Kenya and Tanzania -- Oct 2012 -- Part III of III

The triangular dark area is a a forested region, with surprisingly sharp boundaries. Looks to me lke the trees are growing on an eroded lava flow coming out of the group of (similarly dark) cinder cones in the distance. I suspect the trees are there because the "lava flow" (if it is indeed what I suspect it is) has eroded into richer soil than the surroundings, or else into soil that is better at retaining moisture (or both).