It was little more than a grave of scorched remains.

Appliances burned beyond recognition, a charred bathtub, twists of metal pipe. Slabs of concrete that once served as walls stood next to a chimney of blackened stone.

Signs of a caring owner — a filled birdbath, potted plants — were suddenly stark symbols of the past, before the Idyllwild home had been consumed by the Cranston fire.

The massive blaze that has sent thousands fleeing as it continues to rage through the San Jacinto Mountains is believed to have been sparked Wednesday by an arsonist, a troubling detail in a battle that has enlisted nearly 700 firefighters and threatened hundreds of homes.

“It’s the scariest feeling you can have because you’re helpless,” said resident Tamara Friemoth, 56, about the moment she watched the fire curl around the mountains in front of the gas station and auto shop she owns with her husband.

Friemoth has lived in the area for four decades and although she ran home to grab clothes and family heirlooms, she kept her business open for firefighters seeking drinks and snacks.

By Thursday afternoon, the fire was 7,500 acres and 5% contained, easily spotted by the billowy plumes of smoke expanding into the sky.

A dusting of crimson retardant atop a ridge marked where the flames had retreated from Idyllwild, an enclave of artists and musicians and a tourist draw. But officials worried the triple-digit weather coupled with a shift in wind could build momentum and undo any progress, even sending the blaze back on top of firefighters and into the beloved town.

Chief Patrick Reitz of the Idyllwild Fire Protection District said his biggest concern was whether the fire might push past a fire line or fuel break.

Over the last several years, staff from local, state and federal agencies have actively worked to build and maintain fuel breaks in the area. Those, mixed with an aggressive air assault team and firefighters on the ground, have helped slow down the Cranston fire and save most of Idyllwild, where five structures were destroyed.

“It was a lot of work yesterday and tremendous effort, and it paid off,” Reitz said.

But the mushroom-like cloud that formed nearby has added another element to the usual volatility of fighting fires. Pyrocumulus clouds form from fire and collapse onto themselves, causing the weather conditions to change.

“It’s all heat, toxins and smoke,” said Capt. Scott Visyak of the California Department of Forestry and Fire Protection.

Fed by dry fuel on steep slopes, the fire headed into Apple Canyon and Bonita Vista, and new evacuations were announced for McCall Park, south of Pine Wood, Cedar Glen, Pine Cove and Fern Valley.

Steve and Suzanne Coffer were on their way to San Diego to hit the casinos when approaching flames made them return home to hurriedly pack up their belongings. They spent the night in their car with their cat, parked near a church.

When they saw their house again, it was coated in retardant. The mess was no matter for Steve Coffer, who had moved to Idyllwild 40 years ago, yearning for a place far from the city.

The elation at finding his home still standing was difficult for him to express.

“I can’t put it into words.”

Many residents were without power, including Ruth Kleefisch, 52, who drove from her home in Pine Cove to Idyllwild in an attempt to charge her cellphone and try to get reception.

Kleefisch’s husband has liver cancer and has been unable to eat for the last four days. She was desperate to reach his doctor to ask what she could do to help her husband’s nausea.

She said she was less concerned about the fire, which hadn’t reached Pine Cove, and more concerned about being without power, especially if it lasted more than a few days.

“The neighborhood’s quiet, everything is quiet. There’s nobody here. Once all the tourists leave, there’s not that many left of us, really.”

Fires have also struck Northern California, where firefighters work in brutal 110-degree temperatures on the northern edge of the Sacramento Valley. Crews scrambled when a shift in the winds pushed the Carr fire three miles east in four hours, catching residents in Whiskeytown on their heels.

The blaze reached the edge of Whiskeytown Lake, where local news outlets reported that 40 boats were burned along with a number of homes.

Authorities placed 192 homes under mandatory evacuation orders, most of those in Whiskeytown and the community of French Gulch, the California Department of Forestry and Fire Protection said.

The blaze was 20,000 acres and 10% contained Thursday morning. But most of that containment was on the fire’s west and northwestern edge, not on its southern face where the residents are, said spokesman Chad Carroll. The blaze has been running along the north side of Highway 299 since a vehicle malfunction sparked it Monday afternoon, he said.

While the Carr fire has been fueled by wind and topography, the Ferguson fire outside Yosemite National Park has been decidedly different, said U.S. Forest Service spokesman Jacob Welsh.

Crews in the rugged forests in Mariposa County have been dealing with an inversion layer that has put the Ferguson fire’s smoke right on top of Yosemite Valley and other low-lying areas. Poor air quality and visibility have limited the ability for planes and helicopters to help fight the fire, Welsh said. At the same time, that smoky blanket keeps the fire from “getting a breath of fresh air” and growing, Welsh said.

One of the biggest obstacles to containing the fire continues to be the terrain, a mix of steep cliffs with deep, inaccessible canyons loaded with vegetation and slopes of standing dead trees — victims of a bark beetle infestation that’s killed 129 million trees since 2010.

The Ferguson fire was 43,299 acres and 27% contained, officials said.

The strategy with the Cranston fire is to hack away at flammable vegetation along its perimeter to cut off the fuel supply, said Kate Kramer, a spokeswoman with the San Bernardino National Forest.

Farther out from the fire line, she said, firefighters are clearing flammable brush to prevent it from spreading.

The blaze is being directly attacked in areas covered in extremely dry grass, where the fire burns quickly and stays low enough to be extinguished safely.

jaclyn.cosgrove

@latimes.com

laura.newberry

@latimes.com

corina.knoll@latimes.com

joseph.serna@latimes.com

Cosgrove reported from Mountain Center, Newberry from Banning, and Knoll and Serna from Los Angeles.