Fairfax resident Mary Jane De Carlo became lost while hiking in Ragle Ranch Regional Park after the sun set and called a friend on her cell phone for help, according to the sheriff's department.
The friend then called the sheriff's department, and deputies responded around 6:30 p.m. with a rescue helicopter.
The light from De Carlo's cell phone guided authorities to her location as they swept the park with night vision technology.
Deputies then escorted De Carlo out of the park. She was reportedly cold and said she didn't know if she could have made it out of the park without help.