On the west or left side of the cave are giant grooves made by the passage of one rock body against another. This sea cave is also a fault zone. One fault can be observed on the upper right side of the entrance. The Altamira shale which is 10 to 17 million years old makes up the rock here. When angular and broken, it is called breccia. When rock is ground up by the tremendous forces, it is called fault gouge. It may be seen as a thin ribbon in the fault zone. Some of the cobbles along the beach are blue and green from the metamorphic rock, Catalina schist which is over 100 million years old.