LIVERMORE — A fire that began on a big rig spread to a hillside near the Altamont Pass early Friday and forced an hourslong closure to one direction of a freeway that lasted into the afternoon, the California Highway Patrol said.

Westbound Interstate 580 at the Altamont Pass reopened Friday, hours after an big-rig fire led to a closure of the freeway for nearly the entire morning commute.

An 18-wheeler caught fire Friday morning on Interstate 580, igniting a vegetation fire and forcing a full closure of the freeway’s westbound lanes in Alameda County, fire officials said.