Sources of Basaltic Sand (extra-detail mgnf n. 1; MULTISPECTRUM - credits: Lunexit)

This image was targeted at a point in Mitchell Crater in the Southern Highlands of Mars where sands abruptly appear and spread North.
The sands seem to derive from the edge of an eroding mesa (shown here with an arrow; 8,66 Km, or about 5,4 miles across).
A close-up view of the terrain nearby (see the extra-detail mgnf n. 2) suggests that boulders and sand have been excavated by erosion from beneath brighter, polygonally fractured ground (1,45 Km, or about 0,9 mi across).