LECHEE, Ariz. (AP) — One of three generating units at a coal-fired power plant on the Navajo Nation has closed.

The 2,250-megawatt Navajo Generating Station near Page, Arizona, is scheduled to completely shut down before the end of the year. It’s run by the Phoenix-based utility, the Salt River Project.

Utility spokesman Jeff Lane says Unit 3 went offline last week. The other two units will operate full-time until the plant runs out of coal on site.

The power plant recently received its last delivery of coal via electric train from its sole supplier, the Kayenta Mine.

The plant has been operating since the mid-1970s on land leased from the Navajo Nation.

Its owners decided to close it this year because of cheaper prices for power made from natural gas.