Crews made progress in the firefight Monday night, setting backfires that created a fire break and helped halt the spread of the flames.
The fire first broke out Monday late Monday morning.
Since then, three firefighters were treated for minor injuries and heat exhaustion, and a fourth suffered a minor shoulder injury.
No homes were immediately threatened by the fire.
Orange County Fire Authority Battalion Chief Kris Concepcion says the fire was sparked by a downed power pole on a rugged hillside, 10 miles east of San Juan Capistrano.
A tractor clearing brush in the area knocked down the pole and those power lines then ignited the flames.
CNS contributed to this report.