Joined: 21 Apr 2010
Location: Somewhere in the City ...turned to stone
In the last example above, the inner ring is partially obscured by the plant life and has largely worn down; but you can see a clear difference in the soil color and in the apparent fertility level, a good indicator that there is an important difference between the inner circle and the stretch of land between it and the obvious outer ring.
So more food for thought!
BTW, the difference in the plant life in the middle of the crater may be because the crater is a closed basin. Any rainwater falling in has nowhere to go and forms a lake in the crater. The water eventually evaporates and leaves salt and other minerals behind.