Chicago, Milwaukee, St. Paul and Pacific Railroad Company Historic District, Railroad Historic District in Bitterroot Mountains, Idaho.
The Chicago, Milwaukee, St. Paul and Pacific Railroad Company Historic District stretches over 14.5 miles through mountainous terrain and contains 14 tunnels and 26 bridges along the former Milwaukee Road route. The corridor displays the engineering structures of a historic railway corridor built to traverse difficult mountain passages.
Construction of the Pacific Extension began in 1906 as the railroad company expanded its network to compete with other carriers. The route operated through various phases before eventually ceasing service in the late 20th century.
The route gained importance because of abundant white pine forests in the area and the absence of competing rail lines nearby. This advantage shaped how the railroad company chose its expansion path through the mountains.
The area is now accessible as the Route of the Hiawatha Trail for cycling and hiking, allowing visitors to pass through historic tunnels and across bridges. The best time to visit is during warmer months when the mountain passage is fully accessible.
The line operated with electric power from 1914 to 1974, with substations at East Portal and Avery supplying trains through overhead catenary lines. This advanced technology was uncommon for mountain rail routes in the region during that era.
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