For hundreds of years, people have looked up at the hazy peaks of California's Santa Lucia Mountains at sunset and seen tall, cloaked figures staring back. Then, within moments, the eerie silhouettes disappear. These twilight apparitions are known as the Dark Watchers — shady, sometimes 10-foot-tall (3 meters) men bedecked in sinister hats and capes. One famous observer who felt the presence of the Watchers was the American author John Steinbeck. In his 1938 short story "Flight," a character sees a black figure leering down at him from a nearby ridgetop, "but he looked quickly away, for it was one...