Their beards dripped with sweat and ash. They lumbered ahead with fatigue and concern: The fire was just a few miles from their hometown.

The hotshot crew from Big Bear, Calif., pushed along the steep, smoky ridge after a long night battling a blaze that spread fast, burned hot and just would not die.

“This area’s burned a lot more than we thought it would for this time of year,” said Ryan Doyle, 38, one of the firefighters hiking along a canyon of smoke and flame. “For the last couple of years, they’ve been saying it’s really bad, but this is the year I think we might really see it.”

The Lake Fire started just before 4 p.m. on June 17. If rain and snow had arrived as scheduled in the winter, it might have been done in a day, at a cost of just a few acres. But with the drought turning soil to dust and trees to tinder, the fire, still smoking, has consumed a swath of national forest roughly the size of San Francisco.

It has become the first big wildfire of a California season that threatens to become a terror. Between Jan. 1 and July 11, California fire officials have responded to more than 3,381 wildfires, 1,000 more than the average over the previous five years.

The map below shows this year’s fires, as detected by satellite. There are blazes big and small all across the West, but wildfires have been especially concentrated along the mountain ranges of central California.

Fire locations, Jan. 1 to July 9 Salt Lake City UTAH NEV. Denver COLO. San Francisco Las Vegas CALIF. ARIZ. Santa Fe Lake fire N.M. Los Angeles Phoenix 100 MILES Fire locations, Jan. 1 to July 9 San Francisco CALIF. Los Angeles Lake fire 100 MILES Fire locations, Jan. 1 to July 9 CALIF. Salt Lake City UTAH NEV. Denver COLO. San Francisco Las Vegas ARIZ. Santa Fe Lake fire N.M. Los Angeles Phoenix 100 MILES

Sources: U.S.D.A. Forest Service Remote Sensing; NASA

In the forests outside San Bernardino, the drought’s impact was hard to miss. Stomping down the dirt trails leading into the Lake Fire meant breathing in a fine dust, as dry as that of an Iraqi desert. The leaves of otherwise moist vegetation like Manzanita, an evergreen shrub, crunched rather than bent, and much of the wood on the ground was dry and light, some as airy as Styrofoam.

It was all the product of rain – or rather, the lack of it. Rain, once plentiful, has maintained its absence, falling so rarely that huge sections of Big Bear Lake where fish used to dart and birds once nested are now wide-open, empty meadows.

Rainfall in California, three-year averages, October to September 1960-63 21 inches 1981-84 32 inches 2011-14 15 inches Rainfall in California, three-year averages, October to September 1960-63 21 inches 1981-84 32 inches 2011-14 15 inches

Source: Western Regional Climate Center

For those who know fire, fuel is now all they see.

When Nick Bruinsma, a Big Bear firefighter and spokesman for the United States Forest Service during the Lake Fire, stood on a ridge at the fire’s edge, it took him only a moment to interpret the smoke rising from the miles of mountains before him.

He pointed to the light gray puffs, identifying the source as burning underbrush. Then he turned his attention to the darker clouds rising in narrow plumes. “That’s a good clump of trees right there,” he said. He explained how the color of the smoke corresponds to the density of the fuel.

He described how fire – in such arid conditions – climbed quickly up mountain ridges and spread vertically, going from the grasses at ground level to smaller branches that act as ladders to the bodies of dry trees.

Dead trees were, in part, what allowed the fire to keep going. And they can be found all over California.

The Forest Service conducted aerial surveys in April, flying over the most drought-stricken land several months earlier than normal this year, in response to reports from the field that more trees had died.

They found a sizable increase in tree deaths statewide, mostly in the Sierra Nevada.

Last summer, officials recorded 110,000 tree deaths in that area of California.

CA Dead trees per acre in 2014 Detail 3 6 10 15 N 20 MILES Dead trees per acre in 2014 3 6 10 15 CA Detail N 10 MILES Dead trees per acre in 2014 CA 3 6 10 15 Detail N

When they returned to the same area this spring, they recorded 2.3 million tree deaths. In all, they identified 12.5 million dead trees in a million acres of California land.

Dead trees per acre in 2015 3 6 10 15 Dead trees per acre in 2015 3 6 10 15 Dead trees per acre in 2015 3 6 10 15

Source: United States Forest Service, Forest Health Aerial Survey Program

Not surprisingly, given the conditions, fire season in recent years has lasted longer than usual. A generation ago, firefighters could expect the season to last a couple of months. Not anymore.

A study from the University of California, Merced, has shown that fire seasons in the West, including California, are, on average, 86 days longer than they were in the 1970s.

“Southern California has a 12-month fire season now,” said Scott L. Stephens, a professor of fire science at the University of California, Berkeley. “You can have a fire there at any time.”

Length of fire season, for fires larger than 1,000 acres In California In all Western States 1973-1982 78 days 147 days 1983-1992 86 201 1993-2002 120 223 2003-2012 143 233 Length of fire season, for fires larger than 1,000 acres In California 1973-1982 78 days 1983-1992 86 1993-2002 120 2003-2012 143 In all Western States 1973-1982 147 days 1983-1992 201 1993-2002 223 2003-2012 233

Source: A. LeRoy Westerling, University of California, Merced

The work of firefighting has become more intense, too. Fires flush with fuel burn hotter. A lack of humidity, both day and night, only adds to the risk.

Firefighters like Justin Pickens, 28, above, admit that drought-era firefighting takes a heavy toll.

But firefighters are not the only ones affected. The Lake Fire used up tens of thousands of gallons of water, if not more, and though some of it was recycled wastewater, California officials are increasingly concerned that water will be in short supply, or harder to obtain, as fire season continues.

Taxpayers will foot the bill. In July, the total cost of the Lake Fire approached $40 million. “Fire suppression costs are skyrocketing,” Mr. Stephens said. “You have all these people living around these fires; you have structural protection and it all makes suppression costs go up exponentially.”

Projections show that the cost of fighting wildfires this year could reach up to $2.1 billion, far above the roughly $450 million spent annually in the 1990s.

Fire suppression costs, in billions $2.0 1.5 1.0 0.5 1985 1995 2005 2015 projected range Fire suppression costs, in billions $2.0 1.5 1.0 0.5 1985 1995 2005 2015 projected range

Sources: United States Department of the Interior; National Interagency Fire Center

Residents and firefighters, usually skeptical of dire fire warnings, have become more anxious.

During the Lake Fire, some people in and around Big Bear took to ignoring warnings about conserving water, hosing down their homes.

Others made extended plans to flee, to one house, then another – they said they expected more fires, and more rounds of moving as the season continues.

“I’ve been running camps for 20 years and the fires used to come a lot later,” said John Fisher, the manager of a Y.M.C.A. summer camp that was evacuated during the blaze. In the distance, smoke from the fire colored the sun. “This is the first time we’ve had to evacuate this camp in more than a decade,” he said.

Mr. Stephens said that California’s forests need more gaps between clustered trees to limit fire’s spread. But as teams of firefighters finally took control of the Lake Fire, the future looked bleak. Four years of drought, along with climate change, had turned what should have been cool and moist higher elevations into a tinderbox, and then a burned-out moonscape of ash and wooden skeletons.

Samantha Fausel, 25, a firefighter from Cleveland National Forest in San Diego, said their commanding officers had warned that the probability of ignition was still 100 percent. Hundreds of miles away in other California forests, warnings for the coming months have been just as ominous.

“Fire is relentless,” Ms. Fausel said, a chain saw slung over her shoulder. “There’s only so much you can do. Sometimes you have to just sit back and watch. It’s just that intense.”