Reference pack by Ref-G
http://www.fotoref.com/products/mossy-basalt-boulders-1?variant=2434358771736
A valley filled with eroded basalt boulders.
The fluted pattern on the rocks is more accustomed to limestone karst formations. These much more durable rocks have been eroded by slightly acidic tree roots millions of year ago.
You will find plenty reference of mossy rocks piled on each other in this photo pack. It also includes a stream of dark brown water running through.