What's going on with the reverse of this 1913 T1 Buffalo??

Hi all. I just came across this one on eBay and the reverse around and below the Buffalo struck me as odd. If anyone has any info as to what is causing that, please comment!
Thank you all and have a blessed day!
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It's a T1
EAC 6024
Whoops, that's what I meant. Finger slipped.
Guess this one will go down in my books as "unsolved."
Looks to me like it was struck with something on the die. Grease or rust could be the culprit but I'm certainly no expert.
Appears to have been a rusty reverse die..... Not sure what else may have caused this... Cheers, RickO
Here is a Matte Proof Type I Buffalo Nickel, which would show as much of the detail as there was in the design. You can compare it with the piece that started this thread.
Other than a small rim CUD below Black Diamond's head, there is nothing wrong with the reverse except that it appears to be a late die state. One of the reasons that Barber smoothed out the reverse fields when he re-worked the FIVE CENT wear problem was because the rough surface was hard on the dies, creating small (and sometimes larger) die cracks.
It appears that the reverse from this post has many small to medium die cracks, making this coin an example of why Barber did what he did. (Other than the fact that he loved every minute of it)
Pete