48 Degrees North

Northwest Montana’s Overlooked Engineering Wonder

The Flathead Tunnel, a 7.01-mile bore deep beneath Elk Mountain, is the second longest in the United States

By Justin Franz
Images from Archives & Special Collections, Mansfield Library, University of Montana

On June 21, 1968, President Lyndon B. Johnson pushed a button in the White House that triggered an explosion some 2,000 miles away, deep beneath the Salish Mountains in Northwest Montana. The incident wasn’t a military exercise gone wrong, but rather a ceremony to celebrate the physical opening of Flathead Tunnel, a 7.01-mile bore deep beneath Elk Mountain that today is the second longest in the United States. It was built as the result of an international treaty and a massive dam project. 

In the 1940s and 1950s, the federal government sought to create hydroelectricity and provide flood control within the Columbia River Basin. In 1961, the U.S. signed a treaty with Canada to build four dams in the basin, including one on the Kootenai River north of Libby. The flooding of the Kootenai Valley north of the damn — creating the 90-mile-long Lake Koocanusa — required relocating roads, railways and, in some cases, entire towns. But the most expensive part of the project was relocating 60 miles of Great Northern Railway track through the valley. The U.S. Corps of Army Engineers considered numerous routes through the region before settling on one that would split off from the old track near Stryker, 30 miles northwest of Whitefish, and head west through the wilderness before reconnecting with the old line near Libby. The new line would require a tunnel beneath Elk Mountain.

Work began in October 1966, as crews of hundreds of men would work three shifts a day, six days a week for four years constructing the tunnel. Workers used lasers to measure and ensure they were tunneling where they were supposed to, and when the two crews from either side finally met in the middle, they were within two inches of each other. Crews advanced into the earth an average of 66 feet a day, blowing up and moving thousands of tons of earth. One man was killed during construction. 

Images from Archives & Special Collections, Mansfield Library, University of Montana

After Johnson triggered the blast that moved the final eight feet of dirt, workers started lining the tunnel and building track. Because the tunnel was so long, they also had to build a massive ventilation system to clear locomotive fumes. The tunnel officially opened on Nov. 7, 1970 and cost more than $49 million to build. 

Today, upwards of 30 trains, including Amtrak’s Empire Builder, use the tunnel every day, and it remains an important link for the regional economy, one foretold by President Johnson a half-century ago when he called the project a “step forward” for Montana and the Pacific Northwest. 

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