The fire was reported about 4 p.m. Saturday at Gilman Springs Road at the 60 Freeway. The blaze consumed 150 acres by 5:30 p.m. By Saturday night, the fire was 35 percent contained.
No structures were being threatened. The fire was moving east, away from nearby communities.
The California Highway Patrol closed the 60 Freeway from Theodore Street to Interstate 10. The eastbound lanes were later opened, but the westbound lanes remained shuttered.
Officials said 50 to 60 motorists were stranded, but were safely evacuated.
Nearly 200 firefighters were at the scene, Riverside County Fire Department spokeswoman Cheri Patterson said.
The cause of the fire is under investigation.