So I got SouthAtl map. WHat are those piles of pebbles to the left of Mt_Pleasant runway 28?

[DmitriKozlowsky]

So I got SouthAtl map.

Looks great from altitude. Looking to have fun with it.

What are those piles of pebbles to the left of Mt.Pleasant runway 28? Is it a buried tactical approach system? Or just pile of rocks.