Note also that evaporates (sulfate or carbonate) seen on *top* of rocks in Gusev also supports the idea of atmospheric deposition of liquid water in Gusev:

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Newsgroups: sci.astro,alt.sci.planetary,sci.geo.geology,sci.geo.mineralogy
From: rgregorycl...@yahoo.com (Robert Clark) Date: 2 Jul 2004 04:57:20 -0700
Local: Fri, Jul 2 2004 4:57 am
Subject: Evidence for atmospheric liquid water in Gusev?

In the badastronomy.com forum Daniel Crotty presents an image (below)
showing white colored material on *top* of rocks. This would argue
against the interpretation suggested by Steve Squyres that the
sulfates seen in Gusev might stem from water percolating up from the
subsurface. Instead it would suggest sulfates formed from liquid water
precipitation(rain) or liquid water droplets in a humid atmosphere.
I wondered whether white material on the rocks could be due to the
dust kicked up by a RATTing but Crotty gives other images with no
ratting nearby that also shows white rocks:

Dusty, bright material around Spirit, Sol 165
http://badastronomy.com/phpBB/viewtopic.php?t=14573&sid=7f6b82d247999...

Bob Clark

Uncalibrated color image by Daniel Crotty.