re: Ebenezer and Clovis suggest volcanism
I listened to last weeks teleconference today and Steve Squyres gives one reason why the rocks in the Columbia Hills were watered altered.
The audio of the teleconference is available here:
JPL.NASA.GOV: Mars Exploration Rover Briefings
http://www.jpl.nasa.gov/missions/mer/briefing.cfm
About an hour in, he says in the Gusev plains we see numerous rocks with olivine, which he says is a common mineral in fresh basaltic rock. However, he says since reaching the hills, we haven't seen any.
This alteration though may have come through water-volcanic interations such as with maar-type eruptions.
Bob