OK, so it sounds like some place near Reveille. Again, I don't want to
play 20 questions. If there is a spot you think is worth investigating,
please name the spot and I'll check it out.

Note that there are many applications for VLF signals to be generated
beneath the ground. One is for detection loops. Another is to guide
vehicles above ground, generally for robotic use. Sandia has a paper on
such an application.  I can't locate the paper with the VLF frequency,
but I believe it was used in this project:
http://www.sandia.gov/isrc/perimeterdetection.html
The idea was to have the robot follow the buried wire radiating VLF.