noenrad, that is a good question! In this instance, as in several other similar instances, most of the surface rocks, and look of devastation, is "ejecta", which has resulted from meteor impact. Here, where the horse statue is, is what has been named "Concepcion' Crater", and it is an impact crater. That is why rocks and "stuff" is just strewn everywhere. Now, who can say whether it is actually the result of a meteor, or the result of an incoming.....................??
Another point, you mention "large rocks" ---- in some of these Rover photos, it is pretty hard to actually perceive the size of an object, rock or whatever. Sometimes what we see as "large", may actually much smaller than we might think. It really is hard to know the object sizes, in the Rover photos, without some point of reference.
norenrad, I hope this helps!