Some help with a 1965 Washington? Post mint?

Would someone be able to help me identify what the cause of this is? Is it mint or post-mint? The three layer appearance of the reeding is what has me curious. I mean, it's strange looking, and I have some thoughts on it, but I would like some other input. It would be appreciated.

Thanks.

 

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I always heard the reeding like this is caused by coins left in some kind of water for an extended period of time...example ... like a water fountain.. and some chlorine added to help with algae.... the copper core on clad coins is a lot softer than the outside nickel.cu layer causing the core to erode faster.... even the surface is corroded

 

Snowman's got it right. It's been exposed to an acidic environment. NOT a mint error.

 

Yes, acid. And apparently quite concentrated.

 

Have you checked the weight? If acid ate away at it, it should be underweight. I suspect this was a failed attempt at plating it, that would make it heavier. Lets have the weight...