This is what the demise of the coal era looks like. The chart below from the Energy Information Administration (always a source of superb graphics, BTW), looks at both the age of the U.S. "fleet" of electric power generators and how much energy they produce. (Click to enlarge.) Most notably, coal-fired power plants, big in the 1970s and '80s, petered out almost entirely in the '90s.
As Brad Plumer notes,
Since the early 1990s, utilities have mostly stopped building coal and nuclear plants, thanks to a combination of costs, regulation and pressure from outside groups. The Sierra Club, in particular, has done a lot of work to prevent utilities from building new coal-fired plants.
Yay for us! Meanwhile, starting around the turn of the millennium, nearly all new construction and power provision has come from natural gas and wind. Of course, as my colleague Reed McManus points out, generating all that energy from natural gas is not unalloyed good news. But coal is clearly a fuel whose time has passed.