IN THE mid-19th century, hundreds of thousands of Americans flocked west in search of gold. Today those with an appetite for treasure head to the Rocky Mountains, where Forrest Fenn, an octogenarian art collector, claims to have hidden a bronze box containing gold coins, Chinese jade, emerald jewellery and other riches, including two gold nuggets “as large as chicken eggs”. Mr Fenn first had the idea to stash away the treasure nearly 30 years ago, when he was diagnosed with aggressive kidney cancer and told his chances were slim. Over the decades he spent hawking art to the likes of Steve Martin, an actor, and former President Gerald Ford from his gallery in Santa Fe, New Mexico, Mr Fenn had built up an enviable personal collection of art and artefacts. He decided to pack as much as he could carry and hike to his favourite spot to die. The only way to track him—and his cache—would be to solve the riddle he would leave behind.

Mr Fenn’s cancer later vanished, but the idea of hiding the treasure continued to grip him. “When I hid my treasure about six years ago, this country was in a deep recession…I wanted to give some hope to those who were willing to search for the treasure,” Mr Fenn explained, sitting in a study lined with shelves crammed with Kachina dolls, beaded moccasins and fore-edge painted books. In 2010, without alerting his wife or daughters, Mr Fenn slipped into the mountains north of Santa Fe, where he lives in an estate of adobe houses, and deposited the bronze box “where warm waters halt”. In his memoir “Thrill of the Chase”, which was published later that year, he wrote a six-paragraph poem said to contain nine clues indicating where the treasure lies. It concludes: “So hear me all and listen good, your effort will be worth the cold. If you are brave and in the wood I give you title to the gold.”

Based on the number who have contacted him, Mr Fenn estimates that up to 100,000 people have thronged to the Rockies in search of his hidden cache over the past six years. Some “Fenn-atics” like Cynthia Meachum, a pensioner who lives in Albuquerque, search almost full-time. Others are more nonchalant about their questing, using Mr Fenn’s poem more as a way to give their outdoor exploits a sense of purpose.

Eager to capitalise on interest in Mr Fenn’s hidden bounty, the state of New Mexico included the art dealer in one of its promotional videos (it has been viewed 400,000 times on YouTube). Last year the mayor of Santa Fe established a “Thrill of the Chase” day, and in June the city helped promote “Fenn-boree”, a weekend-long conference for treasure-seekers. In addition to a potluck dinner and Fenn trivia, the gathering featured something almost as exciting to hunters as ferreting out the coveted bronze box: a cameo appearance by Mr Fenn himself.