New Mars Forums

Well, there are two extremes when it comes to Ultreya or the so-called Inner Basin.  The "professional scientists" believe it is wind blown dust that is in the shadow of the northern cliff face.  On the other extreme, "amateur observers" believe it's the opening to a very deep cave system formed through some surface hydrogeologic process. 

I'm basically in the middle.  I don't think there's enough evidence to call it a cave in the true sense and I don't see any evidence for water action on the surface of the degraded crater.  At the same time, the stereo images I posted seem to show not only a vertical face but also a curvature and depth to the layered units exposed on east walls enclosing the black feature.  So I'm leaning towards a collapse feature of some sort, perhaps related to the interaction of ground water with the more friable units of the layered strata.  Or it might even represent a second, later impact event that broke through the layered units.

The bottom line, in my opinion, is that there is insufficient resolution in the images released so far to make an assessment that is 100 percent accurate.