Like the people who hike it, the Appalachian Trail is always moving.

Technically, Tuesday marks the 75th anniversary of its completion. But the 2,180-mile path stretching across 14 states from Springer Mountain, Ga., to Katahdin, Maine, is never really finished.

It took 15 years for hundreds of volunteers, state and federal partners, trail maintenance clubs and young workers with the New Deal-era Civilian Conservation Corps to build the original path. In the decades since, nearly 99 percent has been relocated or rebuilt, and transferred from private to public ownership.

That means the trail and some 250,000 contiguous acres are better-protected than ever from development and suburban sprawl....