Concrete arrows in the desert

In the late 1920s and early 1930s, the new Aeronautics Branch in the Department of Commerce established a 650-mile air route from Los Angeles to Salt Lake City to carry mail...

Large concrete arrows were constructed on the ground along the way as visual navigational aids for the planes flying the mail route. There were built at intervals of approximately 10 miles and were about 70 feet long. Typically, there was a 51-foot beacon tower in the middle of the arrow topped with a powerful rotating beacon light. Below the rotating light were two course lights pointing forward and backward along the arrow. The course lights flashed a code to identify the beacon's number...

The concrete arrows are all that remain today. 

From the Washington County Historical Society, via Reddit.