If you use your imagination just a bit, there is a rock that is a spitting image of a classic Alien "Grey"! You know - big cranium; dark slanted eyes; face narrows down to a small mouth. It's great! Now that I think about it, it kind of looks like the "Iron Man" mask as well. Ha-ha!
The following images are cropped to show the area of interest (You can click on them for a better view). Also, like I mentioned above, head over to NASA's JPL site to check out the full, hi-res image of the entire landing site - pretty cool stuff.