The big rig overturned shortly before 8 a.m. at North Mathilda Avenue, spilling vodka and fuel and temporarily closing all southbound lanes.
Emergency personnel have extricated the driver of the big rig, but Pilger did not know the driver's condition.
The left two lanes on the southbound side have reopened, but authorities are advising commuters to take alternate routes if possible, as traffic is still slow in the area.
Northbound traffic is not affected, Pilger said.
The California Highway Patrol issued a Sig-alert at 8:07 a.m.