Airspace over the fire remains closed to private planes and helicopters.

BISMARCK, N.D. (AP) — A large wildfire burning in the Little Missouri National Grassland of western North Dakota is now 40 percent contained.

Nearly 100 firefighters are battling the Magpie Fire, which started Saturday in a remote area and isn't threatening any structures, people or livestock. The U.S. Forest Service says containment went from 15 percent Monday to 40 percent on Tuesday night.

The fire did scorch some grazing land. Officials also have shut down nearly one-third of the Maah Daah Hey hiking, biking and horseback riding trail, along with two campgrounds.

Airspace over the fire remains closed to private planes and helicopters.

The cause of the blaze is still being investigated.