YREKA, Siskiyou County (CBS SF) – A weather spotter observing wildfire in extreme Northern California witnessed a swirling “ash devil” that resulted from unstable conditions in the area.

Bob Smith snapped pictures of the ash devil, also known as a “fire whirl” as the Grade Fire tore through Siskiyou County near Yreka, more than 300 miles north of San Francisco. The photos were posted on the Facebook Page of the National Weather Service of Medford, Oregon Thursday.

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According to the Weather Service, the ash devil results from strong updrafts from the heat of the fire or the blackened ground, which gives rise to spinning columns of air. Officials said the extreme instability is very dangerous to firefighters.

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According to Cal Fire, the Grade Fire has scorched 710 acres since it broke out Wednesday and has destroyed four residences and four outbuildings. The fire is 65 percent contained as of Friday morning.

Evacuation orders for several hundred people in the area have been lifted, but 150 structures remain threatened.

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The cause of the fire is not known.