Thanks Kevin, your educated guess is as good as anyone's.
I know it was not the saddle tree itself that caused the marks, they are far to far down on his sides, but they are exactly under the front rigging dees, which suggested to me an ill fitting or poorly made saddle that was cinched too tightly or with a cinch that was too thin or even a piece of rope used instead of a cinch.
The marks on his sides are bigger w/o his winter coat but I do not have any unfuzzy pictures, they are approx 2 inches long and 1 inch thick each when his thick winter coat does not cover them.
I never thought of a fungus causing that kind of mark or even dirt since as far as I knew those kinds of marks are caused specifically from damaged nerves and not the epidermis itself...interesting. View attachment 26308