What is it?

[DPatton]

My Dad would have called it Pi double S Elm.

I agree that at first I thought the bark more closely resembled elm than the typical walnut in my area. But the branches don't look like our typical elm either. I have a neighbor who says it's some type of Chestnut but I don't know the first DanG thing about Chestnut varieties. 
 This tree and all the other trees I harvested logs from on this site were all already pushed down with earthmoving equipment before I got there. It has surprised me how identifying dormant trees laying on the ground versus still standing dormant trees becomes much more of a challenge, at least it does for this greenhorn anyway. 
I also have a guy who "swears its hickory" ;D ;D ;D

[SwampDonkey]

The exposed wood looks like walnut as does some of the buds. But some of that brush is like maple or ash. From what I can tell there is piles of brush from more than one tree. If Danny or fellow dendro master were standing over that log I'm sure it would be solved in short order. ;) :D

[WDH]

The first branch pic and the second branch pic look like different species. 

[TKehl]

Agreed.  Makes me wonder if it was a young black walnut growing up next to an Elm.

[DPatton]

The exposed wood looks like walnut as does some of the buds. But some of that brush is like maple or ash. From what I can tell there is piles of brush from more than one tree. If Danny or fellow dendro master were standing over that log I'm sure it would be solved in short order. ;) :D

SwampDonkey 
You are correct as the first pic showing the main stem bark and the last pic showing the end cut of the main stem do have maple limbs with buds in the background. However the 2 limb pics I provided are both from the tree in question. In fact if you look close enough you will see that the second limb pic showing the buds is just a closeup of limbs in the first photo. The first photo has Danny's "Red Herring" (opposite branching) limb in the upper left too.    

[KEC]

The last photo, I think, may be an Oriental Elm/Chinese Elm. I cut one for a guy many years ago and I'm not sure if this is the same.