The remnants of Transcontinental Air Mail Route Beacon 37A, which was located atop a bluff in St. George, Utah. (Photo: Dppowell/Wikipedia) Across the United States, from Los Angeles to New York, lies a network of mostly forgotten infrastructure, a system that was obsolete before it was ever finished—forgotten relics from the early days of powered flight. … … … The concrete arrows, and some of the towers and sheds, still stand today. The state of Montana actually continues to use the system to help pilots navigate the rugged peaks of the region, as mountainous terrain can interfere with more sophisticated technological systems. Around nineteen of them are still in use. Here’s a handy map of some of the surviving locations of these nearly-obsolete stone aviation arrowheads.