Nice, keen catch from Dr. Drang:
Look north and slightly east of Denver. See that big, somewhat diffuse patch of light? Here’s a zoomed-in view of that area with a few cities labeled to help you get your bearings.
Even if you didn’t know that this lit-up patch was in a generally empty area, covering western North Dakota and parts of eastern Montana and southern Saskatchewan, you could guess that it’s not a population center; despite its size, there’s no bright center to it.
The lights are from the oil shale fields spread out over the Williston Basin. It’s one thing to read about the boom in oil shale, it’s quite another to see such graphic evidence.
As a point of reference, here’s EIA map of 2011 oil shale plays in N. America.