The crash was reported at about 1:45 p.m. on westbound Highway 80 near Cherry Glen Road, CHP Officer Ron Simmons said.
According to preliminary information, a tree appeared to have fallen into the roadway, partially obscuring the far right lane, according to the CHP.
A vehicle driving in that lane crashed into the tree, killing one occupant, Simmons said.
The Solano County coroner responded to the scene.
Portions of Highway 80 were blocked for nearly two hours, but the roadway was cleared by 3:30 p.m., the CHP said.