The Eastern Idaho Railroad (reporting marks, EIRR) is a relatively new shortline operation beginning in late 1993 when it took over operation of two former Union Pacific branch lines in Idaho. The branches are disconnected and run roughly west/southwest from Minidoka, Idaho and north/northeast from Idaho Falls, Idaho (also the railroad’s headquarters). The history of these lines date back to the late 19th century and were later purchased by the Oregon Short Line. Today the Watco family of shortline railroads based out of Pittsburg, Kansas, owns the Eastern Idaho Railroad, whose base of operations is in Twin Falls. Given that the shortline, today sees a significant and growing amount of traffic its future appears to be quite stable under Watco.
Most of the Union Pacific's trackage northwest of Wyoming came through ownership of the Oregon Short Line Railway (later renamed the Oregon Short Line Railroad after the UP fell into receivership in the early 1890s), which it created in 1881 as a means of continuing to expand its system into the Northwest (the "Short Line" term meant to invoke the shortest and fastest railroad between Wyoming and western Oregon). Through the OSL, Union Pacific was eventually able to reach Portland through ownership of the Oregon Railway and Navigation Company in 1898. This was also how the OSL expanded its system for its parent by purchasing and taking over smaller lines.
The property the Eastern Idaho Railroad would come to operate was primarily built by two companies: the St. Anthony Railroad, which was incorporated in May, 1889 and constructed much of the EIRR's lines northeast of Pocatello before it was taken over by the OSL in 1910; in January of 1904 the Minidoka & Southwestern Railroad was incorporated to build the lines west of Minidoka eventually reaching towns such as Minidoka to Buhl. The M&SW was also taken over by the OSL in 1910 with the Short Line building the lines itself that would reach Declo, Jerome, and Oakley by 1912.
The Union Pacific continued to operate much of its secondary and branch
lines in the Pacific Northwest until deregulation in 1980 after which
point it began to slowly sell off or abandon segments it considered
either outright unprofitable or of too low value to retain. By 1993 the
Class I began looking to shed its secondary lines in eastern Idaho and
by November had sold to the newly formed Eastern Idaho Railroad one of
the single largest segments of track in the company's history,
comprising some 270 miles covering several various branches.
Overall the EIRR is quite busy between the two branches it
operates, seeing well over 35,000 annual carloads with traffic based in
agriculture, food-based products, coal, limestone, chemicals,
aggregates, and coal. Of note for those who have seen the railroad its
livery is interesting in being similar to that of the late Milwaukee
Road with orange along the flanks and black used towards the bottom and
top of the locomotives. Currently the Eastern Idaho's diesel
locomotive power is made up entirely of EMDs (most of which are Geeps)
and includes GP30s, GP35s (various), and SD45s. Please note that the
below road numbers are the originals assigned by the Eastern Idaho prior
to Watco ownership, although I do not believe they have since changed.