Where has the woman been?

M: It’s good to see you back. How was your trip to Arizona? Did you see the Great Canyon?
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 Canyon and I think it said that it was formed suddenly when the earth crust split open during an earthquake.
W: Well, not that quickly. Look, here is the picture of the Colorado river. See way down at the bottom of the canyon, that river and its tributaries have been wearing the canyon floor away for ten million years.
M: Then the canyon is the result of soil erosion. 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 canyon walls. In a cave one hundred and forty feet above 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 drift wood into the cave.
W: It’s very possible, but of course who knows. The Great Canyon is full of mysteries. Wouldn’t you like to go to Arizona some day?
M: You bet I would.