With evacuation orders being lifted Friday, investigators worked to determine whether an unusually early and intense outbreak of wildfires in Southern California this week was ignited by something as ordinary as sparks from cars or something as sinister as an arsonist.
State fire officials said the first of at least 10 blazes that broke out between Tuesday and Thursday was found to have been caused by a spark from malfunctioning construction equipment. But it could take months to get to the bottom of the rest of the fires.
"We are not ruling out anything," San Diego County Sheriff Bill Gore said.
All together, the fires burned through more than 10,000 acres in the San Diego area, killing one person and causing more than $20 million in damage. At least eight houses, an 18-unit condominium complex and two businesses were destroyed, and tens of thousands of people were asked to leave their homes.
Six of the fires popped up within hours on Wednesday — raising suspicions that some had been set.
The region has become a tinder box in recent days because of conditions not normally seen until late summer — extremely dry weather, 50 mph Santa Ana winds, and unusually high temperatures in the 90s. On Friday, though, cooler weather aided the 2,600 firefighters, and thousands of people began returning home.
In one of the hardest-hit cities, Carlsbad, investigators finished examining the burn site across the street from a park and focused on interviewing people who called a hotline that was set up to report any suspicious activity.
"Do people have suspicions? Yes," said police Capt. Neil Gallucci, noting there has been no lightning that could explain the blazes. "But can we confirm them? The answer is no."
Police in Escondido, a city north of San Diego, arrested two people, ages 17 and 19, for investigation of arson in connection with two small fires that were extinguished within minutes. But they found no evidence linking the suspects to the 10 bigger wildfires.
The list of possible causes is long.
"Our investigation might be over quickly for some of these fires — say, if we find a piece of metal nearby from a catalytic converter that back-fired," the sheriff said. "But others might not be so easy to determine. We'll be talking to people in the areas to see if they saw anything to see if arson might have had a role."
Investigators will visit each burn site and go down a list, marking what they know and don't know.
Is it near a road? That raises the possibility that the flames were ignited by a hot tailpipe, sparks from a catalytic converter or a discarded cigarette from a motorist. Is there a railroad nearby? Are there any power lines?
Two of the blazes broke out at military bases, where training exercises with live gunfire can spark fires.
Fire investigators will also study the ground for footprints or tire tracks. They will analyze the pattern of the burn marks. And they will talk to anyone in the area who may have seen something.
A 2003 wildfire in Southern California that killed 15 people, destroyed more than 2,000 homes and blackened 300,000 acres in October and November was caused by a lost hunter who set a signal fire.
In the latest outbreak, the first blaze started Tuesday in the upscale San Diego suburb of Rancho Bernardo in a field among swaths of land cleared for new development. It burned through more than 1,500 acres before it was contained the following day.
About an hour after authorities announced the situation was under control, a second blaze erupted at a naval weapons base. Then a tractor-trailer caught fire at a Border Patrol checkpoint. By day's end, eight fires were roaring within a 15-mile radius — torching canyons and racing past homes in beach communities and inland suburbs.
The hardest-hit areas were in the cities of San Marcos, where a college campus shut down and canceled graduation ceremonies, and Carlsbad, home to Legoland California amusement park.
A dozen wildfires popping up in a single day is not unheard of in the drought-stricken state, but it's a phenomenon usually seen during the dog days of summer.
"What makes the San Diego area fires so unique is that we had tinder-dry conditions and Santa Ana winds in the month of May, and that's unprecedented," state fire spokesman Daniel Berlant said.
Spagat reported from Carlsbad, California.
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