On a checkerboard of destruction, where burned homes represented the black squares, Rolland Crawford looked for the familiar patterns of a country fire turned city fire. He found them in the torched eucalyptus and palms, the seared roof vents, the charred eaves.
"This is what you call an urban conflagration," said Crawford, the fire chief of Loma Linda and an expert in how flames march from overgrown hillsides into paved flatlands.
He was touring the gutted homes on San Bernardino's 39th Street -- outside his jurisdiction but right in the middle of where last month's wildfire stormed into the city, providing fresh lessons in his specialty.
About 250 homes that went up in smoke on 39th Street and others like it had seemed a safe distance from the blazing mountains. Most were not near brush, were clad in fire-resistant shingles and were accessible on broad roads with plenty of room for engine companies and their hoses.
Many also stood next to homes that survived, creating that mosaic of ruin and reprieve.
It was the little things -- the trees, the vents, the eaves -- that helped doom the lost homes, Crawford and his colleagues said. They described them as everyday hazards that typically go unnoticed by homeowners, until a disaster like the Old fire lays them bare.
The flames raged through the San Bernardino back country for two weeks, consuming 91,000 rugged acres. They flared into the city within 75 minutes of igniting, then rode powerful winds in and out of San Bernardino proper for two days, overwhelming the resources arrayed against them.
"There was no way to put firefighters out in front of it," Crawford said. "It's not a suicide mission."
Down below, the wildfire became a series of structural blazes, fed by fuels that beautify neighborhoods even as they endanger them.
"See the eucalyptus there?" asked David Neff, a deputy fire chief for the California Department of Forestry and Fire Protection who joined Crawford for the tour. Neff was driving up Del Rosa Avenue, pointing to a line of trees that stretched from the unpopulated hills to the homes on level ground.
All the eucalyptus had burned.
"They threw firebrands down from the mountain," Neff said, referring to large embers. "See the palm trees?"
He nodded toward a similar scene, a rank of palms marching like pickets from the ridge into the town, their fronds and skirts incinerated.
Eucalyptus and palms are notorious fire accelerators because of their flammable oil and shaggy crowns, respectively. When burning in high winds, both shoot embers across a wide area, which can touch off more trees and homes as much as two miles ahead of the main fire -- a phenomenon known as spotting.
"The initial wave of flame hits all the houses right up against the edge of the hills," said Clyde Chittenden, a fire battalion chief for the state forestry agency. "Then you have firebrands flying through the air, and fingers of the wave follow them."
Chittenden said that is probably what happened to 40% of the homes that burned in lower San Bernardino. The rest were probably in the direct path of the fire as it moved from house to house, some of them exploding into flames just from the radiating heat, he said.
"This was one hot street," Neff said to Chittenden.
With Crawford, they were examining a pile of debris that was once a home on Delmonica Avenue. The yard had been covered from curb to door with juniper, another fire-nourishing plant. The three fire chiefs speculated that an ember lighted the juniper, which -- like a fuse -- sent flames racing to the house.
"Juniper looks like a house afire when it burns, it has so much oil in it," Crawford said.
Across the street, the fire had wiped out a bed of ice plant and scorched two palms, but left the house alone. The chiefs said it appeared the home had been spared because the greenery had been trimmed back from it.
"Any plant will burn. Look at this," Neff said, holding up a wedge of singed ice plant still dripping its sap.
If it isn't the foliage, Neff and his colleagues said, it's the small structural features that can imperil a house.
"Like those twirly vents," said Crawford, directing the group's attention to a spinning rooftop vent a couple of houses away.
He told of another home where that type of open vent had served as a vacuum for embers, sucking them into the attic. The homeowner had saved the house with his garden hose.
"Vents should have screens with mesh a quarter-inch or smaller," Crawford said.
On 39th Street, he focused on a house that had started to burn from the top down. Two-thirds of its roof had caved in. "An ember probably got in through a dormer vent," he said.
Or maybe it flew up under the eaves, Neff said.
Like most older homes, the house had exposed wooden eaves, which are perfect for trapping embers and will smolder until the roof erupts in flames. Bird nests and spider webs in such eaves act as kindling.
That's why eaves on newer homes are enclosed in stucco or other fire-retardant materials, the chiefs said.
Even new homes, however, can have flaws that invite destruction, they said. Crawford is particularly worried about vinyl window frames, which provide better weather insulation but melt faster than wooden ones burn.
When an approaching fire softens the vinyl -- at about 350 degrees; wood ignites at 450 to 500 degrees -- the windows fall out and the flames rush into the house, he said.
"The frames were an excellent idea from an insulation standpoint," Crawford said, "but from a fire perspective, it just isn't working."