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My observation is that the Bolivian circular earthworks appear to effectively prevent erosion in the lower rectangular plots. Quake damaged circles do show erosion at the faults.
I'd put forward the hypothesis that concentric earthworks attenuate the runoff speed and volume of pre-columbian terraced farmlands. They were designed and created for this express purpose. I propose a test be made of the hypothesis in some suitable and convenient location.
Too, I would speculate that irregularly shaped rectangular geoglyphs below the circular mounds were made by design in order to attenuate erosion. I suspect that agricultural plots were not individually owned, so having equal shares wouldn't be an issue.
Something is not right. This message is just to keep things from messing up down the road