American River
The North Fork is the longest tributary of the American River, at . It begins at an elevation of about near Lake Tahoe in Placer County at Mountain Meadow Lake, just northeast of Granite Chief and immediately due west of Squaw Valley Ski Resort. It flows westward through remote wilderness areas.
Appalachia
The effort to connect Appalachia with the outside world has required numerous civil engineering feats. Millions of tons of rock were removed to build road segments such as Interstate 40 through the Pigeon River Gorge at the Tennessee-North Carolina state line and U.S. Route 23 in Letcher County, Kentucky. Large tunnels were built through mountain slopes at Cumberland Gap to speed up travel along U.S. Route 25E. The New River Gorge Bridge in West Virginia, completed in 1977, was the longest and is now the fourth-longest single-arch bridge in the world. The Blue Ridge Parkway's Linn Cove Viaduct, the construction of which required the assembly of 153 pre-cast segments up the slopes of Grandfather Mountain, has been designated a historic civil engineering landmark.