The CHP says the overturned big rig was loaded with metal beams from the old Bay Bridge, which is slowly being dismantled.
The beams are huge, so the cleanup is going to involve getting a crane to reload the truck.
The CHP says this could take hours.
The accident happened just after 9 a.m. on Wednesday morning.
The CHP says that speed may have been a factor, but they do not think it is rain-related. Nobody was injured.