Firefighters in Redding have extinguished four spot fires along Interstate 5 near Hilltop Drive.
The fires were reported around 9:30 a.m. on Friday, along the northbound lanes.
Firefighters quickly extinguished the fires in about 10 minutes.
One northbound lane of Interstate 5 was closed to allow fire crews to access the scene. Traffic was slowed in the area.
Initially there were reports of a suspicious person in the area.
A man was detained at the scene but investigators said he was cooperative and believe he was simply in the area at the time.
On Friday afternoon Redding Fire Prevention Division Chief Mike Bachmeyer said while they will never know the exact cause of the fire, they believe it might've been sparked by a vehicle.
A piece of a catalytic converter , part of the exhaust system, was found in the area.
At one point nine engines responded.