It's a truly anomalous piece of terrain: when you try climbing it, you can see the flat terrain under it.
It's really a strange level design decision... it doesn't look good. It's like something put in to test the engine, but was left there mysteriously.
I can't find any discussions about this weird "spike" on the net either.
But I know for sure, that if I would create an epic easter egg, I'd make some kind of puzzle around something you barely notice -- yet something where your subconscious feels that it's strange, yet your conscious mind thinks nothing of it.
The spike is a perfect example of that.