Hikers often stumble upon the unusual concrete structures and wonder why they were built . The ##kers directed the first air mail trucks across the US to deliver post . They lay at the tops of lit beacons and give pilots the direction to fly in to arrive at the next air field . While they are no longer used , many lie forgotten until they are found by arrow - hunting hunters .
Hikers often stumble upon the unusual concrete markers and wonder why they were built . The arrows directed the first air mail planes across the US to deliver post . They lay at the bottom of lit beacons and showed pilots the direction to fly in to arrive at the next air field . While they are no longer used , many lie forgotten until they are found by arrow-hunting fans .