Dogs obsession with rocks

Question
My dog has an obsession with rocks.  She will pick them up, carry them around, drag them around with her paws, and will chew down trees and shrubs that are in her way.  She's rather gentle with these rocks, which are often fist-sized and bigger, but can be a little possessive when it comes to them.  She doesn't chew the rocks at all, so I'm having trouble finding answers online as to why she does this.  Any thoughts?

Answer
Todd;
Some dogs have toys of different things that they get into.
Rocks are probably something she was exposed to quite a bit when she was young...and she started playing with them.
I would not have a definitive answer for you.
Best regards,
Melissa