The robbery happened at a 76 gas station located at 16111 Valley Boulevard in Fontana.
Authorities say the suspect entered the gas station, grabbed a case of beer, and sprayed the clerk in the face with pepper spray before fleeing Monday.
The suspect was described as a male between 19 and 20 years old, standing 5 feet tall, weighing around 150 pounds with brown eyes and brown hair. At the time of the robbery, the suspect was wearing black baggy shorts and a white T-shirt.
He is said to have fled the scene in a silver Honda Accord with tinted windows.
The victim suffered a temporary burning sensation from the pepper spray but was said to be OK.