It's a social media scavenger hunt started by an anonymous donor who hides money in public places for others to find.
He posts clues on his Twitter page and he's already made cash drops in San Francisco, San Jose, Burbank, and Pasadena.
Now he's in Los Angeles.
The frenzy started last Friday with hundreds of people searching for hundreds of dollars hidden across the Bay Area by an anonymous man who calls himself "Mr. HiddenCash."
He puts the money in envelopes, hides them in plain sight, then uses Twitter to send out clues to find the cash. In just one week, he's amassed more than 360,000 followers.
When his clues led money-hunters to San Jose, traffic came to a standstill.
And when he brought the hunt to Southern California, local police were called in to control the cash-crazed crowds.
"This is something that's so sudden that law enforcement can't plan on it," said Sgt. Darin Ryburn with the Burbank Police Department.
CBS News' Los Angeles station KCBS found Mr. HiddenCash in a park taping money to a fountain and then sending out a clue. He agreed to an interview as long as his identity remained a secret.
"I was actually coming to L.A. for business that was not related to this and I thought, what great timing," he said. "I want to do some drops here, and get the city excited about finding money and just the idea of giving back."
He calls this "an anonymous social experiment for good," and says that after closing a six-figure real estate deal, he wanted to share the wealth. He hopes others do the same.
Stuffing birds. Bring the choppers, bring your kids, bring your friends to the beach 2mrw. This will be FUN. 11 AM. pic.twitter.com/bNFiRavqrQ— Hidden Cash (@HiddenCash) May 31, 2014
Tatianna Ramirez, 14, found $210 near a Burbank shopping mall. She's giving the money to her grandmother who's sick.
"I just really want to say, "God bless him because this is really helping my family," said Ramirez.
Now generous donors in other parts of the country are joining in.
From San Diego to Dallas to New Orleans, HiddenCash mania is quickly becoming a national phenomenon.
Mr. HiddenCash said he'll keep dropping dollars in L.A. through the weekend, and might take the hunt to New York City next month.