All the ingredients were there. Dry heat, gusting winds in a mountain pass cloaked in dead grass and drought-shriveled chaparral.
All it needed was a spark. It came at 10:36 Tuesday morning near Kenwood Avenue west of Interstate 15. The Blue Cut fire was born.
"It all aligned. The wind, the fuel and the topography," said Capt. Howard Deets of the Mill Creek hotshot crew based in the San Bernardino National Forest. "When that happens there's nothing you can do about it. You could throw the world's fire fighting resources at it and it's just going to keep going."
That's what the Blue Cut did, chewing through 25,626 acres by Wednesday night, forcing mass evacuations and shutting down one of the most heavily used routes through the mountains that form the untamed backdrop to the sprawl of the Los Angeles Basin.
The terrain near where the fire started is so rugged and steep that "it's like wadded up paper" said incident commander Michael Wakoski, a battalion chief with the San Bernardino County Fire Department. "It's almost impossible to move up and down the slopes. It makes containment of the fire very difficult."
When firefighters arrived Tuesday morning, a freight train stood idle on the tracks, abandoned by the engineer, who fled the fast-moving fire.
Gusts of 20 to 30 mph pushed the blaze north in the Cajon Pass, a natural wind tunnel, tossing embers a half-mile ahead of the flame front. The fire jumped the freeway.
Firefighting crews were left on the defense, struggling to protect homes as flames consumed chaparral, pine trees and yucca.
"We got our butts kicked," Wakoski said.
The firefighting effort is complicated by the patchwork of crucial infrastructure that runs through the pass: Electrical lines that provide power to the basin, rail lines, high-pressure gas lines, a fiber-optic network — even a pipeline that carries jet fuel.
The cause of the blaze is under investigation, but most wildfires in Southern California are caused by people, accidentally or intentionally. According to Caltrans, an average of 156,000 vehicles a day pass the Kenwood Avenue area — a endless source of sparking tail pipes, engine fires and discarded cigarette butts.
Richard Halsey, director of the California Chaparral Institute, drove through the pass earlier this summer.
"It was very stunning to me to see how much of that landscape through the Cajon Pass had been burned multiple times and was filled with invasive grasses."
Native chaparral shrubs can't survive repeated fires over a short time span. They yield to invasive grasses that ignite easily and burn quickly, increasing the fire threat.
"It's not how we fight the fires. It's how do we stop them from starting in the first place," argued Halsey, who thinks Caltrans should consider placing concrete K-rail barriers along the freeway in the pass to stop sparks from flying into roadside vegetation.
The Blue Cut fire is but the latest reminder that "we're living where it burns," said Char Miller, a Pomona College professor of environmental analysis. Noting the huge evacuations ordered for the fire — some 83,000 people have been told to leave their homes — he questioned the wisdom of allowing so much development at the edge of high-fire zones.
"We don't allow it in flood plains, we prevent earthquake damage, but we don't do it with fire," he added.
Five stubborn years of drought have made Southern California's naturally flammable landscape even more fire prone.
"We have an amazing amount of standing dead shrubs in addition to extraordinarily low live-fuel moisture," noted Marti Witter, a fire ecologist with the Santa Monica Mountains National Recreation Area.
"I'm really, really concerned about what's going to happen" this fall if the region doesn't get early rains and it's a season of strong Santa Ana winds, she said. "We would be lined up for another firestorm year."
Jennings and Esquivel reported from Lytle Creek, Boxall from Los Angeles. Times Staff writer Sarah Parvini contributed to this report.
MORE ON BLUE CUT FIRE
7:25 p.m.: This article was updated with additional details on the size of the fire.