Textbook example of Fasciation. Page 508 in "Diseases of Trees and Shrubs" talks about it. Could be hormonal from a variety of things. Very interesting, was the abnormal flattening all the way back to the graft union?
Yes, I believe it was a red cedar/cultivar. It was on a property that we were pruning other trees and I happened to notice this growth. I have no idea what, if any, treatments this tree has received...or the landscape in general. I almost asked her, as I thought it looked like it could have been a cause. Thanks for the feedback. You are all incredibly knowledgeable.