(Note: this post was made mistakenly as a page, and didn’t go up at first. Now it’s here. Thanks to commenters for the help.)
Turns out the one above, a giant W in the Arizona landscape, is the Black Mesa Mine, and it has been mothballed since 2005 when the destination of its coal (via an unusual route), the Mojave power plant, was shut down. The Kayenta Mine is still running, as are the other mines I saw off to the east around the Four Corners areas.