[X] My Assistant

[GregM]

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[dvandorn]

Gusev was selected as a landing site because orbital photography *very* strongly suggests it once held a lake.

What we've found are the Columbia Hills, which seem to pre-date the lake phase of Gusev -- the rocks generally aren't water-altered enough to have been on the bottom or shore of the lake, so the hills seem to have been uplifted above the "water line" prior to the formation of the lake.

The other thing we've found are the basaltic lava flows that have covered the entire floor of Gusev. There is plenty of unaltered olivine in those basaltic rocks, showing that the basalt "cap" has never been significantly wet.

Somewhere in Gusev, there *must* be exposed lacustrine materials -- the rocks formed and altered on the lakebed and at its shores.

If there is any way to make a best guess at where we might be able to get to such lacustrine materials, and if they are even remotely within reach, I'd spend Spirit's last days getting there and looking at them.

However, I've got to think that we can't identify such rocks easily from a distance, and the landforms visible in orbital images thus far haven't been helpful in this regard, either. So, either the lacustrine materials are effectively buried and can't be reached by surface exploration, or if they can be, we don't know where to look for them.

(As an aside, I think we probably *have* seen one or two examples of lacustrine materials up on Husband Hill and West Spur, especially hematitic rocks like Pot of Gold, that were lobbed there by impact events. But since they've been loose rocks and not part of bedrock outcrops, you can't get any details on their context within Gusev and its history.)

-the other Doug