California’s largest wildfire merged with a smaller blaze and destroyed homes in remote areas with limited access for firefighters, as numerous other fires gained strength and threatened property across the U.S. West.

The massive Dixie Fire, which started July 14, had already leveled over a dozen houses and other structures when it combined with the Fly Fire and tore through the tiny Northern California community of Indian Falls after dark Saturday.

An updated damage estimate was not available Sunday, though fire officials said the blaze had charred nearly 298 square miles acres (772 square kilometers) of timber and brush in Plumas and Butte counties. It was 21% contained.

Firefighters carrying hand tools were forced to hike through rugged terrain where engines can’t go, said Rick Carhart, spokesman for the California Department of Forestry and Fire Protection.

“It has been burning in extremely steep canyons, some places where it is almost impossible for human beings to set foot on the ground to get in there,” he said. “It’s going to be a long haul.”

Still, crews made progress Saturday by proactively setting fires to rob the main blaze of fuels, Carhart said.

The fire prompted evacuation orders in several small mountain communities and along the west shore of Lake Almanor, a popular resort area.

Firefighters also reported progress against the nation’s largest wildfire, the Bootleg Fire in southern Oregon, containing 46% of the blaze that had consumed nearly 640 square miles (1,657 square kilometers).

More than 2,200 firefighters battled the blaze, focusing Sunday on constructing containment lines at the north and eastern edges in dense timber. Crews could get a break from rain and higher humidity predicted for this week, said Marcus Kauffman, spokesman for the Oregon Department of Forestry.

The lightning-caused fire has burned 67 homes, mainly cabins, and at least 2,000 houses were under evacuation orders.

Oregon Gov. Kate Brown told CNN’s “State of the Union” that it’s imperative federal and state authorities invest in mitigation such as tree thinning and preventive burns to limit the number of similar massive blazes. But she conceded that “the harsh reality is that we’re going to see more of these wildfires.”

“They’re hotter, they’re more fierce, and obviously much more challenging to tackle. And they are a sign of the changing climate impacts,” Brown said Sunday.

In California, Gov. Gavin Newsom declared a state of emergency for four northern counties because of wildfires that he said were causing “conditions of extreme peril to the safety of persons and property.” The proclamation opened the way for more state support.

Such conditions are often from a combination of unusual random, short-term and natural weather patterns heightened by long-term, human-caused climate change. Global warming has made the West much warmer and drier in the past 30 years.

In southwest Montana, officials were focusing on structure protection for three area fires amid weather forecasts of rising temperatures, low humidity and westerly winds this week, factors that could produce explosive growth.

About 475 firefighters were working the Alder Creek, Trail Creek and Christensen fires. In particular, crews were trying to protect about 200 homes and cabins and prevent the 44-square-mile (144-square-kilometer) Trail Creek blaze from reaching the Big Hole National Battlefield in Beaverhead County, fire spokesman Jason Nedlo said. The battlefield site, operated by the National Park Service, has been closed because of the fire threat.

Elsewhere in California, the 104-square-mile (269-square-kilometer) Tamarack fire south of Lake Tahoe continued to burn through timber and chaparral and threatened communities on both sides of the California-Nevada state line. The fire, sparked by lightning July 4 in Alpine County, has destroyed at least 10 buildings. It was 27% contained Sunday.

Heavy smoke from that blaze and the Dixie Fire lowered visibility and may at times ground aircraft providing support for fire crews. The air quality south of Lake Tahoe and across the state line into Nevada deteriorated to very unhealthy levels.

In north-central Washington, firefighters battled two blazes in Okanogan County that threatened hundreds of homes and again caused hazardous air quality conditions Saturday. And in northern Idaho, east of Spokane, Washington, a small fire near the Silverwood Theme Park prompted evacuations Friday evening at the park and in the surrounding area. The theme park was back open Saturday with the fire half contained.

Although hot weather with afternoon winds posed a continued threat of spreading blazes, weekend forecasts also called for a chance of scattered thunderstorms in California, Utah, Nevada, Arizona and other states. However, forecasters said some could be dry thunderstorms that produce little rain but a lot of lightning, which can spark new blazes.

More than 85 large wildfires were burning around the country, most of them in Western states. They had burned over 1.4 million acres (2,135 square miles, or more than 553,000 hectares).

(AP)