In the early 1920s, the US Postal Service faced a major bottleneck: airmail was fast by day, but cross-country routes stalled at sunset because pilots had no reliable navigation instruments for night flights or fog.
so to solve this, government constructed the Transcontinental Airway System a physical visual highway stretching from New York to San Francisco 50 foot concrete arrows: Poured directly into the ground and painted bright chrome yellow to point pilots along the exact flight corridor. Rotating gas beacons: Placed atop 50-foot steel skeletal towers mounted at the center of each arrow, flashing distinctive Morse codes every 10 miles.
Small concrete shacks housing automated generators and fuel supplies stood at the tail of each arrow. Pilots would fly from one flashing beacon to the next, checking the physical orientation of the arrow beneath them to stay on course. Within a decade, radio navigation and radar rendered the visual airway obsolete, leading to the decommission of the towers. However, hundreds of these massive concrete arrows remain preserved on remote hillsides and desert terrain across the American West today.
Full write-up detailing the route maps, logistics, and surviving markers: https://thehistoricalinsights.page/2026/07/giant-concrete-arrows-america-before-gps.html