The beef slaughter house at Armour, labeled clearly on the Sanborn map, is fairly well preserved. I was surprised that it was on the top floor of the slaughterhouse building, but in retrospect, it makes sense; once the cattle are on the top floor, gravity works to bring all of the slaughtered products down into other parts of the building.
First off, I incorrectly surmised before that some sort of elevator brought the live cattle up to the killing floor. Instead, what really happened was that the cattle run rose gradually up to the top floor, as can be seen in the above historic photograph from another slaughterhouse. Likewise, if you look carefully, you can see that the annotations on the Sanborn map show that the cattle run at Armour likewise rose at a gradual rate from south to north.
There is a great little book at the Central Library in St. Louis about the slaughtering of animals at a place like Armour, and the first step would be for the cattle to be forced through a narrow passage where a man with a sledge hammer would hit them over the head to stun or kill them. See the below historic photo at another plant.
I strongly suspect that this alley at Armour, emptying right onto the killing floor, is the equivalent space at Armour.
Next, a man would grab the cow and hook its hind legs to the overhead conveyer system, that would lift it upside down for its throat to be cut, allowing the blood to spill out.
While the photograph depicts another plant, note the similarity in the appearance and form to the shot of Armour below.
Here is a blurry photo of the conveyer system at Armour, where the cattle would be drawn around the room for various slaughtering steps.
Here is a slightly older depiction of the slaughter process in Cincinnati; much of the same steps were done at Armour later.
Which brings me to the elevator system that I discovered; it was not to bring cattle or hogs up, but most likely to bring sides of beef down, into the refrigerators on the first floor.
While there was a giant freezer building across the railroad tracks that is completely demolished, there are still some coolers left on the first floor, with their Styrofoam insulated walls intact.
I assume that the conveyer brought the sides of beef straight into this room, which is lined with row after row of hangers. It was still cooler than the rest of the plant and outside on a sunny day.
So now you know how your ancestors’ beef for their 4th of July barbeques was made!
Update: Demolished in the summer of 2016.