Growing numbers of geologists now believe that Marble Canyon and the Inner Gorge may be no more than 700,000 years old -- veritable infants on the geologic time scale, and much younger than the earlier 3-million- to 5-million-year-old estimates. Some scientists now believe that a third of the canyon's depth may have been cut in the blink of a geologic eye -- perhaps during the past 600,000 to 700,000 years.

As time goes on, catastrophism is becoming more, and more, and more accepted...

"Large sustained floods can cause rapid downcutting in bedrock"