Calmer winds allowed firefighters to make progress on nine fires burning in the San Diego area as one of the most serious blazes suddenly roared Thursday afternoon burning close to homes, triggering thousands of new evacuation orders.

Growing flames raced along scrubby hillsides near the city of San Marcos as massive black plumes filled the afternoon skies after a half-day lull in winds that had allowed firefighters to gain ground against flames that have scorched thousands of acres this week.

Ash laden smoke limited visibility to a few feet at times in the inland suburban community. On one semi-rural street, five horses wandered nervously in a paddock as firefighters worked to protect nearby homes and barns.

Sheriff Bill Gore said the flare-up prompted more than 13,000 new evacuation notices in the San Marcos area and served as a "reminder to everybody just how volatile this can be." The new evacuations were in addition to more than 20,000 orders issued Wednesday. About 85,000 people live in San Marcos.

Since the first blaze erupted Tuesday during a heat wave, officials have repeatedly predicted the worst was over only to be confronted by a new challenge amid the hot, dry and windy conditions.

The fires have destroyed eight houses, an 18-unit condominium complex and two businesses and burned more than 15 square miles (39 square kilometers), causing more than $20 million in damage so far.

Firefighters found a badly burned body in a transient camp in Carlsbad, a north San Diego suburb that was one of the hardest hit areas by this week's fires. The city of Carlsbad said it had no information about the person who died — apparently the first fatality of the fires.

The flare-up in San Marcos ran up a slope in a heavily vegetated area but with no wind on it. 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 told a news conference.

State fire Capt. Kendal Bortisser said the fire was running east along hillsides behind California State University San Marcos.

The fire, which broke out Wednesday, forced the evacuation of the university campus where nearly 10,000 students were in the middle of final exams. Graduation ceremonies were canceled.

Investigators were trying to determine the causes of the various fires.

Asked about the possibility of arson, the sheriff said he wouldn't prejudge the investigations. He noted that sparks from vehicles can easily ignite brush in such dry conditions.

Emergency officials said a significant number of firefighting aircraft had become available, including four air tankers and 22 military helicopters, in addition to local agency helicopters.

Since the fires began, 125,000 evacuation notices have been sent, officials said. Schools also have been shut down and the Legoland amusement park had to close Wednesday. It reopened Thursday.