Strongly eroded unit Long/lat: from E, 24.12N to E, 23.87N Rational: This erosion feature bond to one particular stratigraphic level in the layered unit is likely due to softer rocks in this level than in the rest of the unit. These layers have likely recorded different conditions than the rest of the clay unit. Morphology & mineralogy: On the flank of Mawrth Vallis, some of the light-red Fe/Mg-smectite bearing layers show a particular erosion: many holes filled by dark sand. MSL tasks: At large scale, study the layering and erosion pattern and compare it to the rest of the clay unit. At small scale, study the grain structure, the mineralogy and chemistry of the eroded rocks. HRSC mosaic with HRSC nadir & color images

2 km HiRISE mosaic with HRSC & HiRISE color images

2 km HiRISE mosaic with HRSC & HiRISE color images Next slide Observation: We observe a similar kind of erosion over all the surfaces oulined by the white line.

Next slide 1 km This surfaces are characterised by holes of size ~10 m, of irregular shape, most of the time coalescing to each other.

100 m These holls are easily noticeable as they are filled by dark sand, acting as traps for the wind- blown sand.