The San Jose man hit the jackpot when he realized that a storage unit he'd bought in a blind auction contained thousands of dollars worth of rare coins and solid gold and silver, reported ABC News.
The man, who wishes to remain anonymous, had paid $1,100 for the unit.
The contents of the container - 16 gold doubloons, several silver Spanish dollars and gold and silver ingots, according to the San Francisco Chronicle - have all been authenticated by appraisers.
The unit previously belonged to an elderly woman who died recently, said Laura Dotson of American Auctioneers, the company that sold the unit.
Elderly owners are often a sign that a unit is likely to contain collectibles, John Cardoza of Storage Auction Experts told ABC:
"What some people do is, they look at the names. If it's Ethel or Myrtle, it sounds older."
There is a growing art to storage unit auctions, in which customers place bids on units whose owners haven't paid rent for at least three months. Clients are usually allowed a brief look through the unit's door before they bid, but rely largely on guesswork to judge what the contents are and whether they're worth buying.
Things to look out for include cobwebs - indicating that the unit's contents have not been recently cleared out - well-organised stacks and good quality boxes, according to some of the storage auction veterans featured on NPR's This American Life radio show.
But ultimately it comes down to sheer luck whether you end up with treasure or trash.
In the case of this lucky buyer, he was first attracted to the unit for more practical reasons. All he really wanted was the large plastic container at the front of the unit, Dotson told ABC News:
"He said he like it was in [plastic] and clean and easy to move."
That handy plastic box was the very thing in which the unit's previous owner had chosen to stash her treasure.