An Audi pulled in front of his car and blocked him, men exited the car, smashed open his back window and brandished a knife, Lorenz said.
The men demanded the bag, which he said contained "a considerable amount of cash."
An employee at the gas station told a News-Press photographer that it contained $50,000 to $60,000
The men fled in a silver or gray Audi, Lorenz said. The owner was not injured, he added.
Monday's robbery was the second in the last four days.
The two robberies would push this month's total to four, according to the Glendale Police Department.
Police are also requesting the public's help in finding an armed robber who stole about $500 on Friday from a Chinese restaurant, Lorenz said.
He gave the restaurant clerk at Wong's Wok, 1415 E. Colorado St., a credit card to pay for his meal, but the card was declined, Lorenz said.
That's when he reached into his waistband and pulled out a handgun, Lorenz said.
The man pointed the gun at the clerk's head while grabbing money from the open drawer, he said.
"The employees ran in fear of their life toward the back of the restaurant," Lorenz said.
The man ran from the restaurant on Colorado Street, he added.
The man was described as 5 feet 9 inches tall, 160 pounds and 25 to 30 years old. He was wearing a long-sleeved, blue-striped shirt.
Anyone with information on the robberies may call the Robbery-Homicide Unit at (818) 548-3487. To remain anonymous, call the Los Angeles Regional Crime Stoppers' tip line at (800) 222-TIPS.