BOISE — More than 800 wildland firefighters and support staff are battling a blaze in east-central Idaho that officials say is threatening homes, an important north-south corridor, energy infrastructure, recreation opportunities and the municipal watershed for the town of Salmon.

The Moose Fire on Tuesday grew to nearly 60 square miles burning grass, timber understory and dead and down material in the Salmon-Challis National Forest. It’s only 10 percent contained.

Firefighters are protecting structures in several areas as well as the U.S. Highway 93 corridor. Two helicopter pilots fighting the fire died last week when their CH-47D Series “Chinook” crashed in the Salmon River. Plans call for removing the helicopter from the river with a large crane.

The cause of the fire that started July 17 is undetermined. High temperatures and very dry relative humidity are hampering efforts to control the blaze. Smoke has also been a problem. The sky above Challis has been hazy for a couple of days.

Firefighting plans call for trying to check the fire along U.S. 93 and do preparation work to protect structures in the fire’s path. Firefighters are also worried about long-range spotting where embers can drift far from the fire and start new spot fires.