SAN FRANCSICO (CBS SF/CNN) — As the Creek Fire bore down on hundreds of trapped campers near Mammoth Pool, the flames were also being fanned by a firenado with winds topping 100 mph, according to federal forecasters.

While the fire — burning in the drought and bark beetle damaged timberlands of the Sierra north of Fresno — stood at 291,426 acres and was 36 percent contained on Friday morning. The blaze has destroyed 502 homes and 18 commercial structures in the rural communities.

“It’s burning real well on north side just south of the San Joaquin River,” said Cal Fire Capt. Don Watt at Thursday night’s update. “We’ve seen a lot of action up there over the last several days. It’s burning actively in the low humidity and large fuels. In a lot of other areas, the fire is starting to hit rock sprees and slow down a little bit.”

There have been no fatalities reported, but had it not been for the bravery of National Guard helicopter pilots, that number would have been much higher, particularly at Mammoth Pool.

Black Hawk and Chinook helicopter crews braved heavy smoke, high winds and nearby flames to rescue more than 200 trapped people on Sept. 5th and continued through the overnight hours. At least two people were severely injured and 10 more suffered moderate injuries.

Officials said the intense heat of the fire, fueled by thousands of dead trees, created it own weather system and sent a pyrocumulus cloud soaring thousands of feet into the sky.

Federal forecasters said one firenado was rated an EF-2, with winds up to 125 miles per hour. The other had winds of up to 100 miles per hour and was rated an EF-1. Both took place on Sept. 5th.

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  • The firenados wreaked havoc across the rugged area, the result of “unprecedented fire behavior,” government forecasters said Thursday.

    Fire tornadoes are created when the rising heat from a fire pulls in smoke, fire and dirt, creating a rotation vortex above the blaze, according to CNN meteorologist Haley Brink.

    “To have even one tornado within a fire is rare,” CNN meteorologist Taylor Ward said. “Fires can lead to fire whirls — kind of like a dust devil — due to differential heating, but to get a tornado with winds of over 100 mph is quite unusual.”

    The tornadoes uprooted pine trees, snapping even several 2-foot diameter trees and stripping bark from their trunks, a storm survey report said.

    The historic wildfires California is experiencing this year have generated intense heat, causing the vortices to form, meteorologist Jerald Meadows at the National Weather Service office in Hanford, California, told CNN on Thursday.

    While Meadows can’t say for certain the state is seeing more firenados than in the past, he said we will learn more as the technology has improved to track and monitor their formation.

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