Regions excluded from the mapped extents of sinuous rilles (Fig. 1) for crater counts in this study (yellow striped-filled, red striped-filled, and black outlined regions) and their detailed views. (a− d) The northernmost ~70 km segment of Rima Sharp with U-shaped cross-section profiles and very steep inner walls (yellow striped-filled region) and the secondary crater clusters (black outlined regions) crossing Rima Harpalus. (e− h) The secondary crater clusters (black outlined regions) crossing Rimae Sharp and Mairan and the connected segment of the two rilles (red striped-filled region). The basemaps are all TC morning mosaic.