Sept. 16 (UPI) -- Firefighters made substantial progress over the weekend fighting a large wildfire in Northern California that's been burning for nearly two weeks and has charred more than 50,000 acres, fire authorities said.
Officials said the Walker Fire is now 68 percent contained in the Plumas National Forest, northwest of Sacramento. The blaze began Sept. 4 and quickly grew to 17,000 acres. More than 2,000 personnel are assigned to the fire, which has now burned 54,518 acres -- the largest U.S. wildfire of the year so far.
"Firefighters, air resources and equipment will be in all areas of the fire area remaining vigilant and continuing to strengthen and secure the fire perimeter," the U.S. Forest Service said.
The fight became more difficult Sunday with winds up to 40 mph, which sent embers as far as a half-mile away.
"The unburned fuels within the interior of the fire ignited during the strong southwest winds," the U.S. Forest Service said.
The fire has not yet destroyed any structures, officials said.
Thunderstorms forecast for Monday could help firefighters control the flames.
The Murdock Crossing and Stony Ridge areas have been placed under a mandatory evacuation.