It happened before 3:30 am Tuesday.
The California Highway Patrol says the big rig was hauling two empty trailers when the driver lost control and hit a guard rail.
The semi-truck ended up jackknifed.
A large piece of concrete also appeared to fall from the guardrail onto Belmont Avenue.
Westbound traffic on the highway is closed and being moved off at Blackstone Avenue.
Officers believe speed and wet roads from the rain were factors in the crash.