If it is possible for water -- or something else -- to remain fluid close to the surface (and you've repeatedly shown evidence that water can remain fluid at the surface during parts of the day) then the "percolation" scenario has to be taken seriously. Because of pressure differences, it seems to me that any subsurface fluid would be drawn toward the surface if there were any access to the surface from below. We're told by some that the permafrost layer is utterly impermeable and consequently, any subsurface fluid water would be forever imprisoned beneath this impenetrable layer. Yet there are signs all over the planet, recognized for decades, of apparent percolation of water and other fluids from below.

Percolation would be unlikely to leave coatings on competent rock -- instead, it might leave deposits, such as the festive "pot o' gold" type formations.

The atmosphere is always pretty much saturated with water vapor so I'm led to believe. This is still very dry by terrestrial standards, but it's as "wet" as can be by Martian standards. We see plenty of evidence of light frosts and heavier frost/snow deposits resulting from deposition of atmospheric water. So why shouldn't there be deposits in Gusev?

The question for me is what is coating the otherwise dark rocks here and elsewhere (if they really are dark beneath a light coiored coating). Are they bleaching in the sun? Is that magical UV radiation causing them to lighten? Or is there a veneer of sulfate or something else?

I'm also intrigued by the erosional shapes we see -- the beautiful curves and the extraordinary angular shapes. Some of the rocks look sculpted -- no doubt by aeons of erosion, but still.... ;-)

Could the area have been submerged in water (or an aqueous acid solution?) Sure. Why not?

Still more intriguing is the nature of the "rotten" formations with all the complex protuberances and such, some of which seem to be fitted neatly inside "boxes." This juxtaposition looks inexplicable.

Some rocks have been crushed by the wheels of the rover. This indicates that these rocks are not competent rock at all but instead are more akin to deposits -- sulfates, salts, whatever. I saw a picture of what looked like one of those baroque model "pot o' gold" rocks that had apparently been partially crushed -- perhaps by pressing the rover arm against it (it didn't look like ratting). From the appearance of the black and white image, the subsurface was white and soft. I don't know whether Squyres discussed this or not.

And as for the sparklies... I suspect it is a matter of the salts or whatever they are....

Cheers, BRFelix