The water run off of the Southern Mountain Range feeds the plants of a large
jungle, whose plants greedily drink up nearly all the water. What little is
left gets used up by the tall grasses and shrubs of the south plains. With
virtually no water left after that, the southern most region is nothing but
desert and sand.
This formerly inaccessible region has recently been scouted by Jed of
Miden'nir, who has a wonderful story to tell about it. See Jed and hear his
story of the Southern Plains, and maybe you'll get to explore them yourself.