To show its appreciation, the Yellow Checker Star cab company named him its "Driver of the Year" and also handed him a $1,000 cash reward.
According to Friday's edition of the Las Vegas Sun newspaper, Gamboa, who has worked 13 years for the cab company, picked up a passenger at the Cosmopolitan casino and drove him to the Palms Place hotel and spa, a service that earned him a $5 tip.
Gamboa then headed for another casino, the Bellagio, where a doorman saw the forgotten package in the back seat of the taxi as he opened to door for another passenger to get in.
The doorman put the package in the front seat, never imagining that brown paper bag would contain anything important.
"I told my passenger, 'You are my witness on this,' and then I immediately called my dispatcher," Gamboa said, after discovering that the bag contained a fortune in cash.
Yellow Checker Star immediately contacted local authorities to see if they could identify the passenger, which they did several hours later.
The forgetful passenger was a 28-year-old professional poker player who asked to remain anonymous.
When he picked up the money, the gambler asked to meet Gamboa in order to thank him personally and ask for his contact information so he could reward him with a check for $10,000.
"I just wanted to do the right thing," Gamboa said.
For his part, the field operations manager of Yellow Checker Star, Joel Willden, said that this was the largest amount of money found in a cab since this taxi business began 30 years ago.
"He's absolutely awesome; he's one of our stars," Willden said about Gamboa.