Pittsburgh, PA: Pennsy Roundhouses destroyed during riot by striking workers in July 1877.

Roundhouses: (Satellite)

These roundhouses and the railyard shown below in a topo map supported the Pittsburgh Depot.

Jackson-Township historical preservation posted
Burnt out Pennsylvania Roundhouse at Liberty Avenue and the 28th Street Bridge in Pittsburgh during the Railroad Strike and Riots of July 21-22, 1877. In July, after refusing to negotiate with striking workers in Pittsburgh, the Pennsylvania Railroad brought in militia from Philadelphia to end the walkout. When the Philadelphia militia fired into a crowd killing 20, enraged Pittsburghers attacked the troops and burned the rail yards. By the time the rioting ended, some 40 people had died, one hundred locomotives and 1,000 rail cars had been destroyed and 39 railroad buildings were burnt to the ground.
(Photo from https://www.facebook.com/OddPittsburgh/) 
[This was the one just west of 28th Street.]

John Gombita commented on the above post

John Gombita commented on the above post
The previous map is from 1872, This map is from 1882. Many properties and railroad structures were not rebuilt.

Jackson-Township historical preservation posted

Destroyed locomotives and railroad carsat the burnt out Pennsylvania Roundhouse at Liberty Avenue and the 28th Street Bridge in Pittsburgh during the Railroad Strike and Riots of July 21-22, 1877. In July, after refusing to negotiate with striking workers in Pittsburgh, the Pennsylvania Railroad brought in militia from Philadelphia to end the walkout. When the Philadelphia militia fired into a crowd killing 20, enraged Pittsburghers attacked the troops and burned the rail yards. By the time the rioting ended, some 40 people had died, one hundred locomotives and 1,000 rail cars had been destroyed and 39 railroad buildings were burnt to the ground. 

(Photo from https://www.facebook.com/OddPittsburgh/)

James Louis: https://www.britannica.com/topic/Great-Railroad-Strike-of-1877

[This is the one just east of 26th Street because we can see the other one in the right background.]

The roundhouses were part of a railyard that served the Pittsburgh Depot that was on the west end of the yard. The railyard also helped serve the many industries that we see on the Sanborn maps.

1951/51 Pittsburgh East Quad @ 24,000

Digitally Zoomed

Both transfer tables are depicted rather weirdly. The western one has as many tracks feeding it as there are tracks in the building. The eastern one doesn't have any tracks feeding it.

Even without a fire, these backshops would probably have been replaced with shops in railyards in towns with cheaper land. For example, Altoona.

Digitally zoomed from 1872 map above