BOULDER COUNTY, Colo. (KDVR) — A fire that has been burning for more than a century in Boulder County has been extinguished.  Underneath the present-day Marshall Mesa trailhead lies one of 14,000 abandoned mines across Colorado. Mining activity ceased at the site in the early 1900’s, but the coal still left in the ground has been burning ever since.  Previous coverage: Work begins to mitigate decades-old underground fire in Boulder County “There’s records from several coal mines, including this one, that the fires were burning while they were being mined,” said Tara Tafi, senior project manager with the Colorado Division of Reclamation, Mining and Safety.  The area was eventually developed as part of the Boulder County Parks and Open Space. According to Tafi, many visitors likely did not know about the fire burning beneath their feet.  “No, there wasn’t a lot of surface expression,” she said. "You didn’t smell it on site." However, the Marshall site raised questions following the Marshall Fire in 2021, which destroyed more than one thousand homes. The coal seam fire has never been proven as a contributing cause to the Marshall Fire.  Tafi did say, however, that underground coal fires have caused Colorado wildfires, primarily on the Western Slope, in the past. In 2022, Colorado received a significant amount of money from the Bipartisan Infrastructure Deal to begin tackling its ongoing problems with underground coal fires. There are about 40 known sites across the state.  How Los Angeles wildfires compare to the Marshall Fire “They’re not all going to be able to be extinguished,” Tafi said. "Unfortunately, the geology just doesn’t lend itself to us being able to do a full excavation extinguishment on every site."  The Marshall site is uniquely accessible.  “One of the reasons that we’re here is that we actually saw the opportunity to put this one out,” Tafi said.  Excavation began in November 2024. The site is 12 acres and required heavy machinery to dig down to a depth of about 30 feet. The layer of coal was broken up and mixed with rock and soil that had been lying on top of it.  “For a hundred years this is the area that has been problematic and we have now excavated it to the point where there is no remaining coal resource underground in this area,” Tafi said.  With coal broken up into smaller chunks and blended with other ground material, any pieces of coal that could still catch fire would quickly burn itself. In the final few weeks of the project, crews are grading the landscape to fill in the holes they dug.  “We’ll re-contour it to resemble the surrounding undisturbed topography and make it as park-like as we can,” project manager Jeremy Reinieke said.  He says he hopes people who live and recreate in the area can feel optimistic about the future of the site when it comes to fire mitigation.  “A lot of them are really glad to see somebody out here doing something that’s visible and concrete and they’re happy to know that at least one concern can be checked off the list,” Reinieke said.  Once the DRMS team finishes its work in February, the site will be turned over to Boulder County to begin rebuilding the infrastructure for the trailhead.  DRMS is already planning two more projects that will commence in 2025 to extinguish underground coal fires in Fremont County and Craig.