re: Further...
Sabkha:
The low-lying sabhka is a landscape of sand cemented into a fragile crust by the alkaline minerals of a high water table. Due to the high water table, moisture is plentiful (despite only seven inches of rainfall per year).
http://www.nps.gov/grsa/resources/lifezones.htm
Sabkha is an arabic name for a salt-flat ordinarily found nearby sand dunes. These relatively flat and very saline areas of sand or silt form just above the water-table where the sand is cemented together by evaporite salts from seasonal ponds.
http://www.handsontheland.org/glossary/glossary_details.cfm?ID=359
http://gsa.confex.com/gsa/2003AM/finalprogram/abstract_58753.htm
Where's the salt, anyway? Sulfurous deposits suggest the possibility of fluids emerging at the surface from below. And would such deposits "dissolve" in the air? What of the possibility of chemical reactions between the dark overburden and the light-toned sulfurous deposits?
Some of the features here are impact craters, but some are not. The scene is Meridiani near the Opportunity landing site.
http://marsoweb.nas.nasa.gov/landingsites/mer2003/mocs/Images/R01-00630/R01-00630.jpg