Whatever it is certainly looks totally incongruous with the rest of the landscape, so much so that I at first thought it was a 'photoshop fake'.
However, it's obviously a nasa image hosted on a nasa server, so I assume it isn't!!
If you look to the left of the anomaly, along the brow of the dark ridge there's also a tiny sliver of something the same colour.
Not sure what it could be, but it does look artificial, kind of like a big sheet of crumpled foil.





