By Paige St. John

It was a stubborn, quick wildfire, but nothing particularly unusual.

Dubbed the Rocky fire, it started Wednesday near the shore of Clear Lake, about 110 miles northwest of Sacramento. Since then, a growing number of firefighters had worked in steep, rough terrain to get a handle on the blaze as it continued to grow and threaten rural communities.

Then came Saturday.

With temperatures climbing into the triple digits and humidity near zero, the fire exploded, charring 20,000 acres in one five-hour stretch that a fire official called "historic, unprecedented." Throughout the night, when wildfires typically lay down in the relative cool, the Rocky fire continued to rage.

With the traditional fire season having only recently begun, the intensity of the Rocky fire, along with other major blazes burning throughout the state, has upended long-held expectations and predictions. The unrelenting drought that has parched the state for the last four years has altered the landscape dramatically.

"The brush and the vegetation is so tinder dry that what we've been seeing in the past couple weeks is that fires are able to burn at such an explosive rate and intensity that we wouldn't see until later in the year," said Daniel Berlant, spokesman for the California Department of Forestry and Fire Protection. "There is a concern there that this type of rapid growth fire this early in the season is the new normal."

By the time the sun rose Sunday, the Rocky fire had nearly doubled in size from the previous night. Its pace slowed somewhat, but it continued to grow, charring 54,000 acres by late in the evening. Firefighters had managed to reach 5% containment, officials said.

At least two dozen homes and a similar number of outbuildings had been destroyed, and 6,000 more structures were threatened, according to figures released by the U.S. Forest Service early Sunday.

Nearly 2,000 firefighters were battling the fire -- a number that officials said could rise in coming days.

No injuries had been reported, which Berlant called "a miracle," given the fire's aggressiveness and the hazards of the terrain.

But the blaze wrecked havoc on communities scattered throughout the idyllic lake region. Officials closed state highways as firefighters tried to use the swaths of pavement to disrupt the fire's push forward.

About 12,000 people had been told to evacuate their homes and campgrounds. A shelter was opened at a local high school and the displaced snapped up hotel rooms, said Margot Simpson, a shelter manager for the American Red Cross.

At a community meeting Sunday, fire officials briefed residents on the fire's progress. Frustrated by conflicting information on social media, many in attendance pleaded for information about whether the fire had reached their neighborhoods.

Richard Hardie said he rebuffed three earlier efforts by firefighters to get him to leave his home, but relented Saturday when sheriff's deputies ordered him to evacuate. With his medicines and some possessions packed in a small bag, Hardie said he hadn't been able to corral his cats, which ran off when the deputies came knocking.

"I'm concerned about my place, but I feel safer here," Hardie said of the shelter.

Elizabeth Ormsbee, 14, and her family fled their home Friday as flames appeared on a nearby ridge. "I was crying, but a firefighter talked to me and he told me it would be OK," she said.

Elizabeth said she has been staying with her godmother, Cindy Burton, in nearby Clear Lake. Ash and smoke have periodically descended on the small town, depending on the direction of the wind.

"We're all praying it gets put out soon," said Burton, who helped organize a group to make signs thanking firefighters that it posted at the county fairgrounds, which is serving as the command center for the several agencies involved in battling the fire.

But a quick end seemed out of the question as firefighters struggled to get an upper hand on the blaze.

Berlant described what he said were dangerous and unstable conditions for fire crews as winds whipped flames into mini-tornadoes and embers shot forward from the flames, igniting vegetation and trees farther ahead.

On Saturday, work crews used bulldozers to dig break lines in an effort to stop the fire from advancing to the north and east. When the lines proved useless, firefighters were forced to retreat a few miles to California 20 to the north and California 16 to the east. There they set controlled grass fires along the highways to create charred strips that they hoped would be wide enough to stop the fire's advance.

They worked desperately throughout the day Sunday to keep the fire's northern front from jumping the highways. By evening, however, officials said it seemed likely the effort would fail, at least to the north.

"This fire is doing things that nobody's ever seen before," said Jason Shanley, a Cal Fire spokesman. "It took a few days to get to 20,000 acres, and all of a sudden, in five hours, it burns to 40,000 acres. Where does that happen except for on TV?"

The plume of smoke from the blaze reached Sacramento, where health officials announced air advisories for people with respiratory problems.

It was the largest of several major blazes burning throughout Northern California and Oregon. Those fires, along with scores of smaller ones, were straining resources as local, state and federal fire officials raced to dispatch adequate manpower and machinery to the growing number of blazes.

On Friday, Gov. Jerry Brown declared a state of emergency to expedite the response.

"Dry thunderstorms" -- lightning and wind with very little rain -- were to blame for much of the destruction, officials said.

Weather was not the only culprit, however. A woman was arrested Thursday on suspicion of causing a 200-acre fire near Groveland, just outside Yosemite National Park. And farther south, near Bass Lake, authorities say a boy playing with a lighter started a fire that led to the evacuation of about 200 homes.

Chirbas reported from Lakeport, St. John from Sacramento and Rubin from Los Angeles.

(c)2015 the Los Angeles Times