Not really in the plains, but there is a fat old oak in Schwartzkopf Park in Marysville:
It's located down in a small floodplane on the banks of Mill Creek.
H: 79.5'
cbh: 16' 1"
spread: ~ 70' (36', 40', 30')
Both the height and the spread were a challenge to measure. The tree is relatively flat topped, and I had to go fishing for nested twigs. I found two that were just shy of 80'. There are likely slightly higher ones. The tree is growing right on the edge of Mill Creek, and leaning over it. I took 3 'spoke' measurements CCW around the trunk on dry land. 70' is probably the minimum, while the max is over water, along the same axis as the tree's lean:
Picture of my Dad in front of the trunk:
The tree is still healing the scar of recent lightening strike:
Given the irregularity of the crown it was probably hit significantly once before, a loooong time ago.
Another curiosity is the leaf differences on different pendulous branches, only 10' or so appart:
Classic Bur Oak leaves:
vs. an almost White Oak appearance