The accident happened at about 7:30 a.m. on westbound Highway 4 near Somersville Road and involved either rebar or a retaining wall, CHP Officer Tom Maguire said.
Caltrans is managing a highway widening project in the area, Maguire said.
The workers suffered minor injuries and were transported to John Muir Medical Center, Maguire said.
The California Division of Occupational Safety and Health responded to the scene and is handling the investigation into the accident, he said.
Maguire said the accident was not impacting traffic in the area as of shortly before 8:30 a.m.