Thanks all for the confirmation. I really wanted it to be a railcar coupler, but wasn't quite seeing how it could securely connect to the other piece and so thought it might have been used somewhere else. Too many times I've wanted something I've found to be X, convinced myself it was, and then been disappointed to find out it was actually Y.
So this area I knew had a town site about a hundred years ago. I was walking through the woods in the general vicinity of where I thought it might be. I stopped and looked down and just beside me was a stack of old barrel hoops leaning against a tree, which was pretty encouraging. I was meeting a few other people on a hiking/fishing trip, but I found the spot again a few days later. From where I was standing, I looked around, and all of a sudden, it dawned on me that where I was standing was an old railroad grade, and I was looking at the convergence of two old railroad grades. While this isn't a great picture, here I'm standing where the grades came together. One grade veers slightly to the left and has the fallen tree across it in the distance; the other veers ever so slightly to the right and pretty much goes through the middle of the picture, between the two standing trees.
I walked out the right grade, which went through a little cut in the land (further confirming I was on a grade. This brought me out to the banks of a little stream; over the years, it has had many avulsions and jumped channel a lot in this area, but it also became clear where the grade originally went. Walking slightly parallel to the current stream course, and slightly upstream, I looked down into this puddle on the left side of the grade. And the coupler was sitting right there.
I wasn't exactly sure what to do. I already had a full 40 pound pack on (yes, I was way overpacked for a summer trip, but I was carrying fishing gear and a few empty bottles). So I hauled the coupler back to my site, which was just downstream. I found it was hollow and washed out the years of mud and corrosion that had accumulated inside. I thought about walking out, emptying my pack and returning to retrieve the coupler, but didn't want to add another four miles of hiking to my weekend. I thought of stashing it and returning at a later day, perhaps on a day-hike. I thought of putting it in my bear bag and carrying it out like a grocery bag, but it was too heavy. So I ended up putting it my bear bag (to keep my pack clean), put it in the bottom of my pack, repacked everything else, and figured I would see how far I made it. The first hundred yards were fine and then I confirmed that my pack really was too big in the waist belt, as fully tightened, the belt wasn't transferring the weight to my hips, but the bulk of my weight was on my shoulders. I've since upgraded to a better fitting pack and have experienced a lot less soreness because of that. Anyway, it was also an extremely hot day, so I would walk a few hundred yards, stop and brace myself on my trekking poles, and then plod on. I was very much afraid that my pack would rip; it was really designed to carry about 35 pounds, but to GoLite's credit, the pack held together. My few hundred yards at a time eventually shrunk to a few hundred feet at a time, but after a two mile walk out, I guess I held together too, although I was dead tired, dehydrated, and definitely sore.
If the woods could talk, I would love to know how a coupler ended up chucked into a stream bed, over a hundred years ago.