The accident occurred shortly after 10 a.m. on Highway 154 west of the lake, fire Engineer Russ Sechler said.
An eastbound Chevy Tahoe driven by Julia Brown, 31, of Lompoc crossed over the center line and slammed into a westbound Dodge Caravan driven by Inocencia Mandujano, 28, of Santa Barbara, according to the California Highway Patrol.
Mandujano had to be extricated from her vehicle, and was airlifted to Santa Barbara Cottage Hospital with critical injuries, Sechler said.
Brown and her 3-year-old child were both were taken by ground ambulance to Cottage.
One was critically hurt, but Sechler said he did not know which one. The other suffered minor injuries.
Highway 154 was shut down for about 40 minutes after the collision.