The blaze was threatening some structures near Irvine Lake and the Santiago Canyon Landfill, according to the Orange County Fire Authority and the Orange County Emergency Operations Center. Three abandoned structures caught fire, OCFA said.
The Orange County Sheriff's Department said deputies evacuated around 10-15 people. No injuries were reported.
Campgrounds near Irvine Lake were evacuated.
The OCFA received a call about the blaze at around 10:45 a.m.
As of 6 p.m., the blaze had charred 180 acres and was 50 percent contained. The forward progress of the fire has been stopped, according to the OCFA.
Santiago Canyon Road was closed down between State Route 241 and Silverado Canyon Road due to the flames. The cause of the blaze was not immediately known.