(TNS) — With high temperatures and steep, rugged terrain hampering firefighters, a deadly wildfire along the Merced River near Yosemite National Park quadrupled in size overnight and pushed closer to the park Sunday.

The Ferguson fire in Mariposa County had burned through 4,310 acres and was just 2 percent contained Sunday evening, fire officials said. Some 500 firefighters were working the blaze on the ground with support from aircraft.

No structures had burned but 108 were threatened as firefighters worked to protect structures along Highway 140 and prevent the blaze from crossing Ferguson Ridge.

"It is a very active fire, and since we're in a very warm trend, with afternoon temperatures in the triple digits, fire activity is expected to be on the high side," said Alex Olow, a spokesman for the U.S. Forest Service.

The cause of the fire has not been determined.

The fire, which started Friday in the Merced River Canyon and took the life of a firefighter Saturday, caused Pacific Gas and Electric (PG&E) to temporarily shut off power in the area and closed one of the main routes into the national park at the peak of the tourist season.

California Department of Forestry and Fire Protection bulldozer operator Braden Varney, 36, of Mariposa, died when his bulldozer rolled over as he built a firebreak, a Cal Fire spokesman said.

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