HARRISBURG -- Forty Pennsylvania firefighters ran into triple-digit temperatures yesterday as they began their first full day combating wildfires that are scorching northern California.

Two 20-person crews, including four firefighters from Western Pennsylvania, left Sunday from Harrisburg International Airport on a U.S. Forest Service-chartered jet. They arrived Monday and joined hundreds of other firefighters in trying to control the blaze that has burned since June 20, said John Miller, chief of Pennsylvania's forest fire protection division.

"With the amount of fire activity in California right now, it's very important" to get help from other states, said James Stone, a California Forest Service spokesman. "Those boys from Pennsylvania are a significant portion of that."

Of the 40 Pennsylvanians who've gone to the West Coast, one is from Somerset County and three from Westmoreland County, said Brian Vinski, a supervisor in Pennsylvania's fourth forest district in Ligonier.

Officials declined to provide the firefighters' names, citing privacy reasons.

The crews are working in the 10,000-acre Ukonom Complex, a series of wildfires started by lightning in rural Humboldt County, on the north coast of California near the Oregon line.

The Pennsylvania crews are part of roughly 330 firefighters working there.

"Not only are we assisting folks in other states," said Mr. Miller, "but our capacity [in Pennsylvania] will increase because of the level of experience they will bring back."

Some firefighters are state employees, who will be paid their usual rate of pay. Others are volunteers paid $12 an hour by the U.S. Forest Service, Mr. Miller said.

As of yesterday, the Ukonom Complex was just 12 percent contained and will likely burn through October. Typical shifts last between 12 and 15 hours and run for two weeks before replacements are called in, Mr. Stone said.

"With 14 days of 12-, 13-, 14-hour work days in triple-digit heat," Mr. Stone said, "you can only work them so long."