I had spent a lot of summers visiting relatives in Western Pennsylvania in the 1960's-1970's. Staying in nearby Wilmerding, Pitcairn Yard was close-by and always interested me.
I happened to find most of these great images from the University of Pittsburgh's Historic Pittsburgh Library system. Some of the images they have listed seem to have dates that are incorrect judging by the older style headlights, but they are still to be commended for posting these beautiful images.
This description was on their website:
Finished in 1892, the Pitcairn Railroad yard included classification and receiving yards, transfer and assembly tracks, two roundhouses, repair shops, machine shops, and its own lumber yard and power plant. Cabinet shops, upholstery shops and paint shops were also set up to repair and refurbish passenger cars.
Tom