[1] The estimated cost to build the tunnels was US$8 million (equivalent to $38,464,800 in 2023[8]); at the time this was the most expensive single construction contract awarded by the Nevada Department of Highways, predecessor agency to the Nevada Department of Transportation.

Completion was originally scheduled for late 1974, however during boring fragmented rock was discovered which slowed progress.

In 1908, a rock slide nearly caused the Southern Pacific tunnel to collapse resulting in a massive effort to save the rail line.

[10] In 1939, the City of San Francisco passenger train derailed on one of the Humboldt river bridges, killing 24 and injuring 121.

In 2008, a train derailment at a smaller tunnel west of Carlin led to the collapse of one of the Humboldt River bridges.