Walt Brown: "Release of Grand Lake’s vast waters first eroded hundreds of meters of relatively soft Mesozoic sediments off northern Arizona. Once surface erosion was completed, downcutting through the harder Kaibab limestone began."
Nonsense. There is no evidence for this except that the Mz rocks happen to not be present at the GC. However, if there were such erosion of the Mz rocks, there should be some kind of channeling and sheet runoff features all over the Kaibab Uplift. There aren't.
Walt: "As erosion cut deeper beneath the water table, more water, under greater pressure, was released from the water-saturated sediments flanking the canyon."
Fortunately, for us, Walt does not practice hydrogeology. Ground water cannot be regionally under excessive pressure when exposed to surface waters. Also, he has no idea what releasing such pressure would do or the evidence it would leave. This only makes the cliffs of the GC MORE unlikely.
Walt: "This escaping water cut dozens of side canyons entering the Grand Canyonlarge canyons previously unexplained because they have no significant surface flow entering them. Subsurface flow and landslides were extreme."
There is no evidence of such jetting of water from the canyon walls. The side canyons form normal dendritic patterns, sometimes controled by preexisting brittle-rock structue. I'm not sure what he means by 'subsurface flow', but extreme landslides may be actually correct. We know that this is the modern method of forming the canyon and probably the side canyons: landslide dams and breeching of dams.
Walt: "The weight of material removed from northern Arizona produced isostatic uplifts that account for the uplift of the Kaibab Plateau. This produced much faulting and volcanism, the barbed canyons, and layered strata that dip down and away from Marble Canyon and Grand Canyon."
It is true that erosion results in isostatic uplift. However, I would love to see Walt's actual calculations on this.
L: Actually, it is not even MY knowledge of the subject; it is Walt Brown's...I know pretty much nothing about geology.
Well, then, you have something in common with Walt...