An army of nearly 2,200 fire-fighting personnel battling the so-called Bootleg fire, about 250 miles (400 km) south of Portland, increased their containment lines to 25% of its perimeter, up from 22% a day earlier, Oregon Department of Forestry spokesman Marcus Kauffman said.
"We are fighting the fire aggressively, and there are active efforts to build a containment line, both direct and indirect, wherever it is safe to do so," Kauffman said.
Extreme fire behavior on Sunday forced some ground crews to fall back to "safety zones" for a ninth straight day and regroup as they "looked for opportunities to re-engage," incident commander Joe Hessel wrote in his daily report. "This fire is a real challenge, and we are looking at sustained battle for the foreseeable future."
Since erupting on July 6, the blaze has charred nearly 304,000 acres (123,020 hectares) in and around the Fremont-Winema National Forest, equal to nearly half the land mass of Rhode Island. Only three other Oregon wildfires over the past century have consumed more acreage, according to state forestry figures.
The Bootleg also stood as the biggest, by far, of 80 major active wildfires that have collectively burned nearly 1.2 million acres in 13 states, according to the National Interagency Fire Center in Boise, Idaho. More than 19,600 firefighters and support personnel are confronting those flames.
The spate of conflagrations, marking a heavier-than-normal start of the Western wildfire season, has coincided with record-shattering heat that has baked much of the region in recent weeks and is blamed for hundreds of deaths.
Scientists have said the growing frequency and intensity of wildfires are largely attributable to prolonged drought and increasing bouts of excessive heat that are symptomatic of climate change. (Graphic on megafires)
Since starting nearly two weeks ago, the Bootleg fire has thrived from a combustible triad of weather conditions - gusty winds, high temperatures and low humidity - that are expected to persist in the days ahead. Forecasts on Monday added a chance of thunderstorms to the mix.
"Thunderstorms often just come with dry lightning and wind and don't necessarily produce any precipitation," Kauffman said.
Two evacuation centers, one at the Klamath Falls fairgrounds and one at a middle school in Lakeview, have been set up for residents displaced by the fire, which has destroyed 67 homes and was threatening 2,460 more. More than 100 outbuildings and other structures also have been lost. An estimated 2,100 people were under evacuation orders on Monday and many more were on standby alert to be ready to flee at a moment's notice.
The cause of the Bootleg was under investigation.
In California, PG&E Corp (PCG.N), the state's largest power company, said some of its equipment may have been involved in sparking the Dixie fire last Tuesday in a remote area about 85 miles (140 km) north of Sacramento.
That wildfire has burned over 30,000 acres (12,140 hectares) as more than 1,900 fire-fighting personnel carved containment lines around 15% of its periphery, according to the California Department of Forestry and Fire Protection.
The Dixie fire has prompted some evacuation orders for Plumas and Butte counties, CalFire reported.
In an incident report to state regulators on Sunday that PG&E described as preliminary, the company said one of its workers last Tuesday found blown fuses on a utility pole and spotted a fire near the base of a tree that was leaning into a conductor. The worker reported the fire, it said.
Thirteen months ago, the company pleaded guilty to 84 counts of involuntary manslaughter stemming from a devastating 2018 wildfire touched off by wind-damaged power lines that destroyed much of the nearby town of Paradise. Reporting by David Ryder in Bly, Oregon; Writing by Peter Szekely and Steve Gorman; Editing by Lisa Shumaker and Karishma Singh