UPDATE: 1 lane of I-5 closed north of Los Angeles after Castaic wildfire

A fire burning in Castaic Monday afternoon, May 13, 2013.
A fire burning in Castaic Monday afternoon, May 13, 2013.

Crews continue to build containment lines around a 50-acre wildfire started by a burning tractor-trailer north of Los Angeles that forced the closure of one lane of Interstate 5.

Forest Service spokesman Nathan Judy says the blaze sparked in hot weather and tinder-dry vegetation near Castaic Monday is 80 percent contained. Full containment is expected by the end of the day Tuesday. There are no open flames but crews are keeping an eye out for flare-ups.

The fire slowed northbound traffic on I-5 to a crawl and briefly threatened a mobile home park. One lane of the interstate remains closed.

As hot weather and tinder-dry vegetation kept fire crews busy across Southern California, the blaze started in Castaic shortly after 3:30 p.m. Monday and quickly moved into the brush along the freeway, said Los Angeles County Fire Inspector Anthony Akins.

All but two lanes of I-5 were shut down for hours, reducing traffic to a near-standstill for much of the night on the major freeway about 40 miles north of Los Angeles, the California Highway Patrol said.

Soaring temperatures throughout the region, combined with scarce rainfall, combined to create high fire danger.

Elsewhere, firefighters are getting a handle on a 75-acre wildfire north of Fontana, in San Bernardino County, that downed some power lines.

That fire is 45 percent contained. Full containment was expected Tuesday.

No structures were threatened, and there were no injuries.

Even though the area had recent rain, the heat that followed dried the vegetation again and created a fire hazard, said Daniel Berlant of the California Department of Forestry and Fire Protection.

"Hopefully, we don't let the rain fool anybody," he said. "Fire season is still here."

About 20 miles northeast of downtown San Diego, a brush fire near Barona Resort and Casino had consumed about 15 acres in 90-degree heat before firefighters contained it.

This story has been updated.