Volcano sculpture

This is an image of a piece of sculpture I did during my elementary school years in summer school for special people like myself (especially since I'm autistic).  Of course, the material I used was Play-Do, which is why it has small cracks in several places (you need look close.  Unfortunately, the sculpture is not around anymore on account that my mom force me to discard, something I felt reluctant to do.  That is why I decided to take several photographs of it years ago before discarding it.  If you observe, there's a brown stain on the edge of the it, yet, I have no clue what that is.  Could anybody please shed some light on that?  And feel free to critique it if you'd like.