Here we go again.

Fire crews were working feverishly to contain a swiftly moving wildfire near the western border of Yosemite National Park that increased its size 16-fold on Saturday, forcing about 300 homes to be evacuated near the community of Midpines and threatening up to 2,000 residences.

The developments came as officials announced the death of an 18-year-old firefighter who was struck and killed by a falling tree Friday while helping to contain a wildfire in the Shasta-Trinity National Forest about 50 miles west of Redding.

The firefighter, Andrew Palmer, was based at the Olympic National Park in Port Angeles, Wash., and had been sent to California to help battle hundreds of blazes that started after a series of lightning strikes in late June, fire officials said.

Palmer, a National Park Service employee, was killed while working on the Eagle Fire, a 22,131-acre blaze that is part of the Iron Complex. That series of nearby fires is 64 percent contained after scorching 73,859 acres since lightning sparked the blaze on June 21, fire officials said.

The exact circumstances surrounding Palmer's death about 5:45 p.m. Friday are being investigated, U.S. Forest Service spokeswoman Barbara Rebiskie said.

Meanwhile, a fire burning in steep terrain on both sides of the Merced River about 30 miles west of Yosemite Valley exploded Saturday afternoon from 1,000 acres to 16,000 acres, a state fire official said.

That prompted the evacuation of about 300 homes around Midpines, an unincorporated foothills community with a gas station, general store and post office on the approach to Yosemite National Park from Merced along Highway 140, Mariposa County Sheriff Brian Muller said.

The residents of 200 more homes could be ordered to evacuate today, Muller said. The fire threatens about 2,000 homes, said Daniel Berlant, a spokesman for the state Department of Forestry and Fire Protection. Highway 140 remains open.

"This fire moved much faster and has acted much more erratically than anybody anticipated," Muller said. "The fire has created its own weather. ... You had a situation where one minute it was burning south and the next minute it's burning to the east or the north. It was just extremely erratic."

Dry timber and underbrush that haven't burned in decades were creating sections of fire where flames leapt as high as 100 feet, Berlant said.

"Some of these areas haven't seen fire in over 100 years," Berlant said. "There's a lot of vegetation that hasn't burned in a very long time."

The blaze, named the Telegraph Fire, was burning in the Merced River drainage after starting Friday near Telegraph and Sherlock roads, about 6 miles northwest of the main Midpines settlement, officials said.

Investigators have determined it was caused by target shooting, Berlant said.

About 900 firefighters along with helicopters, air tankers, bulldozers and fire engines were trying to counter the fire, which was considered zero percent contained. A record-setting 2,093 wildfires have ravaged California since June 20, feeding on extremely dry vegetation during a time that historically had not been considered high fire season.

"Late July and August, this is when we typically start to see wildfires open up across the state," Berlant said.