WATCH: Firenado Over California Wildfires

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SAN MARCOS, California (CBS) -- San Diego County Sheriff Bill Gore says arson will be among the many possibilities investigators will look at in trying to determine what caused nine fires to break out during a two-day heat wave.

Winds did not reoccur in San Diego County wildfire areas Thursday morning. That could be giving firefighters a window of opportunity to make gains against flames that have scorched thousands of acres and destroyed homes.

A significant number of firefighting aircraft are now available, including 22 military helicopters. Twelve of those are available to the county, where the biggest concern is a blaze at San Marcos. That fire is now 800 acres and is just five percent contained. Thousands of people remain evacuated.

Ten of the other helicopters are being used to battle a six thousand acre fire on the Marine Corps' Camp Pendleton.

Fires began erupting Tuesday amid high heat and gusty Santa Ana winds.

Gore said Thursday that it could take months to find the causes of the blazes concentrated in the northwestern area of the county, from the coast to areas 10 to 15 miles inland.

The fires have caused more than 22 million dollars in damage so far.

Posted by: Nick Viviani