[I agree with you on this. I think this particular feature on Mars is an eroded layered dome. The only thing that makes me think it could be an impact crater is what looks like a ‘splashed’ ring of material around it. It could also be the sediments eroded from the dome. But what eroded it, if it is a dome?]

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Just as in the Sahara, I would say that wind and dust can do a lot of damage.

Take a good look... there are 'splashed' ring features on this one too:

Mauritania's Richat Structure, Sahara:

Another view of Richat from space. (Could pass for a MGS image, esp. due to the color)

Another view with explanation:

[Initially interpreted as a meteorite impact structure because of its high degree of circularity, it is now thought to be merely a symmetrical uplift (circular anticline) that has been laid bare by erosion. Paleozoic quartzites form the resistant beds outlining the structure. The reason for the high degree of circularity is not clear.]

Circular anticline and 'folds' explanation:

New image of Richat by Landsat and explanation/description:

The so-called Richat Structure is a geological formation in the Maur Adrar Desert in the African country of Mauritania. Although it resembles an impact crater, the Richat Structure formed when a volcanic dome hardened and gradually eroded, exposing the onion-like layers of rock.

This image was acquired by Landsat 7's Enhanced Thematic Mapper plus (ETM+) sensor on January 11, 2001. This is a false-color composite image made using shortwave infrared, infrared, and green wavelengths. The image has also been sharpened using the sensor's panchromatic band.

So, there's a good chance that the 'partially-exhumed crater in Terra Meridiani' is an eroded volcanic dome.

Marcia
-Thanks, REB... you beat us to it. Had to look it up for myself though. :p