized as the Minneapolis & St. Louis Railroad (M&StL).  In 1902, the ICR would be leased by the M&StL, and the IAC was formally sold to the M&StL in 1912.  The BCR&N agreement was maintained after the BCR&N was purchased by the Chicago, Rock Island & Pacific Railway (Rock Island) in 1903.  This section of line became part of the Rock Island "Spine Line", a major line connecting St. Paul, Minnesota and Kansas City, Missouri.

The M&StL was a small midwestern railroad, connecting Minneapolis, Minnesota to Peoria, Illinois.  The Albert Lea to Oskaloosa, Iowa segment of this line formed a portion of the principal M&StL mainline.  The M&StL mainly served as a bridge railroad, allowing eastern and western railroads to interchange while bypassing the congested terminals at Chicago.  The Oskaloosa to Albia segment of this line largely allowed for a connection with the CB&Q and connected to coalfields in south central Iowa.  Because the M&StL had light freight density and limited passenger service, the railroad survived on razor thin margins and often was in financial stress.  The M&StL would later reorganize as the Minneapolis & St. Louis Railway in approximately 1920.  Through the 1930s, the railroad focused on trimming excess routes and improving the financial situation.  After leaving receivership in 1943, the M&StL invested significant capital upgrading infrastructure and modernizing equipment.  By the 1950s, it became clear that the M&StL would need to merge with a larger railroad to survive.  In 1960, the M&StL was purchased by the Chicago & North Western Railway (C&NW) during one of the first major railroad consolidations in the second half of the 20th Century.  The same year, the M&StL would be abandoned between Givin and Eddyville in favor of the parallel Rock Island line.

The C&NW already operated an oversaturated railroad network in Iowa, although this line served as a north/south mainline for the C&NW.  C&NW maintained this route as a secondary mainline for several years.  In 1968, the C&NW purchased the Chicago Great Western Railway (CGW), which operated a parallel route between Manly and Mason City.  As a result, the C&NW abandoned the line between Manly and the north side of Mason City, and sold the remaining line in Mason City to the Iowa Traction Railroad (IATR).  In 1981, the C&NW purchased the Spine Line after the Rock Island went bankrupt.  This line was better constructed than the former M&StL, and provided a more direct route between more major terminals.  The Spine Line ran roughly parallel to this line, and at several points was within only a few miles of this line.  In 1988, the C&NW petitioned to abandon the line between Hampton and Steamboat Rock, and the line was acquired by North Central Railway Association (NCRA) and operated by the Illinois Central Railroad (IC).  The segment between Rockwell and Sheffield would be abandoned in 1990, and the segment between Maxon and Albia would be abandoned in 1994.

In 1995, the C&NW was purchased by Union Pacific Railroad (UP).  In 2001, the segment between Hampton and Geneva was abandoned, and in 2003, a connection was constructed at Chapin so that the Sheffield to Hampton segment could be abandoned, except for a short industrial lead at Chapin.  In 2006, the Iowa River Railroad was formed to purchase a segment between Steamboat Rock and Marshalltown, as well as the former NCRA line between Ackley and Steamboat Rock.  In 2007, the line between Eddyville and Maxon would be abandoned.  In 2012, the IARR abandoned the line between Steamboat Rock and Marshalltown.  In 2019, IATR abandoned the section in Mason City sso that it could be reused as a trail.  Today, UP operates the Marshalltown to Eddyville segment as the Oskaloosa Subdivision; the Albert Lea to Manly segment as part of the Albert Lea Subdivision, and the Mason City to Rockwell segment as the Rockwell Industrial Lead.  IARR continues to operate a short segment between Ackley and Steamboat Rock, and UP continues to operate a short segment at Chapin.  In Mason City, the line is currently being developed as the High Line Trail; while the Steamboat Rock to Marshalltown segment is currently being developed as the Iowa Rivers Edge Trail.  A short trail also uses the former right-of-way between Sheffield and Chapin.  The remainder of the line has been abandoned, and most has been converted to farm fields.