I've spent many hours looking over this pic as it was Andrew Carnegie's steel mill. When zooming in on it one can see many things in good detail like a horse and buggy and a street car. Yes, the Pittsburgh area had street cars. This site also was where General Braddock made his crossing of the Mon River before his great defeat. If one looks far left on the same side of the river at the base of the hill you can see a town there and that town is no longer there and was Port Perry.
Jeff, No, that is just dirt in an odd shape believe it or not. That area was bull dozed for a proposed street at the time. The homes in that direction is the town of Braddock and is looking westward. The general direction the pic was taken was just southwest.
If one were to look at Google Earth one can see where Port Perry used to be and is now all railroad.