Highway 2 northeast of Seattle remains closed to all except local residents between the towns of Index and Skykomish as firefighters battle the Bolt Creek fire.

The blaze had burned an estimated 15.9 square miles by Sunday night and has dropped rocks, trees and other debris onto the highway, according to the Northwest Interagency Coordination Center, The Seattle Times reported.

A spokesperson for the firefighting effort, Andy Nesmith, says crews are focused mainly on the southern part of the fire closest to the towns and highway and are allowing the northern portion to burn.

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The north portion of the fire — which is creeping through the steep and craggy Wild Sky Wilderness — isn’t threatening roads, structures or people, Nesmith said, and crews have little access to the area.

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The goal is prevent future spread of the fire to the west and east. As of Monday morning, 79% of that work was complete.

The fire started Sept. 10 during hot, dry and windy conditions, causing hikers and residents to quickly evacuate.