Corduroy Dunes

This image from NASA's Mars Reconnaissance Orbiter (MRO) shows the permanent polar cap of Mars, encircled by sand dunes and looking like pulled threads, these dunes march across a fabric of patterned ground.

At this time of the Martian year the dunes are free of the seasonal dry ice that forms a temporary cover every winter.

https://photojournal.jpl.nasa.gov/catalog/PIA22464