Geologists look at a land forms with different eyes, they know the language of rocks and so the can read histories written in geological features.
Looking towards the falls we can see the recent canyon history. (by recent is meant the last couple of million years)
Looking away from the falls we start heading further back into the more distant geological past.
The jointing (vertical separations) are caused from movements as the granite cooled and contracted billions of years ago deep under the earth. The joints were further enlarged in number as the granite was brought to the surface, by erosion of the layers above and experienced many eons of earthquakes and changes in stresses and pressure.
It is due to these weakened patches of joints that the river was able to carve out this canyon and continues to do so.
The water erodes the canyon via different methods. In the photo below we can see the rocks are bashed and broken by sheer brute force. Large rocks carried by flood waters bash up against jutting out potions of the side wall and break them off, leaving the concentric and feathered scars we see on the bottom right portion of the picture.
Further along we see what looks like a nice plain reasonably smooth wall of rock.
On closer inspection we see the etched scars of hundreds of potholes varying in size.
The potholes followed the joints in some places, in others they bored diagonally upstream following what must have been other weak areas in the solid rock.
Further down we see much longer pothole scars.
Long ones following the cracks and long vertical ones.
Some almost horizontal ones.
From these scars it is easy for a geologist to read that most of the initial removal of material was along this wall, to form the first channel in this area and was due to potholes boring away at the solid rock and a few joints.
The mechanical removal (bashing) came later once the initial water channel was formed.
If you missed what potholes are, I cover them in the previous post of this series
Other posts in this series
Augrabies - The hidden river
Augrabies - The Falls and Floods
Augrabies: a "heart of stone" for valentines day.