you can't raid those valleys yet. they give a bonus to production in your main village if you pwn them. you need to destroy all those animals with your hero, have your hero's mansion at level 10, and then you can annex the valley. those animals are no fuckin joke though, don't even try to attack them without a few hundred units, and not some piddly ass phalanx or macemen either.
if the valley is say half clay looking and half wheat looking, then you get a 25% boost to clay and wheat production. if it's all wheat looking, you get 50% to wheat i believe. something like that anyway.