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(CNN) -- Blistering hot temperatures will blast the normally tepid Pacific Northwest again Thursday as dozens of wildfires burn across large sections of the western United States.
The mercury is expected to soar near triple digits in Portland, Oregon, with Seattle forecast to reach the lower 90s, the National Weather Service said. The coastal region is roasting under an excessive heat warning.
At least 70 large fires were burning across 13 states west of the Mississippi River, according to the National Interagency Coordination Center. California had the most with 13, followed by Nevada with 12 and Idaho with 10, the center said.
The Marines joined the fight on Wednesday, with helicopter units from California joining U.S. Air Force Reserve and Air National Guard units from Colorado, Wyoming, North Carolina and California in fighting the fires by air. The Marine units will help fight fires around San Diego.
In California alone, 8,000 firefighters were fighting a dozen fires, the state Department of Forestry and Fire Protection said Wednesday. The state issued a burn ban, saying only some campfires are allowed.
Conditions could worsen in some places over the next few days. The National Weather Service said a weather pattern developing in parts of Oregon could produce conditions favorable to "explosive fire growth."
In central Washington state, the wind-whipped Taylor Bridge Fire had scorched some 22,600 acres and destroyed at least 60 homes, fire officials said.
One of those structures was the home of Elaine Burt, who unsuccessfully tried to get past firefighters to save her dogs and other animals at her home, according to CNN affiliate KING-TV..
After the initial heartbreak of being told all of them were gone, she learned Wednesday that Hannah, one of her dogs, and six of her pigs had survived.
"Oh Mama ... hi mama," Burt said when she saw her sow at the Kittitas County Fairgrounds. "One, two, three, four, five, yup, that's all her little babies."
Washington Gov. Chris Gregoire declared Kittitas and Yakima counties to be in states of emergency, according to a written statement from her office. The Washington National Guard will provide air support to the Department of Natural Resources, which is in charge of statewide firefighting efforts.
Authorities have already evacuated around 900 people near the Taylor Bridge Fire, the governor's office said. No injuries were reported.
More than 900 firefighters were battling the fire near Cle Elum, Washington, said Rex Reed, the incident commander. The Incident Alert System showed the blaze was 25% contained early Thursday
The weather was "cooperating" Wednesday, he said, referring to calmer winds, but firefighters have their work cut out for them the rest of the week. Hot and dry conditions are expected.
"Unless Mother Nature helps us out here, we're going to be fighting this a while," Joe Seemiller, a captain with Kittitas County Fire and Rescue, told CNN affiliate KOMO-TV.
Elsewhere, more evacuations were under consideration near Featherville, Idaho, where more than 800 firefighters were trying to get a hand on the sprawling Trinity Ridge fire.
The fire grew significantly since Tuesday, burning more than 68,000 acres and forcing authorities to call an emergency meeting of residents of Featherville and nearby Pine to discuss possible evacuations.
Near the border between Oregon and California, crews were battling an aggressive southern run by the Barry Point Fire, which has torched some 59,000 acres of land in the two states, according to the incident command team's website.
With temperatures above 90 degrees, low humidity and wind gusts nearing 20 mph, the lightning-sparked fire has a high potential for further growth, the interagency center said, forcing the evacuation of homes in California, 15 miles south of the state border.
More than 800 firefighters and support personnel were working in Oregon and Nevada to corral the 436,600-acre Holloway Fire, the largest of the Western wildfires. It was ignited by a lightning strike on August 5.
Incident commanders said Wednesday that they hope to have the Nevada portion of the fire out on Wednesday.
In Northern California, the Rush Fire had torched 101,000 acres since Sunday, the National Interagency Coordination Center reported.
Meteorologists predict the dry heat will last into next week, not good news for firefighters. Any thunderstorms that pop up could present more bad news than good, since lightning strikes could spark more flames.
As of Wednesday, wildfires have burned through 6.47 million acres this year, surpassing the 6.36 million acres burned by this date last year, according to the National Interagency Fire Center.
The total acreage burned this year is about 3.4 million acres short of the record set in 2006, when 1,801 fires burned a total of 9.87 million acres, according to center statistics.
CNN's Ed Payne, Dan Simon, Moni Basu and John Fricke contributed to this report.