When I first saw this phenomenon, fairly early in the mission, I got to thinking immediately of dried mud. Whether or not the soil covered the slab (which it likely did at one time), the little scarp edges need something more than long-gone muddy conditions for their preservation today... what could it be?

When word came about the location being "drenched in water" at one time (or many times) it seemed simple enough to imagine that we're seeing the result of a contemporary reaction between the soil and the outcrop, in which water acts to help cement the soil grains in contact with the outcrop. The scarp itself may be quite dry now -- but then again...

Several things to consider: apparently frost forms on the lenses of the cameras at night. If so, then surely there is frost all over the surface, likely every night. What happens as it sublimes from the surface of the outcrop each morning? Couldn't the water vapor and whatever contaminants it may be carrying (oh, salts maybe?) be helping to form the scarps by cementation? In other words, might this be a current -- and ongoing -- phenomenon rather than an ancient and eroding one? (of course, why couldn't it be both at once?)

Another thought: if the outcrop was once wet, could it still be wet? Apparently there is no test for wetness on the rover, more's the pity, but is it possible that subsurface water is still percolating through the formation, drawn to the surface and subliming therefrom? Or would any water at present be frozen solid at all times? (Surface temperatures can get pretty clement in the daytime, though, and such a salty/sulfurous environment may prevent water from freezing under average temperature conditions anyway... )

I'm also wondering about temperature differences: the surface of the outcrop is very reflective whereas the soil surface is very dark. Wouldn't the soil surface be relatively quite a bit warmer than the outcrop surface throughout the day? How would the temperature differential affect the formation of soil scarps -- if at all?

Cheers, BRFelix

(It is interesting too that Steve Squyres was apparently asked about the muddy appearance of the soil near the lander and suggested that it actually might have been muddy thanks to the release of water from the vehicle as it landed. On the other hand...)