Stone ledge may have had a slight depression in the stone layer. Clay liner was definately not soft in that spot or pond would have leakage symptoms. Pond is very tight and banks are well packed. Hole margins and cavity were very firm when I probed it with my boat paddle. Do you suppose CC use their spines for lossening the soil? I wish I could get a good photo of this cave. It is far enough underwater that a photo is difficult.

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