Okay, I'll add this: Back in the 1980's, I lived outside of Parker, Arizona in a trailer park at the Sandbar resort on an Indian reservation. Outside the resort area were desert trails off into the wastelands. About two miles away, there is "an abandoned copper mine" where I explored. It was no mine, but a perfectly straight tunnel going down as a reasonable angle. No snakes, no bugs, no bats, and no smells. One day, I decided to go deeper into the tunnel. As my eyes kept adjusting, I walked about a quarter mile downward into the earth. By then, my eyes could barely see. I turned around and there in the distance was a dot of bright light, being the tunnel entrance. This tells you just how arrow straight this tunnel was. Not a copper mine. And the ceiling was consistently curved, about seven feet at it's apex. And the floor was sandy with a few small pebbles but otherwise very flat across. I now suspect that this was an air tunnel for some deep government operation. What they are doing down there is anybody's guess. In an age of cheap long lasting flashlights, were I still living in Parker, I'd be leading an expedition down there.