The following story shows extreme levels of CO (carbon monoxide)
on the West Coast, and especially in the Central Valley of California.
CO has been linked to earthquakes, but the levels themselves are
a hazard. These are not man-made, but seepage from earthquake
faults such as the San Andreas.
Ground water depletion has also been linked to earthquakes, and
California farmers have been depleting groundwater for decades.
So this is injury upon injury.
The story has a link where you can monitor an up-to-date map.
Be prepared.
Carbon Monoxide Spikes to 27,000+ Where "Usual" is only around 150 on West Coast - May Signal Coming MASSIVE Earthquake