This photo from the back cover of the Johnstown Flood July 20, 1977 Memorial Edition. I don't know what part of Johnstown this was taken, but photo clearly demonstrates the destructive power of water and how it gouged out part of this street.
The first one is one of the most iconic photos of the 1889 Flood. It's the Shultz House with a tree stuck through it on the corner of Main and Union Streets. The one below it is the Stone Railroad Bridge with debris around it.