Probably carbon monoxide
The earth will belch deadly hydrogen sulfide in places and I think NM is one of them.
You could be right, but after reading you comment I was struck by the following. After looking into the numbers, I learned that;
In America an average of 5,000 people dies every year from carbon monoxide every year. Yet 48 states in America have laws placed by politicians the dwellings must have at least one and in some states 2 or three carbon monoxide detectors.
Now consider the amount of detectors sold every year in America by law. Maybe we need Musk to start looking into the scam of politicians getting rich from businesses getting unneeded laws passed in America so they can sell products no one wants.