[Graewoulf]

Looks like the structure above a salt dome. Any maps of this structure showing dips?

[petuniasevan]

I can't find any topo map of the structure.

Here's what a NASA page had to say:

"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."

http://eob.gsfc.nasa.gov/NaturalHazards/natural_hazards_v2.php3?img_id=2124