DALLAS - Investigators are trying to determine the cause of two fires spanning 400 acres burning in Polk County.

The initial fire started Saturday and spread to 240 acres by Sunday evening. A second fire was started by a flying ember, and at press time had grown to 160 acres.

"We're making progress. It's just slow, and we're still fighting east winds," said Jeff Forman from the Oregon Department of Forestry.

They say a black SUV was seen in the Bald Mountain area on Saturday. Anyone with information about the vehicle is asked to call the Oregon Department of Forestry's office in Dallas.

The Oregon State Police and Polk County Sheriff's Office are coordinating with the Department of Forestry on the investigation.

The fire is burning about 10 miles southwest of Dallas near Falls City. Strong easterly winds are complicating efforts to fight the fast-moving blaze that has yet to threaten any houses.

According Forman, there were seven crews of inmates and eight contract crews of firefighters working on the blaze on Sunday. They were supported by three helicopters, five fire engines, two bulldozers and eight fire tender trucks. They had encircled about 20 percent of the blaze with firelines.

Smoke from the blaze was clearly visible from Highway 99W and Interstate 5 on Sunday. Kaydra McCarger, a resident of Falls City, said that the town was not affected by the fire on Sunday and that the smoke was blowing off to the West over the Coast Range.