ASHTON, Idaho (KIFI) — The Caribou-Targhee National Forest has issued an immediate emergency closure for a section of the Railroad Grade Trail following a fire inside the historic Bear Gulch railroad tunnel. The closure impacts the trail from the Bear Gulch trailhead north to the junction with Forest Service Road 154 (Warm River Springs Road). While winter conditions are aiding suppression, the Forest Service says the historic tunnel itself presents a unique challenge. USFSCaribouTarghee"A lack of structural stability within the Bear Gulch Railroad tunnel has prevented firefighters from accessing internal heat sources that continue to produce smoke that may be visible in the Bear Gulch Area," stated the Forest Service in a release. The Forest Service says fire crews will remain on-site to monitor the piles and ensure all combustible materials are extinguished before the spring snowmelt.