The leaves and deep grooved bark makes me think it's Black Locust. Any sign of thorns in amongst the leaves where the branches grow out from other branches? If BL, that's good firewood laying right there.
I think that round nut clinches it for black walnut. Butternut is egg shaped (they're also rare and endangered). Not to mention the bark is a dead ringer for the BW I have around here. Black locust has round leaflets, and it's in full bloom around here at the moment.
Well now I looked at the pic again and it looks like there is an egg shaped nut underneath the round one. So I guess I'll just return my "superior knowledge" to my backside from whence it came... I revise my guess to "firewood".
It's gotta be butternut or pignut. I have forgot to take a pic, but I have Black Walnut within 50 yards of this tree...not the same. My black walnut bark looks identical to the one I posted above, not nearly as widely furrowed and gnarly as this tree is. That is indeed what it is....er...will be. Hope to get my buddy down next weekend to saw up and haul off. He's not too picky...it's freeirewood. I have been to tree ID classes 3 or 4 times over the years and still get tripped up easily. People that know me will take a picture of wood and show me and expect me to absolutely know what I'm looking at...not that easy!
I have literally about 2,000 Black Walnut trees on my place and the bark variance is all over the place. Some of it looks like your tree in question, others look like the earlier pictures you posted that are sort of blocky and chunky, some have deep "X" pattern furrows...but I know for a fact they're Black Walnut...I've mowed over, roller skated on, etc. plenty of walnuts to stay good and pizzed at these trees when they drop their nuts. One thing that they all seem to have in common is a ton of leaves on the branch tips...like 14+ leaflets. Your pics show nuts that look somewhat elongated though and I have absolutely no experience with butternut so I can't help you there other than the bark on BW is all over the place sometimes.
The Walnuts around my place all look mostly similar as far as bark. The tree in question is an oddity in my locality. Not to say there aren't more, but much less common than b walnut I have. 100% in agreeance with you on bark variances though. There is for sure not a one and only type for any given tree in every locality. I'm sure the site it grows upon along with other factors determines the characteristics of a particular tree. I have decided that this tree is indeed a Butternut. Mast and leaf structure match up along with the differing bark from known local black walnuts have led me to this conclusion.
Seems that when the bark is something that throws you off, look to leaves and fruit/nuts. Depends on that. But even fruits get hard to ID since they get to be in different stages of growth. The in between period is where it gets tough. Morphology and all that can be tricky for sure. Same for even someone who's lived in the area for their life!
