OK Guys. Here's the deal. Those are man-made goose nesting sites. Back when we constructed the OTH-B sites, the Dept of the interior required the sites be built as we were disturbing their historic and natural environment. Cost an arm and a leg, don't think the geese tought much of it. During the rainey periods they keep the nesting areas above water and isolated from predators. Sorry, no indians, aliens or prehistoric time portal transfer switches. The rocks had to be be just so,, not too big, not too small. Thanks for the tax money.