Isolated Pile by the water

A bit of water between the hills just south of Holden Rd Shirley. The area is full of rock piles but how many times have I passed this place (2 or 3 times before) and not seen anything? 

I only noticed it this time because I sat down a few feet away to catch my breath. After a moment or two I spotted it:

 

These piles can be very easy to miss.