Coal has been the majority or near the majority of power generation until very recently. And it's only as low as it is now because natural gas got cheaper. https://en.wikipedia.org/wiki/Coal_power_in_the_United_State...

I have no idea how many facilities this is, but coal plants can also be retooled for gas: https://www.transalta.com/about-us/coal-to-gas/

One of my favorite graphics -- although it also includes petroleum: https://flowcharts.llnl.gov/content/assets/docs/2018_United-...