The cause of the fire was unknown, but officials said they were looking into campers who were in the area. There were no homes threatened.
The fire was one of several blazes that broke out in California as temperatures soared on Saturday.
The fire is in an area with hard access near the 5 Freeway and Ridge Route Road, LACFD Capt. Ron Singleton told City News Service. The National Weather Service says the mercury hit 105 degrees in Lancaster, about 30 miles southwest of the lake.
A small grass fire led to the temporary closure of State Route 13 in Oakland.
Several wildfires broke out in California as temperatures soar across the state.
Around 2:49 p.m., the blaze moved from Los Angeles County Fire territory into the Angeles National Forest.
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The fire near Castaic Lake.
A firefighter was transported for heat exhaustion on Sunday but was released and back on the fire line today, Judy added.
The wildfire, which is burning the peninsula northwest of upper Castaic Lake, was first reported around 2 p.m. Saturday.
Los Angeles County Firefighters are responding to a brush fire that has grown to 500 acres near Castaic Lake and reported to be at zero percent containment.
Smoke has lingered over the lake area since the fire started Saturday afternoon.
In Riverside County over the weekend, firefighters tackled a 10-acre brush fire near Beaumont, a 40-acre fire near Moreno Valley and a 20-acre blaze just north of Lake Elsinore. He says crews were able to clear brush surrounding the fire to stop its spread and that it appeared they had a handle on it.