The article didn't bring this out well, and I haven't read the book in quesion. But I think the problem with river cones is that none of them are as big as they should be if the earth is millions of years old.
It does raise some interesting questions. Why did the Colorado carve such a huge canyon, but the Amazon and the Nile haven't?
Once rivers that flow over rock, like the Colorado, cut a groove, they naturally stay in it. Eventually they dig down towards sea level. How deep the canyon is depends on water flow, rock hardness and how old the river is.
Until man started to force themn to stay within their banks, rivers through soft soil moved around, creating and then cutting off horseshoe bends, thus the current course of the river is never more than a few hundred years old.
The mouths of the rivers also move around.
The Mississippi moved back and forth over a 100 mile stretch of coast, until we stopped it. In the last 300 years, the mouth has moved 50 miles South out past what was the coast.
So9