Plummer Jct

Plummer Jct is the STMA's primary connection to the outside world. Here, the Union Pacific's Plummer branch connects to the STMA, where empty boxcars and centerbeams head back to St Maries, and in the spring and summer, tank cars of road binder also head to St Maries to be spread onto dirt roads to keep dust down.
LAYOUT
The actual layout of Plummer is similar to any peninsula-like model railroad set-up. The Union Pacific comes along one side of a hill, while the STMA comes around the other, and the two lines join, while a wye formed by two routes off the round connection allow for interchange between the two roads. Union Pacific also switches a few customers in Plummer (including at least one lumber mill), but as the focus here is the STMA, I'll go back at a later date and explore these industries.
I will hopefully have measurements for these tracks at some point, but here's a Bing maps look: http://binged.it/L6c0Xf
Operation
There are several different ways to interchange cars that I have seen on youtube. In one video, the STMA Geeps are waiting for the Union Pacific's train, and when it arrives, the power cuts off and pulls down the UP's leg, then the STMA backs up to the cars, pulls them, and the backs down its own wye leg, before leaving for St Maries (I'm not sure why they back down the leg, since they're pulling their own cars away from the UP it seems). In another video, the STMA pulls in, drops its cars on what I would assume to be its spur legs (although in theory the cars could be dropped on either the UP leg or the shared tail). They then back around and wait for the UP train, and then, as before, the UP drops its cars, pulls forward, and the Geeps back up to the train and haul it around the curve.
Found this picture on Google, so it seems the UP will come around the curve and spot its cars on the wye leg and pick up its own cars as well. http://railroadheritage.org/ImageStorage/Img--00005077.jpg