听力原文：M: It's good to see you back. How was your trip to Arizona? Did you see tile Great Valley? W: Yes, it was fantastic. Now I know why it is listed together with the Nile river as one of the great natural wonders of the world. Here, want to see the picture I took? M: Oh, what a view! It is even bigger than I had imagined. I remember reading about the Great Valley and I think it said that it was formed suddenly when an earthquake took place. W: Well, not that quickly. Look, the river has been wearing the valley floor away for ten million years. M: Then the valley is the result of soil changes. I'll bet geologists have made some interesting discoveries there. W: Not only the geologists, archaeologists have also found the bones of extinct animals in caves in the valley walls, ha a cave one hundred and forty feet 'about the river, they found driftwood that dated back as far as thirty seven thousand years. M: That means the river must have been a hundred and forty feet higher up when it carried the driftwood into the cave. W: It's very possible, but of course who knows. The Great Valley is full of mysteries. Wouldn't you like to go to Arizona some day? M: You bet I would. (23)