U.S. Route 12 is a major east–west U.S. Highway, running from Aberdeen, Washington, to Detroit, Michigan. It spans 430.5 miles (692.8 km) across the state of Washington, making it the second longest highway in the state. It is also the only numbered highway to span the entire state from west to east, starting near the Pacific Ocean, and crossing the Idaho state line near Clarkston. It crosses the Cascade Range over White Pass, south of Mount Rainier National Park. Portions of it are concurrent with Interstate 5 (I-5) and Interstate 82 (I-82), although the majority of the route does not parallel any interstate highway.

White Pass is a mountain pass in the northwest United States, in the Cascade Range of Washington, southeast of Mount Rainier and north of Goat Rocks. U.S. Highway 12 travels over White Pass, connecting Yakima County on the east with Lewis County. It was named after Charles A. White, a surveying engineer who led the party that discovered it for the Northern Pacific Railroad in 1878.