A wildfire in Oregon that has been burning for weeks was found to have been ignited by lightning, and smoldered for days before it was detected.
That's according to forest officials on Wednesday.
The so-called Bootleg fire is the largest of dozens of wildfires currently burning across the United States.
Its origin came to light as ground crew of more than 2,000 people made increasing headway in curtailing the blaze.
They were helped by calmer winds, cooler temperatures and a slightly higher humidity over the past two days.
Officials say the blaze is now growing at a slower rate, as it enters an area with less vegetation to burn.
But the fire is still on-track to becoming the state's third-largest on record since 1900.
It has so far burned through an area well over half the size of Rhode Island -
nearly 400,000 acres of tinder-dry brush and timber.
It is so large that it's even generating its own weather, capable of spawning lightning storms which can in turn ignite new fires.
No fatalities or serious injuries have so far been reported.
But dozens of homes and more than 100 outbuildings have been destroyed.
The Bootleg fire adds to an unusually heavy start to the Western fire season, with about 80 major active wildfires reported in 13 Western states this week.
More than 1.3 million acres of land has already been scorched.
Experts have attributed the extreme weather to climate change.