Michael Winter

USA TODAY

For a lucky California couple, their $10 million pot of backyard gold came with a shadow, not a rainbow.

While walking the dog last February, the couple stumbled across a treasure of 1,427 gold coins from the mid- to late-19th century buried in eight cans in the shade of a tree on their property in the state's famous Gold Country, according to Kagin's, the numismatic firm representing the anonymous finders.

Dubbed the Saddle Ridge Hoard, it is believed to be "one of the greatest buried treasures ever unearthed in the United States," the trade journal Coin Update writes.

The $5-, $10- and $20-denomination coins — uncirculated and in mint condition — have a total face value of $27,000 and date from 1847 to 1894. The majority are $20-denomination Liberty Double Eagles struck at the San Francisco Mint between 1855 and 1894, though one $5 piece came from Georgia. Experts said some might sell at auction for about $1 million.

The Professional Coin Grading Service, which certified the little mother lode, rates more than a dozen as either the finest or tied for the finest known examples of the coins, said firm co-founder David Hall.

He called the discovery "a literal time capsule" of gold coins circulating in the late 19th century.

In an interview with Kagin's, the finders, identified only as John and Mary, described how they came across their Gold Rush fortune on what they call Saddle Ridge:

John: I saw an old can sticking out of the ground on a trail that we had walked almost every day for many, many years.

Mary: I was looking down in the right spot and saw the side of the can. I bent over to scrape some moss off and noticed that it had both ends on it!

John: Years ago, on our first hike, we noticed an old tree growing into the hill. It had an empty rusty can hanging from it that the tree had grown around — that was right at the site where we found the coins… At the time we thought the can might be a place for someone to put flowers in for a grave site — something which would have been typical at the time.

There was also an unusual angular rock up the hill from where the coins were buried — we'd wondered what in the heck it was.

Mary: It wasn't until we made the find that we realized it might have been a marker: starting at the rock, if you walk 10 paces towards the North Star, you wind up smack in the middle of the coins!

Who buried them remains a mystery.

"I don't like to say once-in-a-lifetime for anything, but you don't get an opportunity to handle this kind of material, a treasure like this, ever," numismatist Don Kagin told the Associated Press.

It's rare to find such coins older than 1870, because until then paper money was illegal in California.

"It wasn't really until the 1880s that you start seeing coins struck in California that were kept in real high grades of preservation," David McCarthy, Kagin's chief numismatist, told AP.

Some of the coins will be on display this weekend in Atlanta at the American Numismatic Association's National Money Show, which runs Thursday through Saturday.

The couple, who are in their 40s and had dabbled in panning for gold, plan to keep a few coins but intend to sell most on Amazon. Mary said they'll use the proceeds to retire debts and help "people in our community who are hungry and don't have enough to eat," along with the arts and "other overlooked causes." They don't plan to change their lifestyle and hope everyone will treat them the same as always.

Mary offered one priceless piece of wisdom.

"Whatever answers you seek, they might be right at home!" she said. "Don't be above bending over to check on a rusty can!!!!"