In late December, seven dead cattle were found near an oil field in the Cimarron National Grassland, Kansas, and authorities believe that cows inhaled something toxic, prompting them to deny public access to the 2,500-acre Cimarron National Grassland until at least May.
Six of the cattle were discovered together in a low-lying area, while a seventh was found a short distance away, with local veterinarians identifying the ingestion or inhalation of something toxic leading to pulmonary edema or fluid in the lungs as a possible cause, though the cause of death has not been officially declared.
More specifically, they suspect the cattle may have inhaled hydrogen sulfide—a toxic gas that can be released in the oil and gas drilling process. They haven't pinpointed the cause officially, but it was enough to implement an emergency order to halt public access to the area for a prolonged period.
Comment: As well as hydrogen sulfide being released in the oil and gas drilling process, natural outgassing of toxic gases can also occur.
Other possible cases of outgassing around the United States in recent times include: