A wildfire that started Friday in Capitol State Forest was the result of arson, a spokeswoman for the state Department of Natural Resources said Saturday.

Koshare Lomnicki, a public-information officer for the department, said the agency found evidence of “an incendiary device” near a pile of brush. She didn’t characterize what the device was but said there were not multiple fireworks at the scene.

She said the fire had grown to a dozen acres by Friday night, but firefighters had contained it by creating a perimeter around it.

“I’ve worked this area for 14 years, and I’ve never seen a fire grow that big” in Capitol Forest, she said.

The blaze started about 3 p.m. Friday in a remote section of the forest, off of a logging road about a half-mile from the Fall Creek Campground. The fire apparently began in a part of the forest that had been logged and recently had been replanted. Nearby campers weren’t directly threatened, Lomnicki said, although people were voluntarily asked to evacuate.

Crews from the McLane/Black Lake, Littlerock/Rochester and Griffin departments were among those on the scene. Two inmate crews from a nearby minimum-security correctional facility, the Cedar Creek Corrections Center in Littlerock, joined them.

Joyce Rust, a pilot from Chehalis, said she was piloting a single-engine plane over the forest a little after 3 p.m. when her passenger spotted the blaze, and she notified the tower.

“I immediately turned off to the west, slowed and descended to take a close look, being aware that with dry conditions, a fire could be serious,” she wrote in an e-mail. “We circled several times, determining that the fire was not a tended one. At that point I contacted the tower and provided GPS coordinates.”

Reached for an interview, Rust said she saw no sign of people or cars in the area.

She said she flies for a hobby and wanted to point out that aviation enthusiasts can be valuable, that they don’t just get into headline-making accidents.

“Aviation does a lot, but it’s usually quiet,” she said.

The blaze arrived as officials were fearing exceptionally high fire dangers. The National Weather Service has issued a red-flag warning until midnight tonight for Western Washington. High temperatures and low rainfall for the past two months has left grass and brush exceptionally dry.

The hot weather is set to continue today, with a forecasted high of 85. But clouds and cooler weather will return in time for the work week, with high temperatures cooling to 72 on Monday and 69 on Tuesday.

Matt Batcheldor: 360-704-6869

mbatcheldor@theolympian.com