[Axenolith]

It appears that the soil in the sunlit portion is more smooth, or "deflated". That would bolster the frost heave theory, as the heaving material would probably sublimate (whether CO2 or H2O) and dissappear upon lighting and IR absorption and they lander shaded area would hold together for longer. Now, under that theory, it would simplify things if there is a subterreanian (and possibly renewable) source for the fluids to wick upward under cappilary action during warm periods.

That, BTW, would also create a nutrient and salt transport mechanism in the subsurface for any critters that might make the soil column home. The only downside is, unless they cycle dormant near surface with seasons or days, they would be below the frost depth, which is probably below the landers drilling\scooping capability.

[RightWhale]

the fluids to wick upward under cappilary action

It's -42 here today. There is no liquid phase water on exposed surfaces except in the river near the power plant outlet (non-toxic, for those whose knee is twitching,) and there is no liquid wicking up. However, the gas phase of water is migrating. As long as the air is quiet hoar frost continues to build on all exposed surfaces. It can get several inches thick near the river after a couple weeks. The gas phase of water transitions to the solid, crystalline phase and vice versa very easily even at 40 below zero.