QUINCY, Calif. (AP) — Johnnie Brookwood had never heard of a road named Dixie when a wildfire began a month ago in the forestlands of Northern California.

Within three weeks, it exploded into the largest wildfire burning in the U.S., destroying more than 1,000 homes and businesses including a lodge in the gold rush-era town of Greenville where she was renting a room for $650 per month.

“At first (the fire) didn’t affect us at all, it was off in some place called Dixie, I didn’t even know what it means,” Brookwood, 76, said Saturday. “Then it was ‘Oh no we have to go too?’ Surely Greenville won’t burn, but then it did and now all we can see are ashes.”

Firefighters faced “another critical day” as thunderstorms pushed flames closer to two towns not far from where the Dixie Fire destroyed much of Greenville last week.

Wind gusts of up to 50 mph (80 kph) also pushed the fire closer to Janesville, a town of about 1,500 people, east of Greenville, said Jake Cagle, the operations chief at the east zone of the fire.

“Very tough day in there yesterday in the afternoon and the night (crew) picked up the pieces and tried to secure the edge the best they could with the resources they had,” he said in a briefing Saturday.

With a similar forecast of thunderstorms Saturday, firefighters faced “another critical day, another challenging day,” Cagle said.

The fire was among more than 100 large wildfires burning in more than a dozen states in the West seared by drought and hot, bone-dry weather that turned forests, brushlands, meadows and pastures into tinder.

The U.S. Forest Service said Friday it’s operating in crisis mode, fully deploying firefighters and maxing out its support system.

The roughly 21,000 federal firefighters working on the ground is more than double the number of firefighters sent to contain forest fires at this time a year ago, said Anthony Scardina, a deputy forester for the agency’s Pacific Southwest region.

More than 6,000 firefighters alone were battling the Dixie Fire, which has ravaged nearly 845 square miles (2,100 square kilometers) — an area the size of Tokyo — and was 31% contained.

The cause of the fire has not been determined. Pacific Gas and Electric has said the fire may have been started when a tree fell on its power line.

There also was a danger of new fires erupting because of unstable weather conditions, including extreme heat across the northern half of the West and a chance of thunderstorms that could bring lightning to Northern California, Oregon and Nevada, according to the National Interagency Fire Center.

In southeastern Montana, firefighters were gaining ground on a pair of fires that chewed through vast rangelands and at one point threatened the Northern Cheyenne Indian Reservation.

The fires were caused by heat from coal seams, the deposits of coal found in the ground in the area, said Peggy Miller, a spokeswoman for the fires.

Mandatory evacuation for the tribal headquarters town of Lame Deer remained in place due to poor air quality, she added.

Smoke also drove air pollution levels to unhealthy or very unhealthy levels in parts of Northern California, Oregon and Idaho, according to the U.S. Air Quality Index.

Hot, dry weather with strong afternoon winds also propelled several fires in Washington state, and similar weather was expected into the weekend, fire officials said.

In southeastern Oregon, two new wildfires started by lightning Thursday near the California border spread rapidly through juniper trees, sagebrush and evergreen trees.

The Patton Meadow Fire about 14 miles (23 kilometers) west of Lakeview, near the California border, exploded to 11 square miles (28 square kilometers) in less than 24 hours in a landscape sucked dry by extreme drought. It was 10% contained.

Triple-digit temperatures and bone-dry conditions in Oregon could increase fire risks through the weekend.

Climate change has made the U.S. West warmer and drier in the past 30 years and will continue to make the weather more extreme and wildfires more destructive, according to scientists.

Dozens of fires also are burning in western Canada and in Europe, including Greece, where a massive wildfire has decimated forests and torched homes.