The Great Diamond Hoax of 1872: How Two Kentucky Cousins Fooled San Francisco’s Richest Men
Imagine you’re a banker in San Francisco in 1872.
You survived the Gold Rush. You made good money off the Comstock silver boom. Everybody in town thinks you’re one of the sharpest guys in California.
Then one night, two rough-looking prospectors walk into a mine broker’s office with a leather sack full of uncut gems.
“Diamonds,” they say. “From a field out West. Can’t tell you where.”
Within two years, men just like you will pour the equivalent of millions of dollars into that secret field.
And when the whole thing falls apart, newspapers will call it “the most gigantic and barefaced swindle of the age.”
This is the Great Diamond Hoax of 1872, and honestly, it’s one of my favorite cons in American history.
Two cousins and a bag of gems
The whole thing starts with two cousins from Kentucky: Philip Arnold and John Slack.
Neither guy was rich. Neither one was famous. They were just a couple of former gold miners who had spent years bouncing around the West trying to catch a break.
By 1870, Arnold had a regular job in San Francisco. He worked as an assistant bookkeeper for a company that made diamond-tipped drill bits. Every day, he was around cheap industrial diamonds—little rough stones nobody thought much about because they were used for drilling, not jewelry.
Arnold started reading about diamonds in his spare time. And at some point, he started quietly pocketing some of those stones.
Those cheap little rocks were about to become the center of one of the craziest scams in Western history.
Now, if you’ve never heard of the Great Diamond Hoax before, don’t feel bad. Most people haven’t. But here’s why the scam worked.
By the early 1870s, people out West had already watched fortunes show up out of nowhere. Gold had done it. Silver had done it. Word was also coming in from South Africa that real diamond fields had been found there.
So when somebody said there might be diamonds in America too, it didn’t sound crazy. It sounded like the next big thing.
Newspapers ran with every mining rumor they could find. Old-timers told stories about gems laying around in the wilderness. A few stray diamonds had even been found in California rivers during the Gold Rush.
Arnold and Slack looked at all of that and basically thought: everybody already wants to believe this. So what if we just make it look like we found them?
The leather sack trick
In late 1870, Arnold and Slack walked into the office of a San Francisco mine broker named George D. Roberts.
They looked exactly like what they were trying to look like: dusty, tired, believable. The real deal.
They told Roberts they had struck something big out in “Indian country” somewhere and asked if they could leave a leather bag in his safe overnight. They claimed they had tried to get to the Bank of California, but had shown up after closing.
Roberts asked what was in the bag.
Arnold hemmed and hawed a little, then “accidentally” let it slip: rough diamonds.
He made Roberts promise not to look inside.
Of course Roberts looked.
The bag was full of uncut diamonds, rubies, sapphires, and other gems.
And what is a mine broker going to do when he thinks he just stumbled onto the discovery of the century?
He runs straight to William Chapman Ralston.
Ralston founded the Bank of California. People called him the “Magician of San Francisco.” He had his fingers in factories, water systems, theaters, and the Comstock silver business. If Ralston believed something was real, other people paid attention.
Arnold never had to go around bragging about a diamond discovery. He left a bag in the right safe and let other people do the talking for him.
How they sold a fake diamond field
Ralston pulled in more heavy hitters. A promoter named Asbury Harpending heard about the story while he was in London and hurried back to get in on the deal. Investor William Lent signed on. Other wealthy men and Civil War veterans started circling the supposed diamond field.
Everybody wanted a piece of it.
Meanwhile, Arnold and Slack kept playing the same act: two humble prospectors who would honestly rather be left alone. They said the field was dangerous, way out in Indian territory, and hard to get to. They acted uncomfortable around the money, lawyers, and paperwork.
And the more they acted like they didn’t want it, the harder the rich guys chased them.
The investors wanted proof. Not just a bag of gems—an actual field.
So Arnold and Slack said they were going back out to bring home more samples.
Instead, they sailed to London under false names and bought about £20,000 worth of cheap, low-grade rough diamonds and rubies from a dealer named Leopold Keller. These were not jewelry-store diamonds. They were industrial-grade stones sold by the pound.
Then the cousins headed to a remote stretch of high desert near the Colorado–Wyoming border.
Nobody lived out there. Nobody was watching.
They salted the field.
They pushed diamonds into anthills. They stuffed rubies under rocks. They scattered gems across the surface like somebody spilled a bag of trail mix.
If you kicked around in the dirt for a few minutes, you were going to “find” diamonds almost anywhere.
They brought samples back to San Francisco, and the investors went nuts.
The group hired a respected mining engineer named Henry Janin. Janin had reportedly inspected more than 600 mines in his career without a major mistake. When he said something was real, people listened.
Janin went to the site with investors and the two con men. Of course, he found exactly what Arnold and Slack had planted for him to find.
He came back convinced the field could produce a million dollars a month.
At that point, as far as the investors were concerned, the diamond field was official.
Tiffany says yes
Some of the stones made it to New York and ended up on the desk of Charles Lewis Tiffany.
Yeah, that Tiffany—the founder of Tiffany & Co.
Here was the problem: Tiffany and his people knew polished, cut jewelry. They did not know rough industrial diamond gravel. But they looked over the bag, did some quick math, and decided the stones were worth about $150,000.
They were way off. Badly off.
But nobody cared much about that part. The Tiffany name was what stuck in everyone’s head.
Now the investors had Henry Janin saying the field was real, Charles Tiffany saying the stones were valuable, and a secret location nobody else could easily check.
