What do you think of the thought I believe I saw elsewhere in these comments that these were intended as a way to conserve water? Is there any sign that the center of each circle is lower than the edges? Is there any sign of planting occurring in the center? Also, would this just be a good way to prevent rapid runoff if this area is subject to rare but intense rains?
I once read of agricultural practices in a place (I think the Azores or Canaries) where somewhat funnel shaped pits were made, perhaps 8 to 10 feet in diameter so that a plant could be set at the bottom to grow with maximum water and minimum wind exposure.
I really have no idea, the entire phenomenon is simply too huge to be what we think of as agriculture.