UP US-69 Bridge (Northbound)

In 1871, the Chicago & South Western Railway constructed 61 miles of new railroad between Shearwood, Missouri and Allerton, Iowa, as part of a larger project to construct a line between Leavenworth, Kansas and Washington, Iowa.  In 1873, the Des Moines, Indianola & Missouri Railroad (DMI&M) constructed a 21 mile railroad line, extending from Des Moines, Iowa south to Avon, Iowa; and west to Indianola, Iowa.  Both railroads would be sold to the Iowa Northern & Missouri Southern Railroad in 1876, which was merged into the Chicago, Rock Island & Pacific Railway in 1880.  The Rock Island had acquired and constructed a network of railroads, particularly in Iowa.  This route served as a branch line to a small town near Des Moines.  During the 1880s and 1890s, the Rock Island expanded westwards, reaching Colorado and New Mexico.  Additions to the system during the early 1900s included a number of new lines in Minnesota and northern Iowa.  In 1911, the St. Paul & Kansas City Short Line Railroad, a subsidiary of the Rock Island, constructed 65 miles between Avon, Iowa and Allerton, Iowa; connecting the two lines.  This new line was built as part of a larger project to connect the northern and southern portions of the system. To reach Kansas City, the Rock Island utilized trackage rights over the Chicago, Burlington & Quincy Railroad from Cameron Junction to Kansas City.  In 1931, the Rock Island constructed a new line from near Trenton to Birmingham, located just outside of Kansas City.  From Polo to Birmingham, the route would parallel the Chicago, Milwaukee, St. Paul & Pacific Railroad tracks, and the two railroads operated as a double track route, with separate mainlines.  In 1945, a new bridge across the Missouri River was jointly constructed by the two railroads.

The Rock Island had constructed and acquired a large railroad network throughout the Midwest.  The Kansas City-Des Moines-St. Paul route would become known as the "Spine Line".  After World War II, the Rock Island struggled to survive, proposing mergers and deferring maintenance on their routes.  The Rock Island struggled to compete with a stronger and better constructed Union Pacific system.  By 1964, the Rock Island began attempts to merge with Union Pacific, and restructure railroads west of the Mississippi River.  This merger was eventually denied, and Rock Island turned its last profit in 1965.  In the mid-1970s, the railroad was in serious decline.  The railroad received loans to attempt to fix slow orders, received new equipment and turn a profit.  By 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, and by January of 1980, the entire system was ordered to be shut down and liquidated.  Many of the lines and equipment were scrapped.  Profitable sections of railroad were prepared for sale.  The Chicago & North Western Railway (C&NW) and Soo Line both had interest in the Spine Line, with the C&NW eventually purchasing the route.  During 1982 and 1983, significant money was allocated for rebuilding the deteriorated route, and trains began using the route.  In 1995, C&NW was purchased by Union Pacific Railroad (UP).  Union Pacific continues to operate this route as the Trenton Subdivision.  CPKC now operates the former Milwaukee Road portion of this segment.