The accident Sunday occurred when the fire engine's drive train malfunctioned, said Highway Patrol Officer Karen Faciane. With its siren blaring and lights flashing, it veered across three southbound lanes of Interstate 15 and rolled down an embankment, officials said.
The driver was in critical condition with a broken pelvis and the two other firefighters had moderate injuries, Faciane said.
The firefighters were traveling to a blaze in Calimesa, Calif., about 30 miles west of Palm Springs, that had torn across 500 acres by early Monday morning.
The blaze, which was 10 percent contained, damaged a garage but had not destroyed any homes, said Michelle McClelland, a spokeswoman with the California Department of Forestry.
In Oregon, hot, dry and windy weather was moving into southwest Oregon, where firefighters battled the state's largest wildfire in more than a century.
The fire, which had burned nearly 376,500 acres by Monday morning, was threatening power lines that supply several northern California towns including Crescent City.
Full containment for the section of the fire south of the California state line was expected by Thursday. The rest of the fire was only about 25 percent contained.
During the weekend, crews created three or four fire lines in front of the flames west of O'Brien, Ore., but said they would have to ask Pacific Power to shut down the power lines if the wildfire got too close. Heavy smoke can create short circuits, producing electrical arcs that could endanger firefighters.
In southern California's eastern San Diego County, a 62,000-acre wildfire that started two weeks ago and had destroyed dozens of homes was 85 percent contained. Full containment was expected Monday evening instead of Sunday as previously predicted, said Forestry Department spokeswoman Audrey Hagen.
Meanwhile, researchers investigating the aftermath of major wildfires say they now believe most houses are destroyed by errant embers, burning after the main fire has swept through.
The discovery could change the way firefighters combat wildfires, said Jack Cohen, a fire behavior scientist at the U.S. Forest Service Fire Sciences Laboratory in Missoula, Mont.
"We get the sense that it all happens at once, that the whole neighborhood explodes into flame, and that's not necessarily the case," Cohen said.
The discovery means if firefighters can safely wait out the speeding front of a wildfire — the so-called "crown fire" — they can snuff small sparks that pose the larger threat to homes afterward.