Enigmatic Canyon Dunes

This image shows a cross-section of ancient canyon systems in east Coprates Chasma, and displays several orders and generations of wind-driven dunes and ripples, also called bedforms. Some areas display more modern bedforms, often termed mega-ripples, which have likely been active over long timescales and have migrated in the recent past. Other areas along the canyon wall have larger bedforms that show a very different appearance. Although they have a spacing that would make them similar to typical Martian sand dunes, many display superposed craters, indicating they have not migrated for a very long time, possibly hundreds of thousands of years. https://photojournal.jpl.nasa.gov/catalog/PIA23530