A landform on Mars that consists of parallel ridges and troughs with an average wavelength of 18–51 m. They resemble sand dunes, but have formed by wind erosion of softer bedrock from a more coherent rock. PBRs are aligned transverse to the prevailing wind and the scientists who identified them believe they were formed by high winds that eroded the windward sides of the ridges and were deflected into the air, causing erosion on the lee side as the wind sank.