The Utah Southern Railroad was built by the Mormons in 1871 to connect Salt Lake City to points south. The line was acquired by the Union Pacific Railroad in 1975. Under UP ownership the Utah Southern Railroad was initially kept as a separate division, but over time was moved around and divided among different UP subsidiaries. A significant portion of the line, from Provo to Lynndyl is today known as the Sharp Subdivision. The Union Pacific sold the northern portion of the line to the Utah Transit Authority which today uses the line for light rail.
History
The first portion of the line was constructed between Salt Lake City and York (south of Santaquin), and acquired by the Union Pacific Railroad (UP) in 1875. Under UP ownership, extensions to the line reached as far south and west as Frisco. In 1881 the railroad was merged into the Utah Central Railway, another UP subsidiary. In 1889 the line was transferred to the Oregon Short Line and Utah Northern Railway, another UP subsidiary.
During construction the Los Angeles and Salt Lake Railroad, then partially owned and later fully owned by the Union Pacific, acquired the line. The portion of the former Utah Southern from Lynndyl to Milford was used for the LA&SL main, and remains in use as the primary Southern California - Utah rail trunk today. The remainder of the former Utah Southern became spurs from the LA&SL main. The spurs to Eureka and Frisco were eventually abandoned. The line between Provo and Lynndyl is still part of the Union Pacific, but is today used as a secondary route, and is known as the Sharp Subdivision.
Between Salt Lake City and Provo the line ran roughly parallel to the Denver and Rio Grande Western's Utah Division. Between these cities, the former Utah Southern route became a secondary route after the two companies began sharing track in the 1980s. This portion was later sold to the Utah Transit Authority and provides the corridor for a significant part of the TRAX light rail system, forming almost the entirety of the corridor of the Blue Line. Freight traffic on this portion is now managed by the Salt Lake City Southern Railroad.