The fast-moving Oak Fire in east-central California’s Mariposa County grew more than 2,000 acres overnight, burning an estimated 6,555 acres by Saturday morning after igniting the day before.

Cal Fire said the wildfire still had no containment Saturday. The blaze is threatening an estimated 2,000 structures, destroyed 10 and damaged five, Cal Fire reported.

“Fire activity is extreme with frequent runs, spot fires and group torching,” Cal Fire officials said of the Oak Fire. “Emergency personnel are working to safely evacuate people and are actively engaged in protecting structures. Explosive fire behavior is challenging firefighters.”

The fire started about 2:10 p.m. Friday in rural Midpines, about a 20-minute drive from Mariposa and an hour from Yosemite National Park. The cause of the fire remains under investigation.

It’s the third wildfire to erupt this month in the Yosemite area. Wawona Road (Highway 41) from Yosemite’s south entrance to Yosemite Valley was scheduled to reopen at 6 a.m. Saturday after closing due to the Washburn Fire. Yosemite officials said the Mariposa Grove of Giant Sequoias and Wawona remain closed.

The Washburn Fire has burned 4,856 acres and is 79 percent contained, according to Yosemite National Park. And the Agua Fire burned 421 acres and is completely contained, according to Cal Fire.
Full containment of the Oak Fire isn’t expected for at least a week. Around 400 personnel were assigned to the Oak Fire as of Saturday morning, including 11 hand crews, four helicopters, 45 fire engines, four bulldozers, and four water tender trucks.

The fire had grown so big in such a short amount of time that a pyrocumulus cloud formed Friday afternoon and could be seen more than 120 miles away in the Bay Area.

Crystal Kolden, a pyrogeographer and a professor at UC Merced, said the pyrocumulus cloud was a result of smoke rising “until it hits the upper-level winds, stalls, and then suddenly punches through.”

The smoke cloud from the Oak Fire became so big, in fact, it could been seen from outer space via a camera on the NASA international space station.

Kolden, who studies wildfire, added that the Oak Fire was expanding due to three primary factors: fuel load, heat and the very dry air due to a 108-degree day.

The professor said the area hasn’t burned since 1924.