The U.S. Forest Service says a firefighter was killed when she was struck by a falling tree while working on a fire in northern Idaho.

The Nez Perce-Clearwater National Forest supervisor says the crew member was struck Sunday afternoon when one tree fell and crashed into another tree, causing it to fall in a domino effect.

The firefighter's name hasn't been released. She was working on the Steep Corner fire, which has burned about 43 acres near Orofino.

There will be a formal investigation into the death.