The God Tree's roots are astral lines of power that stretch all the way from Muraius, through Mt. Helicon, and deep into the earth. The High People believe that Yevna's presence can be felt anywhere on the earth through these ley lines, and that the Great Crystal allows them to channel its power.
After The Fall, the ley lines have weakened, and only those in tune with the voice of the goddess can hope to find them and tap into the magic that radiates from their veins.