An undetermined roadside ignition off the Ventura (101) Freeway in the Conejo Grade sparked the Springs Fire, officials said on Sunday.
Officials are calling it an "undetermined roadside ignition of grass and debris" that started the region's largest wildfire so far this year that scorched nearly 44 square miles along the Ventura and Los Angeles county lines.
“Undetermined is a very broad spectrum. So, they couldn’t find something specific that caused the fire," said Tony McHale, with the Ventura County Fire Department. "Examples of the kinds of things that we find along the highway – large metallic items that fall off vehicles, these things can cause sparks. Sometimes there’s discarded cigarettes."
Now that firefighters have the Springs Fire nearly under control after three days fighting in steep, rugged and rocky terrain, the focus of the blaze turns to a grassy area off the Ventura Freeway in the Conejo Grade where the fire was sparked on May 2.
Full Coverage: Southern California Wildfires
The fire began off the southbound side of the Ventura Freeway at Camarillo Springs Road. The fire quickly spread to over 28,000 acres of the Santa Monica Mountains in near triple-digit heat and low humidity.
It was 75 percent contained by Sunday evening with full containment expected by Monday.
Some 15 homes and several recreational vehicles were damaged and several communities in the path were evacuated.
Five firefighters suffered minor injuries, according to the Ventura County Fire Department. Two of the first responders suffered wounds from falls, and three had debris in their eyes.
The fire prompted a massive mutual-aid response from agencies across the state.
At one point, 1,900 firefighters -- assisted by water-dropping and fire-retardant dropping planes and helicopters -- attacked the flames.