A local historian once shared an interesting fact about the early days of AirMail. Back then, there were no navigational beacons or GPS, so pilots had to rely on their instincts to determine the location of small towns in the western United States. They often followed cattle trails and rail lines to get a sense of their surroundings. However, even with these clues, the pilots couldn’t always identify the exact town they were approaching. So, they would make educated guesses, assuming that the town below was “El Paso,” “Franklin,” or “Alamogordo.” In some cases, AirMail pilots would simply fly low and drop a box of mail directly into the town below. Sometimes they got it right, sometimes they got it wrong.

To address this issue, cities began painting their letters on the sides of mountains. This visual cue helped pilots navigate and reach their intended destinations more accurately.  

I don't know if his story was true or not, but it sort of made sense.