SAN MARCOS ( — Firefighters aided by calmer winds made progress Thursday against a series of wildfires burning across San Diego County, and authorities collected clues and solicited the public’s help to determine what caused so many blazes to occur simultaneously.

While some of the nine fires were extinguished and thousands of people were able to return to their homes, the Cocos blaze near San Marcos roared back in the afternoon. Flames raced along scrubby hillsides as massive black plumes filled the skies.

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The roughly 1,000-acre Cocos fire has so far damaged at least three homes and is just five percent contained.

Smoke limited visibility to a few feet at times in the city of 85,000 about 35 miles north of San Diego. On one street, five horses wandered nervously in a paddock as firefighters worked to protect nearby homes and barns.

The Cocos flare-up prompted 18,400 new evacuation notices, in addition to the 20,000 residents evacuated Wednesday. San Diego County Sheriff Bill Gore said it was a “reminder to everybody just how volatile this can be.”

(credit: CBS)

(credit: CBS)

Shelters have been set up at Mission Hills High School and San Marcos Middle School.

In addition to dozens of neighborhoods in San Marcos, mandatory evacuations also remain in place for Escondido residents north and west of West Valley Parkway.

“It’s, honestly, pretty scary. And it’s just so unfortunate that this happened,” San Marcos resident Isaac Vallejo said. “It’s my first year here.”

Firefighters found a badly-burned body Thursday in a transient camp in Carlsbad, but it was unclear if the person had died in the blaze.

A Camp Pendleton Fire Department firefighter received medical treatment for heat exhaustion while fighting a square-mile fire on the Marine base, the first injury from the fires.

There have been no major injuries reported.

Strong, erratic winds are pushing the burning embers miles away, igniting new fires. Crews are putting out hot spots to stop further flare-ups.

Gov. Brown has declared a state of emergency for San Diego County due to nine brush fires burning in the area.

The fires have destroyed at least eight houses, an 18-unit condominium complex and two businesses, and has burned more than 15 square miles, causing more than $20 million in damage so far, according to the Associated Press. Most of the damage was in San Marcos and Carlsbad.

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For a moment, flames were lapping at the back door of California State University San Marcos, which canceled graduation ceremonies because of the danger.

“I’m just worried about everyone’s well-being,” Cal State San Marcos student Christopher Ceja said. “We all, at this university, we all love each other.”

(credit: CBS)

(credit: CBS)

Firefighters who have worked in temperatures sometimes topping 100 degrees this week were expected to get relief on Friday. The forecast called for temperatures to peak around 90 and lighter winds. A bigger cool-down was forecast for the weekend.

While drought conditions and unusually high temperatures made the area ripe for wildfires, there are suspicions that at least some of the blazes were set. Gore said arson is being looked at but so are many other possibilities, such as sparks from vehicles.

Fire and police investigators are working together to determine where how the fires started. Gore encouraged the public to contact and authorities with any information.

Since the fires began Tuesday, 125,000 evacuation notices have been sent. Schools and parks across the county were shut down.

While local authorities congratulated themselves for the cooperative effort among agencies and the bravery shown by firefighters, not everyone was pleased.

Greg Saska stood in front of his charred Carlsbad home Thursday in sandals that showed his soot-covered feet. He said he was not impressed with the fire response.

“I don’t want to complain, but I wish they had just made a little more effort to put the fire out,” Saska said. “The end of the house … was still burning. And they (firefighters) just left. And I’m just kinda going, ‘What would’ve been the big deal to stay here another 10 minutes and put that out totally?’ I just don’t get it.”

In San Marcos, firefighters on the ground and in the air fought to save homes as the flare-up sent flames running up a slope in a heavily vegetated area. The fire was being driven by fuel and topography, said Division Chief Dave Allen of the California Department of Forestry and Fire Protection.

“It’s created its own weather pattern there as it sucks oxygen in,” he said.

Calmer winds allowed aircraft to make a heavy contribution to the firefighting efforts. Four air tankers and 22 military helicopters were being used, in addition to local agency helicopters.

Ten of the military helicopters were being used to battle a blaze that grew to almost 9 1/2 square miles on the Marine Corps’ Camp Pendleton.

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Anyone with information on the fire was urged to call CAL Fire at (562)708-9631.

(TM and © Copyright 2014 CBS Local Media, a division of CBS Radio Inc. and its relevant subsidiaries. CBS RADIO and EYE Logo TM and Copyright 2010 CBS Broadcasting Inc. Used under license. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)