MIDDLETOWN, Calif. — The massive Mendocino Complex fire jumped across at least four creeks, one major road and a fire line cut by a bulldozer in a single six-mile run this weekend toward Leesville, a tiny unincorporated way station in Colusa County.

Typically, any one of those breaks could have halted the spread of wildfire. But shifting winds and brittle-dry vegetation sent flames — up to 300 feet high in some areas — leapfrogging in all directions in three Northern California counties and on both sides of scenic Clear Lake, past these man-made and natural obstacles. The erratic conflagration has chewed through more than 266,000 acres and 68 homes in 10 days, making it the fourth-largest wildfire on record in California.

It was expected to become the third-largest by Monday morning, and fire officials say it could easily climb to the top of the list, surpassing the Thomas fire that burned 281,893 acres in Ventura and Santa Barbara counties in December.

“It is extremely fast, extremely aggressive, extremely dangerous,” said Scott McLean, a deputy chief with the California Department of Forestry and Fire Protection. “Look how big it got, just in a matter of days.… Look how fast this Mendocino Complex went up in ranking. That doesn’t happen. That just doesn’t happen.”

The progression has been relentless. The Ranch and River fires, which may join at Clear Lake and are together known as the Mendocino Complex, are tearing through tens of thousands of acres a day, including overnight when fires normally calm down. The fire, which was 33% contained Sunday night, is raging in remote areas and therefore hasn’t been as destructive to property as some of the other dozen-plus wildfires burning across the state. But its sheer size and rate of spread is the latest signal of a remarkable fire year for California.

“We're at the mercy of the wind,” said Garden Grove Fire Capt. Thanh Nguyen, who is acting as a spokesman for Cal Fire in Middletown in Lake County. “Tragically this whole area is really dry, and once you get the lighter fuel going, that preheats the denser fuel, and then it's really difficult for them to put out.”

Lake County has been particularly hard hit by wildfire in the last five years. Two years ago, the Clayton fire tore through almost 4,000 acres and 300 structures, many of them mobile homes and rentals. The blaze hit the town of Lower Lake particularly hard, destroying a 150-year-old church and a Habitat for Humanity office. The wildfire followed three that ripped through Lake County in 2015, including the Valley fire, which destroyed more than 1,300 homes and killed at least four people.

UCLA climate scientist Daniel Swain cited several factors for the destruction in Lake County: explosively flammable vegetation, warm overnight temperatures and the lingering effect of years of drought.

“This is a part of the state that I think that overnight temperatures have played an enormous role,” Swain said. “It’s sort of this middle elevation where you’re above the marine layer but you’re not high enough in the mountains to really cool down either. So you’re sort of in this zone where fires can burn, with the increase in temperatures, as we’ve seen, all day and all night.”

A decade ago, some scientists would warn against making broad conclusions linking an extraordinary heat wave to global warming. But the pace of temperature records being broken in California in recent years is leading more scientists to assertively link climate change to unrelenting heat that is only expected to worsen as humans continue putting greenhouse gases in the air.

“In the past, it would just be kind of once in a while — the odd year where you’d be really warm,” state climatologist Michael Anderson said.

Over the weekend, fire crews tried laying contingency lines behind their fire lines, hoping to slow the spread of the fire. On Saturday, flames jumped a line of bulldozer-scraped dirt on Long Valley Ridge meant to protect the lakeside community of Lucerne. The breach set off a scramble of firefighters down Highway 20 to protect the community. Fire crews began bulldozing a second containment line outside the town, and firefighters were trying Sunday afternoon to hold the line at High Valley Road.

“It’s really taking off in a huge way,” Swain said.

The fire Sunday moved into sparsely populated ridges to the north and east in Mendocino National Forest and crossed into Colusa County, prompting emergency officials in adjacent Glenn County to issue an evacuation advisory for people living a dozen miles away. Two fingers of the Ranch fire made a run toward Leesville, hopping bulldozer lines, creeks and roads.

At a reservation along the northern end of Clear Lake, an area that has been buffeted by major fires since 2015, including the devastating wine country fires last summer that blitzed through Napa Valley, some four dozen members of the Robinson Rancheria tribe of Pomo Indians took a stand against the burning mountain, plowing fire lines and cutting brush. They were armed with two tractors, weed whackers, borrowed water tanks and hoses — some of which were left behind by the Red Cross after the last fires.

Most of the men and women who stayed behind at the 720-acre reservation vowed to stay and fight if the fire crested Hogback Ridge and came at them, the casino, the gas station, gym and cluster of 55 houses. The rancheria is wedged between the ridge and the lake, and at one point with fire both to the north and south, it was in danger of being surrounded by flames with no escape route.

But in the past, those residents who vowed to stay had to fight back only small grass and brush fires that encroached on the tribal land, said E.J. Crandell, 41, chairman of the Robinson Rancheria tribe of Pomo Indians. “They are thinking like, this is a wild dog,” he said, referring to past fires. But the Mendocino Complex fire, he said, “is a wolf.”

Crandell said he would like to spend a summer reducing undergrowth and dead wood and creating fire breaks.

“Preventative measures — these things would be no problem,” he said. “But our county, there’s been so many fires. After each one we do a plan to fix the conditions — and before we can do that, there’s another fire. So we never get a chance to start from the bottom up.”

Farther north, near Redding, residents began returning to neighborhoods ravaged by the Carr fire, which has been linked to seven deaths, destroyed more than 1,000 homes and consumed more than 160,000 acres. Crews have reached 43% containment but have been hampered by steep, rugged terrain, blistering temperatures and bone-dry vegetation.

“Progress has definitely been slow on this fire because of the difficulties we’ve had,” said Gabe Lauderdale, a spokesman for Cal Fire. “But progress is still steady.”

More than 15,000 firefighters are battling 18 large wildfires across the state that have burned more than 559,000 acres and are threatening 17,000 homes. As of a week ago, Cal Fire crews had responded to 330 more wildland fires so far this year than by this time last year, McLean said.

In Mariposa County, the Ferguson fire has burned nearly 90,000 acres and has left parts of Yosemite National Park, including tourist draw Yosemite Valley, closed indefinitely. The blaze has burned dead trees that can become explosive and fall without warning, posing a risk to firefighters, park officials said. A firefighter battling the blaze was killed a week ago by a falling tree.

“They’re working,” he said. “They’re working hard.”

paige.stjohn@latimes.com

alene.tchekmedyian@latimes.com

ron.lin@latimes.com

St. John reported from Middletown, Tchekmedyian from Los Angeles and Lin from San Francisco.