In the desert near Arizona’s border with Utah on the Navajo Nation, a massive solar array built in 2017 now provides power for around 18,000 Navajo homes. Nearby, construction will begin later this year on a second solar plant. And on another corner of Navajo land, the largest coal plant west of the Mississippi River is preparing to close 25 years ahead of schedule, despite some last-minute attempts to save it.

“Those two [solar] plants really are the beginning of an economic transition,” says Amanda Ormond, managing director of the Western Grid Group, an organization that promotes clean energy.

The coal plant, called the Navajo Generating Station, was built in the 1970s to provide power to growing populations in Southern California, Arizona, and Nevada. A nearby coal mine supplies the power plant with coal. As recently as 2014, the coal plant wasn’t expected to close until 2044–a date negotiated with the EPA to reduce air pollution. But reduced demand for coal, driven both by economics and climate action, means that the plant is scheduled to close in 2019 instead. The coal mine, run by Peabody Energy, will be forced to follow.