From the Niagara Falls Review:
Fear of heights is not an option for crew members scaling the rocks along the Great Gorge wall.
The Niagara Parks Commission began its annual gorge cleanup this week, as crews scaled the rocks and removed any potentially dangerous loose pieces.
Over time, particularly in the winter months, water gets trapped in the crevasses of the gorge’s rock face and continually freezes and thaws. This creates unstable pieces of rock that must be removed before tourists are able to journey behind and down towards the falls.
There is a small picture in the Review of them scaling the wall. I’ll try to walk by there and take some pictures myself.