The Columbus Ledger-Enquirer reports the incident happened about 1 p.m. on U.S. 27 in Troup County between Old Chipley Road and Smokey Road, said Sgt. Chad Mann, a Troup County Sheriff’s Office spokesman.
The car was headed north behind a Bush Hog mower operated by the Georgia Department of Transportation, according to the Troup County Sheriff’s Office.
The rock grazed the front passenger across the lips, Mann said, before striking the woman in the back seat and killing her instantly.
The victim, whose name was not released, was pronounced dead at the scene.
"It's just a sad day," Mann said.