40 Most Impressive Engineering Feats in U.S.

When engineers figured out how to force the Chicago River to flow in a different direction, that's a feat. When they spanned the Pacific Ocean in San Francisco with the Golden Gate Bridge, that's a feat. Or even when engineers carved precise measurements into hillsides with rudimentary tools—whether for a road or a monument—that's a feat. Explore 40 of the most impressive engineering feats in American history.