Giant Concrete Arrows That Point Your Way Across America (2013)
cntraveler.com
cntraveler.com
And who were the poor souls that had to drive up to these generators and fill them with diesel every so often? These things couldn't have been off major roads so I imagine this meant a lot of off-road driving. Considering this spanned the nation, the number of staff involved in just keeping the lights on must have been significant.
The article is probably wrong about this replacing the Pony Express. By the 1920s long distance mail was sent via train. I can't imagine the post office still using horses for long hauls.
Wikipedia has more info:
https://en.wikipedia.org/wiki/Transcontinental_Airway_System
>The beacons flashed identification numbers in Morse code. The sequence was "WUVHRKDBGM" prompting the training phrase "When Undertaking Very Hard Routes Keep Directions By Good Methods." to remember the sequence
I find this part fascinating. More info here:
The article points out that air mail was 60 years after the Pony Express. The Pony Express only operated for 19 months before the Civil War, it would be the very confused author who thinks anything in the 1920s replaced the Pony Express.