The Mine Safety and Health Administration produced a report [1] with an inconclusive "Possible Causes" section. One thing I noticed there is that "the plotted

The Mine Safety and Health Administration produced a report [1] with an inconclusive "Possible Causes" section. One thing I noticed there is that "the plotted location of the drill hole fell just within a mined-out section." I wonder if the drillers were using a map showing only the active galleries, though I would imagine that would have been mentioned if it came to light. There are detailed maps and drawings of the mine works in this report. Also, there is a diagram [2] to be found in several places, apparently from Keller & Blodgett "Natural Hazards" (Prentice Hall.) [1] https://books.google.com/books?id=EbjC-q99VHAC https://books.google.com/books?id=EbjC-q99VHAC [2] http://www.thelivingmoon.com/47john_lear/04images/Sink_holes/peigneur3.jpg http://www.thelivingmoon.com/47john_lear/04images/Sink_holes...