Names have been released in Wednesday´s accident on Tuolumne and Wards Ferry Roads.
Officials say 79-year-old Marjorie Lindsley was at a stop sign on Wards Ferry and then pulled out into the intersection.
She failed to see 16-year-old Jennifer Potter, who was eastbound at the time.
Potter was unable to avoid hitting Lindsley.
The teen suffered minor injuries but Lindsley had to be airlifted to Doctor´s Medical Center in Modesto with severe injuries.
Officers with the California Highway Patrol remind drivers to use extra caution with all the traffic that´s on the roadways and always wear seat belts.
The drivers of both cars in Wednesday wreck were wearing seat belts.