The two wildfires that burned south of Finley on Friday night had suspicious origins, officials said.
One of the fires charred 500 acres of wildland along Owens Road about one mile south of Highway 397, said Jack Coats, assistant chief and fire investigator for Benton County Fire District 1.
The other fire only burned about 5 acres near Meals Road and was quickly put out, he said.
The fires were reported within an hour of each other, the first about 8 p.m. Friday.
No structures were threatened and nobody was injured in the fire, Coats said.
The about 40 firefighters from Kennewick, Richland, West Richland and Benton City contained the larger fire around 11:30 p.m.
Firefighters returned to the Owens Road fire this morning to "check on some hot spots," Coats said. They declared the fire out at noon Saturday.
The proximity of the two fires to each other and their distance from any power lines or other possible fire starters roused investigators' suspicion, Coats said.
"There's nothing out there that could start a fire naturally," he said. "Nothing that could start by it by itself."
Investigators have ruled out camp fires or field burns as a cause and are treating both fires as "suspicious in nature," Coats said.
"We think somebody was running around setting fires," he said.