Mystery on the Rock

 

Bodega Rock, off the southern end of Bodega Head, on 20 June 2013.  On the far horizon, from left to right, are the sand dunes of Dillon Beach, the entrance to Tomales Bay, and the high bluffs of Tomales Point.

A little bit closer:

 

And even closer, so you can now see the nesting colony of Brandt's Cormorants on the upper right (west) side of the island:

 

I'll zoom in even a bit more for a view of the cormorants sitting on their mounded nests.  And also because there's a mystery object that I've been wondering about (see arrow in next image).  

 

There's a relatively obvious human-made object on the island — it's gray, somewhat rectangular, appears to made of concrete or something similar, and as you can see above, it's about as tall as a cormorant.  It seems like this is as good a place as any to ask if anyone knows the story behind this object.  Do you know what it used to be?  Who installed it and when?  Feel free to write in if you know anything about it, or can suggest any leads for me to follow. 

P.S.  And yes, those are California Sea Lions (brown) and Harbor Seals (gray) lounging on the rocks near the water line.

P.P.S.  Happy Solstice!