The Los Angeles County Sheriff's Department says the incident occurred just before dawn Saturday on Interstate 5 near Templin Highway in Castaic, where the officer's car was involved in a collision.
During a subsequent struggle, the other driver used the officer's handgun to shoot him.
The Sheriff's Department says the officer's injuries were not life threatening. His name was not released.
The gun has not been recovered, and no description of the suspect or his vehicle was released.
An investigation is ongoing.