Pit/Crater close up

This is a close of of the pit on the far left of the pan taken on Sol 379. It would be interesting to see closer to the pit to see if we could understand what causes these. Presumably there is a hard surface in the center of the pit an the dust is blown away while the round hematite marbles ("blueberries") are able to roll to the edge. This doesn't explain why the patch is bare unless there are wind gusts of sufficient velocity and frequency to roll the marbles back onto the plain. If we could calculate the average marble mass we could speculate on the size and frequency of these gusts. Of course there may be a different mechanism to clean these spots.