Man tries to hold up Rohnert Park car wash with potato chip bag

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Authorities are warning businesses in Rohnert Park, in an area along Rohnert Park Expressway near Highway 101, to take caution after a man wielding a potato chip bag and alleged handgun attempted to rob a car wash there Friday evening.

The suspect first approached a female cashier at KaCees World of Water car wash at 320 Rohnert Park Expressway on Friday at about 7:48 p.m., carrying a potato chip bag, according to a statement from Rohnert Park’s Department of Public Safety.

The man ordered the cashier to fill the potato chip bag with money, warning her that there was a gun inside the bag, according to the statement.

However, the cashier saw through the suspect’s act, the statement said. She realized the bag held only a piece of cardboard and determined the man had no gun.

The cashier then called out to a fellow employee in the parking lot for help. The other employee approached the suspect, sending the man fleeing in a car, heading south on Redwood Drive without money or property, according to the statement.

The cashier waited about 10 minutes before calling the police, officials said in the statement.

The Sonoma County Sheriff’s Office and Cotati Police Department helped in the search for the would-be robber. As of Saturday morning, the suspect remained on the loose.

The suspect was described as black man in his 30s or 40s, 5-foot-8-inches to 5- foot-11-inches tall with a stocky build. He was reported wearing a black baseball hat, black sweatshirt and dark pants. He was also, according to the statement, unshaven with gray stubble.

Officials ask anyone who sees someone matching the suspect’s description to call the Rohnert Park Department of Public Safety at (707) 584-2600.

Kevin Schultz is a San Francisco Chronicle staff writer. Email: kschultz@sfchronicle.com Twitter: @KevinEdSchultz