Where has the woman been?

M: It’s good to see you back. How was your trip to Arizona? Did you see the Grand 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 pictures I took?
M: Oh, what a view! It’s even bigger than I had imagined. I remember reading about the Grand Canyon and I think it is said that it was formed suddenly when the earth’s 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 10 million years.
M: Then the canyon is the result of swell erosion I’ll bet geologists have made some interesting discoveries there
W: Not only the geologists, archaeologists have 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 dates back as far as 37 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 Grand Canyon is full of mystery. Wouldn’t you like to go the Arizona someday?
M: You bet I would.