Authorities responded to the incident near the Lassen Street exit just after 6:30 a.m. The driver told the California Highway Patrol that he didn't know what shattered his passenger-side window and was not sure if it was shot out or hit by a rock.
Officers say gunfire was not the cause, but it remained unclear how the window shattered.
No one was injured, and the incident did not affect traffic for the morning commute.
