Once a critical part of the longest electrified railroad in the world, the broken concrete foundation to your left is all that remains of the two-story, brick East Portal Substation.

Essentially a gigantic electric vault, East Portal was the largest of 22 substations constructed along the Milwaukee Road’s electrified portion of the main line from Harlowton, Montana to Tacoma, Washington. East Portal was one of four substations given gabled roofs to shed deep snow. Built in 1915, salvagers in the early 1980s tore the building down for its valuable brick.

The substation housed three transformers and three powerful generators which converted 100,000 volts of alternating current from Thompson Falls Dam into 3,000 volts of direct current. This energy provided the power to propel electric locomotives over the Bitterroot Mountains.

Substation automation beginning in the early 1950s allowed East Portal operators to remotely control three adjacent substations. The Milwaukee cut back the three-man crews at these remote controlled substations to reduce labor costs.

Because of fluctuations in the 3,000-volt system at each substation, substation operators made volt meter and ammeter recordings showing the output over each 24-hour period.Because of fluctuations in the 3,000-volt system at each substation, substation operators made volt meter and ammeter recordings showing the output over each 24-hour period.

This volt meter recording made at East Portal on May 10, 1969 shows the higher voltage made by supplying current to distant trains or regenerating electric locomotives returning power to the substation. Lower voltages occurred when heavy trains were motoring upgrade.