The woman, who was not immediately identified, went off the 241 Toll Road in the Santiago Canyon area at about 6:45 a.m., Orange County Fire spokesman Steve Concialdi told KTLA-TV.
About 20 firefighters responded, freeing the woman from the vehicle just after 8 a.m., Concialdi said on Twitter.
"She's very lucky to be alive. I've been in the Highway Patrol about 20 years and this is definitely up there with one of the more amazing things I've seen," said California Highway Patrol Sgt. Chris Johnson.
The car was stopped by a tree in a dry creek bottom about 30 feet off the ground, Concialdi told KTLA. The incident came hours before storms were slated to bring the largest amount of rainfall Southern California has seen in two years.
"If we would have had the rain, it would have been extremely slippery and that car probably would have slipped even further down off the tree and come down," Concialdi said. "She might not be alive today."
The car appeared to be a silver sedan which was seriously damaged and resting northwest of Irvine Lake.
The woman was taken to Western Medical Center in Santa Ana with moderate injuries. Authorities were investigating what caused the car to veer off the roadway.