GRAND JUNCTION, Colo. — A wildfire burning mostly federal land 18 miles north of Grand Junction was caused by a lightning strike, officials said.

The fire started Friday and has spread across over 2 square miles of Bureau of Land Management land despite low winds.

No structures are expected to be threatened, officials said, but air quality in the area has worsened. The Colorado Department of Public Health and Environment issued an air quality health advisory for northern Mesa County until Monday morning.

Dense, dried debris across the rugged terrain helped fuel the fire’s rapid growth, officials said.

Helicopters, air tankers, local ground crews and fire engines are among the resources being deployed to fight the fire.