Sure, "broken geyser" is what I had in memory, you are probably right about it being just "volcanic activity". :P It was in the black hills, SD. I am not sure

Sure, "broken geyser" is what I had in memory, you are probably right about it being just "volcanic activity". :P It was in the black hills, SD. I am not sure of the rock formation material, but I really go the impression it was the exact same kind of rock, which is why it seemed so contradictory. Maybe it was the guides first few days on the job and they were incorrect? The cave was already formed, and the water coming into the cave caused all the formations. Could the waters have been of a different chemical formation? Seems like a reasonable explanation.