Dotting the American landscape — from San Francisco to New York — is a series of 70-foot concrete arrows left behind from the early days of transcontinental mail delivery.

Set into hillsides or lying flat on scrubby desert land, the arrows once guided pilots across the country so they could transport mail.

On Aug. 20, 1920, the U.S. opened its first coast-to-coast airmail delivery route using Army surplus planes leftover from World War I, and many of the planes were even piloted by veterans.

However, there were no decent aviation charts or flight-planning implements, so pilots had to navigate their way using landmarks. This made flying in poor weather conditions difficult and flying at night nearly impossible.

Congress agreed to fund the world’s first ground-based civilian navigation system, the Transcontinental Airmail Route, in 1923, and construction began on a series of lit beacons that would extend across the country.

Bright yellow concrete arrows were built every 10 miles, and each arrow was situated next to a 51-foot steel tower lit by a rotating beacon of light.

Transcontinental Airmail Route map

By 1924, the line of illuminated arrows stretched from Rock Springs, Wyo., to Cleveland, Ohio, and by 1929 it spanned the continent. Pilots could now transport mail in about 30 hours instead of a matter of weeks.

However, as advances were made in communication and navigation technology, the massive arrows became obsolete. The beacons were decommissioned in the 1940s, and most of the steel towers were torn down and recycled as scrap metal to support the war effort.

Few of the towers remain today, but preservation program Passport In Time has prevented three sites from falling into disrepair. One in Elko County, Nev., has been repurposed and is now a TV antenna.

And although they’re now bleached from the sun and covered in weeds, hundreds of arrows still exist, pointing a 2,629-mile route from the Atlantic to the Pacific.

concrete arrow on Google Maps

Photos: Google Maps

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Laura Moss writes about a variety of topics with a focus on animals, science, language and culture. But she mostly writes about cats.

What was the purpose of these giant, concrete arrows?
Hundreds of 70-foot, bright yellow arrows once guided pilots across the U.S., and many of them still exist today.