Shortly before 5 p.m., it appeared that firefighters had it well under control.
At 5:30, authorities said the fire was 50-percent contained. Full containment was expected Wednesday night, and full control was expected by Thursday morning.
About 200 firefighters were on the scene, according to fire officials. Two air tankers and three helicopters were called in to drop fire retardant and water on the fast-moving brusher.
No injuries were reported, and no structures were threatened.
"Initially, on my way here, I could see a large plume buildup of smoke. What I heard on the radio and from the incident commander was that the fire was moving uphill and was moving out pretty fast," said Orange County Fire Authority Captain Greg McKeown.
"The homes right now are a concern," said McKeown. "We have units up in those homes patrolling and staging up there, should the fire move in that direction. There are no evacuations called at this point in time."
The fire was approximately a mile to a mile and a half from the nearest houses.
Crews from the Riverside County and Corona fire departments, as well as the Orange County Fire Authority, worked to contain the blaze.
Temperatures were in the upper 70s with 17 mph winds and 40 percent relative humidity. The wind was described as "swirling" by firefighters.
The Associated Press contributed to this report.