January 4, 2016 - I did something I have been wanting to do for a long time. 
I made approximate measurements of the closest (largest) Grandfather.
     Circumference 1' above ground: 19' 6"     Diameter: 6' 3"
     Circumference 6' above ground: 15' 1"     Diameter: 4' 10"
By proportioning from photo and height of person.
     Height to first branching of trunk: Approximately 20'
     Height of tree: Approximately 70'.
What a magnificent Cottonwood tree.