Fifty tourists a year get lost in Joshua Tree National Park and find their way back out. In 2010, 66-year-old Bill Ewasko went in and never came out. For The New York Times Magazine, Geoff Manaugh follows the eight-year search for Ewasko and the men who obsessed about finding him.

Search-and-rescue experts have developed lost-person-behavior algorithms to track missing hikers. They use cellphone pings to create a map and timeline, and use past behavior to try to guess their target’s behavior. Technology has also turned amateurs into sleuths and spun web forums devoted to missing people. We live in what Manaugh calls “a golden age for amateur investigations.” For some, missing persons cases become a hobby, a puzzle to solve, a form of salvation, even when wilderness areas thwart their techniques.

To hear Marsland tell it, his inaugural trip to the park, on March 1, 2013, bore the full…

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