What if... not everypony wanted to come to Equestria to escape from the Windigos?
What if... by some crazy chance... half of the Earth pony tribe hated pegasi and unicorns SO MUCH that they DIDN'T trek over, and instead found refuge someplace else?
And... what if.... before the feud, the tribes occasionally married into one another?
Sooo... the prouder half of the Earth pony tribe manages to stay behind and survive inside of a mountain cavern. They call themselves the "pure ponies," believing that they are the original and best species.
There's a natural spring in this cavern that they're living in, and mysterious glowing "sun stones" tha