In 1918, President Woodrow Wilson handed an airplane pilot a letter to be delivered, and airmail was officially born in the United States.
Unfortunately, reliable air navigation systems didn't start to appear until about a decade later. So how did pilots navigate then?
One of the first attempts to give pilots a hand in determining their way from town to town was to paint navigation markers on the rooftops of buildings, oil tanks and train stations.
In the late 1920s the new Aeronautics Branch in the Department of Commerce undertook the project of marking the airmail route between Los Angeles and Salt Lake City.
The 650-mile stretch was identified by the ground installation of 70-foot long concrete arrows placed at 10-mile intervals.
Each arrow was outfitted with a 51-foot tall beacon and a pair of course lights. Combined, the lights informed the pilot of direction and location.
Utah is home to several extant arrows and the giant structures are experiencing a resurgence in popularity among geocachers and flight history buffs.
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