But he and an accomplice were captured in Irwindale and both were being treated to incarceration in the West Valley Detention Center in Rancho Cucamonga, authorities said.
The robber walked into the ampm mini mart at 8127 Mulberry Ave. about 8:30 p.m. and threatened to shoot the clerk if she didn't empty the cash register.
Still wearing the Halloween mask, he ran out of the store with an undisclosed amount of money and fled in a vehicle driven by a second man, police said.
A witness reported the license plate number of the car to police, who determined the vehicle was registered in Los Angeles County. Officers broadcast the information to other law enforcement agencies.
Undercover Fontana officers spotted the vehicle on the 10 Freeway and followed it to Irwindale where they arrested two men, identified as Andres Jimenez and Jose Segura, both 19, on suspicion of armed robbery. Their cities of residence were not not known.
"Detectives are inquiring with surrounding cities to find out if the suspects' methods of operation are similar to any incident in other areas," said Fontana a police spokesman, Sgt. Robert Morris. "This is still an ongoing investigation."