
As auto-touring increased, the newly-formed National Park Service recognized that roads needed improvement. Road-building in this region was not easy. Granite rock was blasted away to form roadbeds. Powderhouses were used to store blasting powder. In 1933, access to Yosemite Valley from Wawona was improved with the completion of the Wawona Tunnel. The tunnel's power lines, its carbon monoxide sensors, and its high-speed fans made it an engineering feat. Workers used 275 tons of blasting powder and spent nearly two years drilling the tunnel at a rate of roughly 20 feet per day.
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Itineraries across USA

Acadia

Arches National Park

Badlands

Big Bend

Biscayne

Black Canyon Of The Gunnison

Bryce Canyon

Canyonlands

Capitol Reef

Carlsbad Caverns

Channel Islands

Congaree

Crater Lake

Cuyahoga Valley

Death Valley

Dry Tortugas

Everglades

Gateway Arch

Glacier

Grand Canyon

Grand Teton

Great Basin

Great Smoky Mountains

Guadalupe Mountains

Haleakalā

Hawaiʻi Volcanoes

Hot Springs

Indiana Dunes

Isle Royale

Joshua Tree

Kenai Fjords

Kobuk Valley

Lassen Volcanic

Mammoth Cave

Mesa Verde

Mount Rainier

North Cascades

Olympic

Petrified Forest

Pinnacles

Rocky Mountain

Saguaro

Shenandoah

Theodore Roosevelt

Virgin Islands

Voyageurs

White Sands

Wind Cave

Yellowstone

Yosemite

Zion