The fire, which is burning near the Northern California town of Oroville, is threatening 500 homes and another 800 outbuildings.
The declaration will free up additional resources to battle the blaze, which erupted on Tuesday from a campfire that was started outside a designated area.
Three more communities were evacuated, and firefighters struggled to contain the fast-burning flames Wednesday as temperatures surged into triple digits. The vast majority got there by a state highway that was closed for several hours because of the fire. 1,300 structures remain threatened.
"We take our responsibility to assess this new tool during the interim approval process very seriously", said Chief Dave Teter, CAL FIRE's Deputy Director of Fire Protection.
Cal Fire investigators arrested John Ballenger, 29, of Oroville, on suspicion of starting an illegal campfire.
Flames from the Ponderosa Fire burn a home east of Oroville, Calif., on August 29, 2017.
Ballenger is charged with two counts of arson for recklessly starting the fire and was ordered held on a $1 million bond, Ramsey said.
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Months later, a wildfire about 15 miles (24 kilometers) south of the dam destroyed 41 homes in July.
It prompted authorities to issue evacuation orders earlier this week to residents of some 500 homes. Multiple wildfires now burning across the state. The Cherry Fire has been contained at 25 acres.
Thousands of homes have been evacuated and the main travel route to the Burning Man festival closed after other wildfires across the US.
Air quality from wildfire smoke is a problem in Montana and OR, where athletic events from kayaking and half-marathons to high school football games have been postponed in the outdoors-loving state.
In Glacier National Park, smoke from wildfires has led officials to close the historic Lake McDonald Lodge for the season.
Video posted online by media showed the fire burning along the 210 Freeway when it broke out on Friday, with smoke hovering over the roadway as cars passed by flames a few dozen feet away.