This is an island that has been logged, and logged, and logged. The biggest parkland area was acquired in a deal with a forestry company, and it has been logged and is growing back, slowly. One of the things that turns up in that land, obviously, is stumps.
And an amazing number of stumps with Really Big Rocks sitting on top of them. (We’re talking about rocks of a size that unaided humans cannot lift.) I gather that workers with backhoes and a sense of humour have had something to do with the presence of Really Big Rocks on top of stumps. Whatever the explanation, the junction of rock and wood produces some interesting effects.