On the same picture as where I found the "whale" (see post below) near Mawrth Vallis I found these strange features. There are lots of them around this place and again I do not understand what they are. Maybe some mountain-hills overgrown by dune? Look especially at the work of the shadows. They seem to be some kind of arcs. Click on the picture for full size.
Here are some more of these features found a bit to the west and to the south of the picture above.
And here even more: