The two main mountain ranges that had to be crossed (the
Rockies and the
Cascades) required major
civil engineering works and additional locomotive power. The completion of 2,300 miles (3,700 km) of railroad through some of the most varied topography in the nation in only three years was a major feat. (Original company maps denote five mountain crossings: Belts, Rockies,
Bitterroots, Saddles, and Cascades. These are slight misnomers as the Belt Mountains and Bitterroots are part of the Rockies. In fact, the route did not cross over the
Little Beltsor
Big Belts but over the Lenep-Loweth Ridge between the
Castle Mountains and the
Crazy Mountains.)
Some historians question the choice of route, since it bypassed some population centers and passed through areas with limited local traffic potential. Much of the line paralleled the
Northern Pacific Railway.
Trains magazine called the building of the extension, primarily a long-haul route, "egregious" and a "disaster."
[5] George H. Drury listed the Pacific Extension as one of several "wrong decisions" made by the Milwaukee's management which contributed to the company's eventual failure.
[6]