The CHP has received 14 reports of cars being hit by rocks since mid-January, 10 of which were in the last week, Maguire said.
Most of the vehicles have been hit between 7 p.m. and 2 a.m. in both north- and southbound lanes of the highway between Railroad Avenue and Bailey Road.
The rocks have varied in size, but some have been large chunks of concrete, and appear to have been tossed blindly over the wall, Maguire said.
So far, the rock throwers have not caused any physical injuries to drivers, but they have caused significant damage to vehicles, including body damage, shattered windshields and tire damage, Maguire said.
The CHP is working with Pittsburg police and the California Youth Authority to identify the people involved. Maguire said investigators have some photographs of the people they think have been throwing the rocks, but are not yet releasing those photos to the public.
If caught, the rock throwers could face fines, misdemeanor charges and civil lawsuits filed by the victims.
Anyone with information about the case is asked to call the Contra Costa area CHP at (925) 646-4980. Anyone who sees someone in the act of throwing a rock should call 911.