Three blistering fires are blazing through Wyoming’s scenic Powder River Basin, but firefighters aren’t paying any attention. Other than a faint hint of acrid odors and a single ribbon of smoke rising from a tiny crack beyond the nearby Tongue River, a long look across the region’s serene grassland shows no sign of trouble.

That’s what makes the three infernos, and the toxins they spew, so sinister. Their flames are concealed deep underground, in coal seams and oxygen-rich fissures, which makes containment near impossible. Shielded from fire hoses and aerial assaults, the flames are chewing through coal seams 20 feet thick, spanning 22 acres. They’re also belching greenhouse gases and contaminants, contributing to an out-of-sight, out-of-mind environmental hazard that extends far beyond Wyoming’s borders. ‘Every coal basin in the world has fires sending up organic compounds that are not good for you,’ says Mark Engle, a geologist with the U.S. Geological Survey who studies the Powder River Basin, ‘but unless you live close to them you probably never see them.’

A surprising number of us live close to them. According to a review by the Department of Interior’s Office of Surface Mining Enforcement and Reclamation, more than 100 fires are burning […]