IMNAHA, Ore. (AP) — About 300 firefighters assisted by air tankers and water-dropping helicopters were building containment lines Sunday to combat a growing wildfire in remote eastern Oregon that forced has evacuations of campers, authorities said.

The Double Creek fire near the community of Imnaha in Hells Canyon Recreation Area grew to about 37 square miles (96 square kilometers), fed by gusty winds on Saturday, according to the National Interagency Fire Center.

The fire prompted evacuations by campers from Imnaha south to Pallette Ranch, the Wallowa County Sheriff’s Office said. The fire, burning on conifer timber stands and grass and shrubs, was detected on Tuesday and started by lightning.

Gov. Kate Brown on Saturday issued a declaration allowing the state fire marshal to take command and send other agency resources to help local firefighters. Crews were focusing Sunday on building containment lines at the fire’s southern edge and along the Inmaha River corridor.

Firefighters were monitoring two other lightning-caused fires in the nearby Eagle Cap Wilderness. The Nebo Fire has charred 11 square miles (28 square kilometers) of rugged terrain, while the Sturgill Fire had grown to 13 square miles (34 square kilometers). Crews were allowing the two fires to feed on dry fuels while protecting structures.