Gerd Dunker, 48, of Sonoma, was traveling west toward Petaluma east of Adobe Road when he made an unsafe turning movement and collided head-on with an eastbound 18-wheel tractor-trailer around 9:45 a.m., the CHP said.
Dunker and his passenger, Angela Franck, 42, of Sonoma, suffered severe injuries and were taken to Santa Rosa Memorial Hospital.
Both vehicles sustained major front-end damage, CHP Officer Jaret Paulson said.
The collision pushed the Ford into a Jeep Liberty that was traveling behind the Ford, Paulson said.
The Jeep's driver, Yesenia Chavira, 27, of Rohnert Park, was not injured.
The driver of the big-rig, Clemente Garcia, 41, of Quebec, Canada, was also uninjured, CHP Officer A. Paulson said Tuesday morning.