Using data from the EIA, this map shows only those powerplants in the US that have both coal and natural gas generators. With the influx of natural gas on the market due to increases shale gas deposits discoveries and improvements in extraction techniques, mainly in the way of fracking, coal has become a more expensive and less desirable fuel. Because of this, many powerplants have been shifting generation from older, more costly coal generators to newer, more efficient, and environmentally friendly natural gas ones.
This map shows the total energy output of those powerplants, and the ratio of coal and natural gas production over the past 8 years.