It happened around 9:40 p.m. on southbound Highway 99 north of Childs Avenue.
Officials say the semi-truck collided with a Cadillac and drove off the highway. The truck hit Crystal Geer, 38, and an unidentified man while they were sleeping at the encampment.
The man died at the scene, and Greer was treated for minor injuries.
Both drivers were not injured, and neither is facing charges at this time.
The cause of the crash is still under investigation.