Re NSA has a huge data center just South of Salt Lake City, not underground however.:
Thank you for clarifying that, TWW.
LAT 40.426653°
LON -111.933903°
And, the big, arc-shaped installation is clearly visible on Google Earth.
It occupies the site of what once was a little-used local airport -- which is obvious if you use GE's "Time Slider" and look at the 8/2009 overflight data. The next (6/2010) overflight shows the airport being eradicated by "site prep" work for the NSA Center...
The image resolution starts getting quite good ca 2013...
Enjoy!
TXnMA