Yellowstone Canyon!
Yellowstone canyon is amazing site in an amazing park. For me this is one of the highlights of visiting the park.
The 2 falls are viewable from both sides of the river from several locations. The canyone is also very impressive site below the falls.
Statistical data from NPS.GOV/Yell is as follows! It is roughly 20 miles long, measured from the Upper Falls to the Tower Fall area.
Depth is 800 to 1,200 ft.; width is 1,500 to 4,000 ft.
The canyon as we know it today is a very recent geologic feature. The present canyon is no more than 10,000 to 14,000 years old, although there has probably been a canyon in this location for a much longer period. I highly recommend seeing the canyon, it is a truely stunning site in a park full of stunning sites!