They stopped wondering whether the deal was big. They started wondering how fast they could get in.
A company formed: the San Francisco & New York Mining and Commercial Company.
It raised about $2 million. The investors included Ralston, Harpending, Lent, Congressman Benjamin Butler, and former Union general and one-time presidential candidate George McClellan. Money from Europe was sniffing around too.
Arnold and Slack agreed to cash out their interest for hundreds of thousands of dollars plus stock.
By the time it was all said and done, two Kentucky cousins with no education and no powerful connections had walked away with a fortune. Different sources put their haul anywhere from around $8 million to more than $10 million in today’s money.
They had made some of the richest, smartest men in the country look like they had never seen a con before.
Clarence King sees the problem
Except there was one problem.
If the diamond field was really where Arnold and Slack said it was, it sat smack in the middle of territory a young government geologist had spent five years surveying.
And he was dead certain there were no diamonds out there.
His name was Clarence King.
King was 30 years old, Yale-educated, and kind of a real-life adventurer type. He had been leading the Geological Exploration of the Fortieth Parallel, mapping minerals, plants, and everything else across a massive stretch of the West.
If there really were diamonds in his survey territory and he had missed them, it would have been the biggest screwup of his career.
He didn’t take that well.
The whole thing began to fall apart almost by accident. One of King’s men, Samuel Emmons, was riding a train near Oakland and happened to run into Henry Janin. Janin proudly showed him some of the gems from the field.
Something about it didn’t sit right with Emmons.
He told King that the supposed diamond field was inside King’s survey area.
King tracked Janin down in San Francisco, grilled him for details, and used that information to figure out roughly where the secret field had to be.
Then King and a small crew rode five brutal days into the high desert.
They found the site.
And yes, there were diamonds there.
But King was not looking at the sparkle. He was looking at how the stones sat in the ground.
The first thing that jumped out at him was the ratio. For every diamond, there were about twelve rubies. Nature doesn’t scatter diamonds and rubies around in a neat little mix like that. That isn’t a natural deposit.
Then he noticed the gems were right near the surface. In anthills. Under little rocks. In the top couple inches of dirt.
Real diamond deposits go deep. Dig down at this site and you got nothing.
Then came the one thing that sealed it.
One of King’s men picked up a stone with polish marks from a cutting wheel.
Somebody had cut that gem and then buried it in the dirt.
At that point, King knew exactly what he was looking at.
The whole diamond field was a set piece.
Somebody had built it on purpose.
The Great Diamond Hoax is exposed
King rode back to San Francisco and asked for a meeting with the big investors.
On November 11, 1872, he laid it all out: the impossible mix of gems, the shallow stones, and the polished gem sitting in the dirt.
There was only one explanation.
It was a fraud.
The company folded fast and handed back whatever money was left.
Then the story hit the newspapers.
The San Francisco Chronicle ran a major November 26, 1872 story with a stacked headline beginning: “Unmasked! The Great Diamond Fiasco.” The paper called it a mammoth fraud and explained that the field had been salted.
San Francisco’s financial elite—guys who genuinely thought they were too smart to ever get taken—had just been schooled by two cousins from Kentucky.
What happened to everybody?
Ralston reportedly lost around $250,000 of his own money. A few years later, after other financial disasters piled up, he was found dead in San Francisco Bay.
Henry Janin’s spotless reputation was done. He never lived the diamond-field mistake down.
Benjamin Butler was publicly embarrassed for being tied to the whole mess.
And the other investors licked their wounds and moved on.
Philip Arnold was already back in Kentucky, sitting pretty in a nice brick house and running his own bank. California tried to drag him back to face charges, but Kentucky was not interested in cooperating.
Eventually, Arnold settled some lawsuits and handed back a chunk of the money—but he kept plenty.
A few years later, he got shot during a fight with a business rival. He survived the shooting at first, but came down with pneumonia while recovering and died in 1879. Not in prison. Not broke. Just gone.
John Slack basically disappeared. From what researchers can tell, he ended up in New Mexico working as an undertaker, living a quiet life after helping pull off one of the biggest frauds of the century.
Clarence King was the one person who came out ahead reputation-wise. He became the first director of the United States Geological Survey.
The strange final twist: real diamonds nearby
The exact place where Arnold and Slack salted their fake diamond field is still debated.
But here’s the weird part.
About a hundred years later, geologists really did find diamonds in the broader Colorado–Wyoming border region. Not at Arnold and Slack’s fake field, but close enough to make the story even stranger.
In the 1990s, a real diamond mine called Kelsey Lake opened near the state line. It produced actual diamonds, including a stone that weighed more than 28 carats.
The mine shut down in 2001, but the twist is still pretty great.
The American diamond field that fooled San Francisco was fake.
But there really were diamonds out there after all.
What do you take away from this?
Honestly, Arnold and Slack didn’t fool a bunch of idiots.
Ralston was one of the biggest names in San Francisco. Janin was supposed to be one of the best mining engineers in the country. Tiffany was Tiffany.
But everybody wanted the diamond field to be real so badly that nobody stopped and asked the most basic question:
Why are diamonds and rubies sitting together in the top couple inches of dirt?
Arnold and Slack didn’t need fake diamonds.
They had real ones.
They just needed people with money to believe those diamonds came from the ground.
Ricky’s Historical Tidbits is about the strange people, places, and events that textbooks skip over or barely mention. If you liked this story, share it with someone who’d get a kick out of it, check out the other articles and episodes, and subscribe for more California, Gold Rush, Old San Francisco, and Western history.
