At least 25 acres have burned. The fire is 20 percent contained.
Officials said one firefighter has been injured after a fall. He was taken to a local hospital in unknown condition.
More than 100 firefighters are battling the blaze, which is burning in very steep terrain.
The area is remote, and no homes or structures are in danger for now. However, it has not burned there in 15 or 20 years, and the brush is very high. Luckily, there is not a lot of wind.
A SigAlert for Ortega Highway at Mile Marker 14 was issued about 12:30 a.m., according to the California Highway Patrol. The 74 was also shut down in both directions from Grand Avenue in Lake Elsinore through the Riverside County line, a CHP dispatcher said.
City News Service contributed to this story.