An assistant manager spotted the backpack abandoned in a booth, ABC's San Francisco station KGO reported. She called the restaurant owner, who opened the bag up to look for ID and found the cash.
"I open the zipper, I see lots of money, cash money, $100 bills stack up like half the bag," owner Altaf Chaus told the station.
"I said, 'Wow! Today's my birthday, this is my birthday gift!'" he added, joking.
But Chaus called the police instead.
"I don't want that money. Maybe it belongs to somebody," he said.
They're working with the bank to find out who the cash belongs to, the station reported.