The U.S. Silver Fox Farms had three major locations, Spokane (WA), Minneapolis (MN), and Shasta Springs (CA). This is a photo of the site of the Minneapolis farm, actually located outside the city in St. Louis Park.
This panopticon (see the green arrow) was only partially built, or perhaps partly demolished, so it looks like a half-circle, with pens radiating outward. On this image, you can clearly see the watchtower in the middle.
A local history of the farm is given here.
Panoptifox 