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David Middlecamp, The Tribune (of San Luis Obispo) via AP
Area residents observe the progress of the Cuesta Fire as it burns downhill Monday, Aug. 17, 2015, on the Santa Lucia Range east of Santa Margarita, Calif., as seen from Highway 58.

FRESNO, Calif. (AP) — A blaze burning for nearly three weeks on the western slope of the Sierra Nevada surged in size in a recreation area outside Kings Canyon National Park where more than 2,500 campers, hikers, employees and residents have been evacuated.

The blaze crossed Highway 180 and a river prompting the evacuation of the area near Hume Lake, a reservoir that is one of Sequoia National Forest's most visited destinations and the site of a Christian youth summer camp.

Sparked by lightning July 31, the Fresno County blaze tore through timber, brush and tall grass in the Sierra National Forest, growing to nearly 48 square miles. It was just 3 percent contained Wednesday.

East of San Francisco, a fast-moving grass fire scorched nearly 4 square miles of dry brush near Livermore. At least one structure was destroyed, officials said, but it was not clear if it was an outbuilding or a residence. The Carnegie State Vehicular Recreation Area was evacuated after the flames were reported Wednesday.

In San Luis Obispo County, evacuation orders were canceled Wednesday afternoon for about 800 people driven from their homes near the small town of Santa Margarita earlier in the week.

At more than 5 square miles, the blaze burning in steep terrain was 20 percent contained, said Bennett Milloy, spokesman for the California Department of Forestry and Fire Protection. Full containment is expected to take another week.

There are 16 wildfires burning in California with more than 10,000 firefighters on the front lines. While a new wildfire ignited Tuesday in Humboldt County, firefighters contained three other wildfires that had been burning. The Humboldt County fire, northeast of Shelter Cove, has burned about 50 acres and was 5 percent contained Wednesday.

Firefighters were dealing with abnormally high temperatures for the season, drought-stressed fuels that haven't burned in 30 years, steep terrain and the danger of oak tree mortality, Milloy said.

"These oaks become so starved for moisture," he said. "We heard them falling all night last night."

More than 440 California National Guard soldiers joined the firefighters this week, and thousands more were being trained, according to Cal Fire's Mike Mohler.

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Cal Fire spokesman Daniel Berlant said with temperatures returning to a more seasonable level, firefighters are hoping to continue making progress on the wildfires burning statewide.

Authorities in Mono County said two men posing as reporters tried to gain access to a wildfire burning north of Walker Lake. Aaron Browne, 44, and Payton Ware, 33, were dressed in new firefighter-type gear and presented fake media credentials, the Mono County Sheriff's Office.

A check showed Browne is a convicted felon and he was arrested after officials found a case of pepper spray in his pickup truck. Ware was released at the scene, the office said.