A tractor-trailer caught fire on the side of the freeway and quickly spread to dry vegetation in hot weather. Flames scorched 50 acres.
The fire is 80 percent contained, and full containment was expected by the end of the day. There were no open flames, but crews were watching for flare-ups in the burn area.
No damage or injuries were reported.
Fire officials are concerned about the early start to wildfire season. They say the hills don't usually see these dry and hot conditions until July.
The Associated Press contributed to this report.