Water ripples are forming in very shallow water of a Piedmont stream as it flows over orange bedrock. The rock is a metamorphosed argillite (fine-grained sedimentary rock) whose present color is the result of weathering in an oxygen-rich environment. Algae has grown preferentially in planar, nearly vertical fractures in the rock called joints.
The stream is in Uwharrie National Forest, North Carolina.
Image © Andy R. Bobyarchick.