There is always a conflict between artistic, random and speed when you craft something like these canyons. They are chaotic and seemingly random so running through and rapidly cutting the raw foundations edges back or just using a smoothing tool should wrap it all up in minutes. If you spend a little time looking at pictures of the real world geo formations you are trying to emulate, you will see repeating features due to the nature of the rock type and how it weathers. Water being the strongest eroder and sculptor.
Ask your self what will water do to this, then run through with a cutting tool and rapidly erode the walls and pull water cuts. Spending too much time will cause you to get lost in artistic dead ends and blow away more material than you intended. Faster but not careless ends up with a balance that looks sort of like real world chaotic. Since this is all about the illusions you are limited to by the size of the polygons.