A pickup truck carrying pest control chemicals was reported to be on its side at about 5:15 a.m., blocking east and westbound lanes of Highway 12, CHP officer Ralph Caggiano said.
The driver was uninjured in the single-vehicle crash, Caggiano said.
A hazardous materials response crew has been called to the scene where pesticide has reportedly spread across to the roadway.
CHP officers and Caltrans have shut down the highway between Red Top Road and Interstate Highway 80.
Drivers are being diverted alternate routes, Caggiano said.
A Sig-alert was issued at 5:36 a.m.