The Pacific Railway Act of 1862 defined a network of branches that would begin at the Missouri River and join the main line of the Union Pacific Railroad in or near Nebraska. The UP was required to build the branch from Sioux City, but an 1864 amendment released the UP from this obligation, allowing any railroad arriving at Sioux City from the east, or any newly incorporated railroad, to construct the line and gain the associated land grants. The Sioux City and Pacific Railroad was organized for this purpose in August 1864, and soon came under common ownership with the Cedar Rapids and Missouri River Railroad, a land-grant company, leased by the Chicago and North Western Railway, that completed its road across Iowa to Council Bluffs in April 1867. To build the portion in Nebraska, the Northern Nebraska Air Line Railroad was incorporated in June 1867 and merged into the Sioux City and Pacific in September 1868. In August 1867 the Cedar Rapids and Missouri River opened a branch from Missouri Valley Junction west to California Junction, where the Sioux City and Pacific, funded by the Cedar Rapids and Missouri River, began constructing its line north through the Missouri River Valley, reaching Sioux City in February 1868. The line from California Junction west to Fremont, Nebraska was completed in early 1869, initially crossing the Missouri River via a car ferry. From 1870 until July 1884, the Sioux City and Pacific operated the Fremont, Elkhorn and Missouri Valley Railroad, which continued northwest from Fremont into northwestern Nebraska. The Blair Bridge opened in late 1883, replacing the car ferry across the Missouri River. In 1884, the Chicago and North Western acquired control of the Cedar Rapids and Missouri River and the connecting Chicago, Iowa and Nebraska Railroad, which had jointly purchased the Sioux City and Pacific in 1880. Operations remained separate until August 1901, when the C&NW leased and soon merged the company into itself. The line became more important in the 1960s, when the point where the UP and C&NW interchanged transcontinental traffic was moved from Council Bluffs to Fremont, allowing for a shorter route via Blair. After the UP acquired control of the C&NW in 1995, it implemented directional running in late 1996, taking eastbound trains over the longer but flatter Omaha Subdivision through Council Bluffs. However, high-priority "Z" intermodal trains use the Blair Subdivision in both directions.
