“If you’re wandering the barren landscape of Utah or Nevada and stumble across a massive, firmly-grounded concrete arrow, rest assured, aliens have not been marking a path through the United States. Forming a line across the country, these decaying markers are actually remnants of the Transcontinental Air Mail Route, a revolutionary system connecting both coasts over 90 years ago to facilitate speedy mail delivery. But given that the full path is only visible from an aerial view, like the Peruvian Nazca lines, their strange appearance has puzzled many hikers and ranchers who have stumbled across a lone, giant arrow.”

– http://www.thedailybeast.com/articles/2013/12/19/the-strange-arrows-that-point-the-way-across-america.html