Image taken on Sept. 28, 2012 and spotted by Scott Warring of http://www.ufosightingsdaily.com/. As per Mr Warring - "Note its lighter color upper and lower eyelids, its nose and cheek areas, its ear, its front leg and stomach."
Debunkers have pointed to the phenomenon known as pareidolia and the similarity in coloring to its surroundings, implying it is probably just a rock. Pareidolia is psychological phenomenon inherent in Humans, possibly derived from primitive survival instincts to pick out familiar forms and faces from everyday objects and structures. Such as Prey and predators.
The shading or coloring of the alleged rodent actually does not match its surroundings perfectly - it has shading and light and dark spots exactly where you would expect to find them on such a creature, and it appears to be foraging, exactly as such animals do on Earth
Also note that there appears to be a light trail going from the right of the picture leading up to where the anomaly is located when the image was taken. The trail consists of loose soil that has recently been disturbed - presumably by Marvin the martian chipmunk we see in this image.