Boy started blaze, L.A. County says

A fire that charred more than 38,000 acres and destroyed 21 homes in northern Los Angeles County last week was sparked by a boy playing with matches, sheriff’s officials said Tuesday.

The disclosure about the Buckweed fire, initially blamed on downed power lines, came as firefighters continued to push forward in containing the region’s blazes and as health officials announced that strenuous outdoor exercise was no longer hazardous in most of Southern California. Authorities in all seven counties struck by the fires said air quality had improved significantly.

L.A. County Sheriff’s Department arson investigators did not name the boy believed responsible for the Buckweed fire. Nor did they give his age or the community where he and his family live.

“We have identified a juvenile boy as the person who started the fire,” said Steve Whitmore, a department spokesman. “Arson investigators interviewed the young man, and he acknowledged he had been playing with matches and accidentally started a fire.”

The boy was released to the custody of his parents. The case has been turned over to the Los Angeles County district attorney’s office. The only other information Whitmore provided was that investigators concluded the fire was sparked by an individual the day after it began but that it took more time to link the blaze to the boy.

The fire broke out the afternoon of Oct. 21 in the 11700 block of West Mint Canyon Road in Agua Dulce, an unincorporated area northeast of Santa Clarita in northern Los Angeles County. Fanned by powerful Santa Ana winds, the fire roared south, eventually threatening homes in numerous subdivisions in the Santa Clarita area.

At its height, the blaze forced more than 15,000 people from their homes and was battled by 1,200 firefighters. It was contained Oct. 24.

The improving air quality from progress against the region’s fires prompted health officials to declare that the only Southern Californians who should still avoid outdoor activity were those in eastern areas of Orange and San Diego counties, as well as those with preexisting health problems.

“There are still some areas out near the fires that we continue to advise people that if they’re in the smoke to avoid physical activity,” said Bill Brick, senior meteorologist with the San Diego Air Pollution Control District.

Meanwhile, firefighters battling the region’s remaining blazes said the flames that have plagued Southern California since Oct. 20 would be contained by the end of the week.

In San Diego County, crews were on the verge Tuesday of fully containing the area’s two largest blazes. The Witch fire, which has burned 197,990 acres, was 97% contained. The Harris fire was 90% contained after burning 90,440 acres along the U.S.-Mexico border.

Firefighters in northern San Diego County were hurrying to extinguish the Poomacha fire ahead of the forecast arrival this weekend of more Santa Ana winds. Foggy nights and moister air have helped crews achieve 70% containment. But the firefighters have had to change tactics because the blaze has reached the Agua Tibia Wilderness, an environmentally sensitive area where restrictions prohibit the use of fire engines and bulldozers, Sawyer said.

In San Diego County, 26,000 more residents signed up for a reverse 911 system that automatically calls them if an evacuation is ordered. Preliminary numbers from the San Diego Institute for Policy Research have put the cost of the county’s fires at $2 billion.

Lower temperatures and mild onshore winds have also helped firefighters restrain the Santiago fire burning through Orange County’s back country. The fire, which has scorched 28,445 acres and destroyed at least 15 homes, is 80% contained, and fire authorities are predicting full containment by Sunday.

“The weather is cooperating very well at the moment,” said Capt. Ian MacDonald, a spokesman for the multi-agency team battling the blaze. “Our concentration right now is to complete the [fire] line and to make sure that the fire is not burning in an area where mild Santa Ana winds would intensify it and allow the fire to enter” a populated area.

The fire is moving north and east, burning thick brush in the Cleveland National Forest and threatening about 200 homes in Silverado Canyon.

Roughly 2,000 firefighters are battling the blaze; six air tankers and 12 helicopters are dropping retardant. Hand crews and bulldozers, which built five miles of fire line Monday, were working on the final mile Tuesday.

“It’s extremely rugged terrain,” MacDonald said.

In San Bernardino County, Running Springs residents whose dwellings were destroyed in the Slide fire will be allowed to return to their home sites today to recover belongings, but only between 9 a.m. and 5 p.m. They must also obtain a resident pass beforehand at Rim of the World High School. All other residents may return home at 6 a.m. Thursday, authorities said. There has been no word yet on when residents of Green Valley Lake can return home.

According to officials, the Slide fire, which has scorched 12,759 acres and destroyed 272 structures, is 97% contained. The Grass Valley fire, which destroyed 178 structures, is fully contained, officials reported.

andrew.blankstein @latimes.com

jp.renaud@latimes.com

Times staff writers Seema Mehta, Maeve Reston and Tony Perry contributed to this report.