A 30-year-old Santa Rosa woman, who police said was speeding through Petaluma with her infant unsecured in the back seat of her car, was arrested Thursday night on suspicion of DUI and felony child endangerment, Petaluma police said.

Stacie Loomis was arrested just before midnight Thursday after a police officer said she saw Loomis driving a Volvo station wagon north on Petaluma Boulevard near Industrial Drive at speeds topping 60 mph. The posted speed limit in that area is 45 mph.

K-9 Officer Corie Joerger, who pulled Loomis over, said she saw the woman’s 4-month-old son lying face down in the back seat of the car. There were two car seats in the Volvo, according to Joerger, but the child was not secured into either one.

Loomis reportedly told Joerger that she thought the child’s father had put him into one of the car seats.

Loomis was booked into Sonoma County Jail on $50,000 bail. She has a court date scheduled on Monday, according to jail records. Petaluma police said the child was released to his father.

You can reach Staff Writer Elizabeth M. Cosin at 521-5276 or elizabeth.cosin@pressdemocrat.com.