Need help with tree ID
I've lived in my 20 acre Eastern deciduous woodlot for 3+ decades, and in that time, have been able to ID all the trees - except one. I've always thought it was an Elm, but its bark doesn't match any Elm that I've found in books or online.
My woodlot is 1/2 "hills & hollers", and 1/2 rich creek bottom. These trees grow only in the bottom, not a single one can be found on the hills. The leaves are very similar to the Eastern hophornbeam and the American hornbeam, but they're neither. TIA for any help.
This is the largest one:
This one is fairly young, with the top of my walking stick for scale:
The leaves on the left are the mystery tree, American hornbeam in the center, and Eastern hophornbeam on the right: