Deuteronomy 11

29 These two mountains, west of the Jordan, are very similar to one another in size and shape. They rise about 800 feet above the small valley that separates them. Gerizim is on the southern side of the valley while Ebal is on the northern side. It has been observed that from the valley, Gerizim is fruitful while Ebal is not. This is thought to be because Ebal's south side, scorched by the sun, faces the valley while Gerizim's shaded side faces the valley (TSK).