Iron Giant Arc - Missoula, Montana

The grassy allée of trees where I walk at lunch overlooks our company's back lot, where all manner of out-of-use parts and pieces are stashed for indeterminate time frames. Part of why I love my job is that we traffic in really big things that move - trains, ships, mining-sized earth movers - thus, the stuff out back is all BIG.  Most of them are odd and apparently specialized pieces of machinery that draw my eye with their strong lines and shapes, and also set my little grey cells to thinking what on earth they could possibly be. 

During many strolls, I wondered if today's exhibit might be an anchor for certain river terrain, or maybe it was broken off of a larger piece that completed the toothed arc to a circle that was part of a gear system. On the Iron Giant theme, perhaps it's a broken piece from the world's largest set of jacks? Finally, the wondering ceased to be amusing, so I asked the experts.

But first, I'm curious about your "maybe it's a... " fanciful ponderings, so please send a comment - we won't judge you. 
(By the way, choosing Anonymous under Comment As allows you to bypass a sign-in.)

And I'll tell you Monday what it really is.