hmmmm what's on that same horse's belly? looks like the top of a picket fence. Trying to imagine that coin's back...is it a clash die of "trust"? wish i had the overlay image of that :O
I found record of 2 others similar having already been found. Did a start page image check for "nevada 2006 quarter mint proof". They did not display the chest anomaly nor did the L/R hoof/pastern area of the middle horse look jacked as this one does. I have one far less pronounced and shows problems just between the hind legs of the uppermost horse.
@Ordinary Fool wow cool then if you've seen this before it may be something...i hope we can get 2-3 to concur or having seen similar (i'm a newbie, i don't count as a head LOL) if you see that picket fence on the horse's (horse to the right, in the back) belly and chest....the "Picket fence" shows in front of the horse too...i looked at images of other "normal"Nevada coins and i didn't see that in them.
go to startpage and perform the image search as I laid out. It is something. An error and at least 3 others exist, 2 I just found published in 2016 and the one I have. None appear identical and yours appears to be the most epic so far. My guess is that die didn't churn out too many before being corrected. Great find.
Those are not the result of a clash, the area in question would be raised and not incuse for this to happen.
Do you agree it is some sort of error likely attributable to a die on its last legs? Could the OP post some detail pix of the middle horse's rear legs?
It is peculiar, what do you think it is? From the picture, I can't tell 100% if it is raised or incuse. Maybe I'm looking at it on too large or too small displays. Do you have a link to a good reference where one searching can readily pull up LARGE mint proof images of various denomination coins? Or various links to various denominations? I'm sure such must exist and not just the small photographs I've found on the mint's site and other places. Thanks.
I know you stated that in post two, I don't think that the area, on the horses belly can be attributed to the die chip.
Added outline to the rear thigh and neck of the middle horse. All in red and thicker now. Let's see if Comfortably Numb posts more images