Tom, I'll spilt a turn with you just to confuse us all even more.
When I looked at your latest pic I wanted to say Cerdidiphyllum japonicum (Katsura tree) but something is stopping me from fully committing to that answer.
Ok..here's mine, cleaning up a storm damaged limb - pic is from last winter, notice the winter flowering Rhododendron in the foreground (thats not a clue by the way). the tree is not dying back its just naturally thin for some strange reason.
I think Jeff is onto something. I know of only a few trees that develop trunk scars like that. Basswood and elm do it, but the branching looks more like white oak. Or a giant Ostrya, but I think not.
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Hahahaha! I figured it was C. glabra, but I figured it was better to be 1/2 right than 1/2 wrong, so I left the species out. What a friggin' coward.
Awesome tree. I have another if Grover will split a turn with me.