I noticed that as well, it’s gas flaring from O&G production. You can see similar patches south of San Antonio (the Eagle Ford shale) and in West Texas (the Permian Basin) and probably a few other spots too.

Probably fracking rigs. Where I'm from in the Marcellus shale region of Western Pennsylvania, you can see rigs on top of hills for miles when the leaves are down in winter

Edit: This map of Bakken Formation rigs correlates to their location in Western ND https://en.wikipedia.org/wiki/Bakken_Formation#/media/File:B...

When extracting or processing natural gas, it's common to burn off some of the byproduct in a process known as "flaring." It creates massive amounts of light pollution. https://en.wikipedia.org/wiki/Gas_flare

Those are the gas and oil fields of North Dakota.