The debris, described as a 3-foot-long piece of metal, was first reported near the High Street off-ramp at 5:41 a.m.
Initial reports to the CHP indicated that one car, a black Mercedes, had damage to its undercarriage and was leaking oil.
Altogether, 13 motorists reported damage to their cars, CHP Officer Ron Simmons said.
"Some of them had flat tires, some of them had damage to the body," he said.
The CHP believes the metal debris fell from a truck and they're searching for that vehicle.
ABC7 News contributed to this story.