Bridge Day commemorates the 1977 completion of which single-span arch bridge?
Bridge Day:  The event, held on the third Saturday every October, commemorates the 1977 completion of the New River Gorge Bridge. New River Gorge Bridge: The New River Gorge Bridge is a steel arch bridge 3030 ft long over the New River Gorge near Fayetteville, West Virginia, in the Appalachian Mountains of the eastern United States. New River Gorge Bridge:  With an arch 1700 ft long, the New River Gorge Bridge was for many years the world's longest single-span arch bridge; it is now the fourth longest.
New River Gorge Bridge