After the tunnels were created, varying amounts of TNT were set of on top of the formation to test the strength of the tunnels far beneath. Three tunnels can be seen from on top. Two of them were created by the explosives placed where the craters now are, but the third one, smaller of the three, was caused by seismic activity of the explosive charges. The sandstone failed, and the Department of Defense abandoned the project, leaving the tunnels and craters for all to speculate as to their purpose.
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