\" \" Wikimedia Commons ( CC By-SA 3.0 One of the last vestiges of America's early transcontinental airmail beacon system, this concrete arrow still remains, in the desert outside Walnut Creek, CA. Under the direction of the Postal Service, the Airways Division of the Lighthouse Bureau created beacon stations with concrete arrows. Here's how it worked: A series of horizontal 50 to 70-foot (15 to 21-meters) long concrete arrows painted bright chrome yellow were spaced approximately 10 miles (17 kilometers) apart. Of the some 2,000 arrows that were created for the beacon system, it's estimated that about 200 remain. \"We have 126 concrete arrow photos on our homepage, two destroyed sites, six metal arrow sites and five other type arrow sites,\" says Charlotte in an email.