Last year, a couple walking the usual route around their California gold-country property happened upon a can sticking out of the ground. They pulled it out and uncovered seven others, all filled with hundreds of U.S. gold coins.

Experts announced the find last month after a year of work researching and authenticating the 1,427 coins, worth an estimated $10 million.

But the origin of the Saddle Ridge hoard remains a tantalizing mystery, one that has coin buffs and amateur sleuths on the case. Though such discoveries are not unheard of in Europe, buried caches in the United States are less common.

“But 1,400 coins, all gold? That’s spectacular,” said Douglas Mudd, museum curator for the American Numismatic Association.

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At one of the association’s national coin conventions last month in Georgia, a display sample of the collection was the topic of conversation. All kinds of romantic notions come attached to this type of buried treasure, “the escaping outlaw, the eccentric miner or millionaire that decided to save their money that way,” Mudd said.

In the days after the discovery was announced, many coin buffs believed the fortune was tied to a theft more than a century ago.

In 1901, $30,000 in $20 coins was discovered missing from the San Francisco Mint. The coins were never recovered, and Chief Clerk Walter Dimmick served time in San Quentin prison for the theft.

The coins discovered by the anonymous couple, dated between 1847 and 1894, mostly consist of $20 pieces and have a face value of nearly $28,000.

The timing, the value — it all seemed right.

But the U.S. Mint has found no link between the Saddle Ridge treasure and any Mint thefts, spokesman Adam Stump said.

Experts from Kagin’s, which evaluated the hoard and is representing the couple, said the theory had problems from the start.

Each bag in Dimmick’s cache would have contained pieces with the same date and mint mark, but the treasure discovered last year contains a mix of coins with 72 distinct date and mint mark combinations, said David McCarthy, senior numismatist for Kagin’s.

Another theory suggests the coins date back to the secretive, subversive Confederate group the Knights of the Golden Circle, believed to have buried and protected treasure in a dozen states.

Though they could be the buried fortune of a businessman, the time period, markers near the cache and manner in which the coins were buried fit the mold of the knights, said Warren Getler, a former Wall Street Journal reporter. He co-wrote “Rebel Gold,” which argues the group was active decades after the Civil War.

Some hopefuls have come forward to claim the coins belong to ancestors.

“They’re all over, stashes that turn up, but nobody says a word,” said Mead Kibbey, a historian in the Sacramento area. “The thing is, in any well-appointed home in the mountains, there’s a metal detector. Right next to the umbrella and the shotgun behind the door, they’ve got a metal detector.”

Experts at Kagin’s did extensive research to determine whether the coins were ill-gotten. Despite hearing from quite a few people, the firm has received no credible claims to the coins and does not expect to, McCarthy said.

The most plausible explanation, he said, is that the stash was buried over many years by someone hoping to keep their fortune safe.

The couple said they walked the route for years before uncovering the cans. They were so shocked by what they found that they took the coins, placed them in an old ice chest and reburied them in their wood pile.

Thirteen of the pieces are the finest of their kind, experts said. One, an 1866 $20 piece made in San Francisco and missing “In God We Trust,” could bring $1 million on its own, according to David Hall, co-founder of Professional Coin Grading Services, who recently authenticated the coins.

The y will be sold on as early as May, McCarthy said.