The Mojave Megaphone, sometimes called the Sentinel Enigma, has been a mystery for decades. It sits high on a rocky ridge in one of the most remote parts of the Mojave Desert. This odd, welded-steel structure looks out over the empty landscape, and no one knows who built it or why. Some people wonder if it was part of a railroad warning system, a military sound monitor, or a surveying tool lined up with desert landmarks. Others even believe it might have been used to communicate with UFOs. But a rare clue from a 1990 Desert Dispatch newspaper article may...