A CHP truck was one of four vehicles involved in a chain reaction crash that tied up traffic on Interstate 5 in Tehama County Wednesday morning.
Southbound traffic was reduced to one lane in the Cottonwood area, just south of Redding.
The collision happened just after 6:30 a.m. Wednesday.
Officers said a yellow vehicle was northbound when it crossed the center divide and into oncoming traffic. The yellow vehicle struck another car.
The driver of a Nissan pickup truck tried to avoid the initial crash, but collided with a CHP truck.
Four people suffered moderate to minor injuries.
As of 9 a.m., southbound traffic remained reduced to one lane.