East Tunnel

You enter darkness for 408 feet as you drive through East Tunnel, with stone walls pressing close on both sides before the road opens back into daylight. This tunnel is not a natural cave carved by water or glaciers—it was blasted through Piegan Mountain during early 20th-century construction of Going-to-the-Sun Road, one of the most ambitious highway projects of its era. The tunnel's walls expose the mountain's internal geology: you can see blasting scars, color banding from brown to gray to reddish tones, and rock layers representing millions of years of tectonic history. The passage demonstrates both the mountain's massive solidity and the determination of engineers who carved a through-mountain highway across the Continental Divide.