A long-distance bus had just broken down on Interstate 84 in Box Elder County when a lightning-ignited wildfire began sweeping over nearby fields of dry grass Friday close to the Utah-Idaho border.

“They were stuck up in that mountainous area, where there really aren’t a lot of places to go,” said Mitch Zundel, county spokesman. He said the bus appeared to be a tour bus.

County employees and nearby residents got in their cars and shuttled about 15 to 20 stranded bus passengers and their luggage out of harm’s way to the fairgrounds in Tremonton, where they were given food and water, Zundel said.

The lightning-caused fire ultimately forced crews to close I-84 for 32 miles between Tremonton and Snowville on Friday night as the flames approached the highway and threatened fields of grain crops and some ranching structures. It more than doubled in size overnight, from 7,000 acres to 15,000 acres — the equivalent of more than 11,000 football fields.

But Saturday morning, Zundel said, “Things are certainly positive.”

The interstate reopened about 4 a.m., fire officials wrote in a press statement. Crews had saved most of the wheat fields that were at risk and had dug protective barriers along the highway, Zundel said.

By Saturday evening, the fire was 45 percent contained.

“It seems like they have a pretty decent handle on it,” Zundel said.

Although I-84 is open, visibility is low because of smoke, and fire officials urge motorists to travel cautiously. The White’s Valley, Pocatello Valley and Johnson Canyon roads are closed.

The stranded bus passengers were picked up by another bus in Tremonton, Zundel said. He didn’t know their destination.