The rocks that the standing stones were constructed from were quarried from natural cliffs in the local landscape. The rock is predominantly that of the Old Red Sandstone which was laid down during the Middle Devonian approximately 390 million years ago. The sandstone was deposited in a large lake, Lake Orcadie within the larger Orcadian Basin that today covers most of Caithness and stretches far into the North Sea. The nature of the sandstone with its fine laminations gives the rock a natural flagstone character that allows it to be broken up into the characteristic slabs. Geological evidence of the shallow lake shore environment during deposition can be seen on many of the slabs in the form of ripples with crests 10-20cm apart.