Operating conditions in the mountain regions of the Pacific Extension proved difficult. Winter temperatures of in Montana made it challenging for steam locomotives to generate sufficient steam. The line snaked through mountainous areas, resulting in long steep grades and sharp curves. Electrification provided an answer, especially with abundant hydroelectric power in the mountains, and a ready source of copper in Anaconda, Montana. Between 1914 and 1916, the Milwaukee Road implemented a 3,000 volt direct current (DC) overhead system between Harlowton, Montana, and Avery, Idaho, a distance of . Pleased with the result, the Milwaukee electrified its route in Washington between Othello and Tacoma, a further , between 1917 and 1920. This section traversed the Cascades through the 2¼ mile (3.6 km) Snoqualmie Tunnel, just south of Snoqualmie Pass and over lower in elevation. The single track tunnel's east portal at Hyak included an adjacent company-owned ski area (1937−1950).