Devarim 11:29 says:
וְהָיָה, כִּי יְבִיאֲךָ יְהוָה אֱלֹהֶיךָ, אֶל-הָאָרֶץ, אֲשֶׁר-אַתָּה בָא-שָׁמָּה לְרִשְׁתָּהּ--וְנָתַתָּה אֶת-הַבְּרָכָה עַל-הַר גְּרִזִים, וְאֶת-הַקְּלָלָה עַל-הַר עֵיבָל.
And it shall come to pass, when the LORD thy God shall bring thee into the land whither thou goest to possess it, that thou shalt set the blessing upon mount Gerizim, and the curse upon mount Ebal.
Why was Mt. Gerizim chosen for blessing and Mt. Ebal for curses? It seems like it could just have easily been the reverse. When telling us which mountains to use, the Torah doesn't give a reason why one mountain should be chosen for blessing, and the other one for curses. It would seem that there must be a reason why.