A destructive wildfire near Yosemite National Park burned out of control through tinder-dry forest on Sunday and had grown into one of California’s biggest blazes of the year, forcing thousands of residents to flee remote mountain communities.

Some 2,000 firefighters battled the Oak Fire, along with aircraft and bulldozers, facing tough conditions that includes steep terrain, sweltering temperatures and low humidity, according to the California Department of Forestry and Fire Protection, or Cal Fire.

“It’s hot out there again today,” Cal Fire spokesperson Natasha Fouts said Sunday. “And the fuel moisture levels are critically low.”

Crews on the ground protected homes as air tankers dropped retardant on 50-foot flames racing along ridgetops east of the tiny community of Jerseydale.

Light winds blew embers ahead into tree branches “and because it’s so dry, it’s easy for the spot fires to get established and that’s what fuels the growth,” Fouts said.

The fire erupted Friday southwest of the park near the town of Midpines in Mariposa County. Officials described “explosive fire behavior” on Saturday as flames made runs through bone-dry vegetation caused by the worst drought in decades.

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