Does that look like WET SAND or what?
Opportunity roll off pics sure look like the trails we made at the beach last summer with the kids cooler as they dragged it a load in it, left the same type of cupped depressions in the sand, along with being wiped out when the tide came in and covered over the tracks....Besides, it can't be frozen (freeze point on MARS is?????? if liquid water is present?) so we guess it's either all wet or subsurface hydrocarbons are there.....maybe 3 in one OIL?