JMS,

Thanks as always. The paper I referred to was linked by Nick, not written. Some researchers at the Lunar & Planetary Inst arguing that very thin hematite coatings match the IR spectra seen (from orbit, at least) better than big old lumps of the stuff. Implication that there doesn't have to be much of it around for it to show up in TES.

http://www.lpi.usra.edu/science/kirkland/Papers/kirkland_lpsc03_abs1944.pdf

I think we're on the same wavelength on the issue of where water deposited material is found -- if that conclusion can be generalized (which it can't, but it's more fun if we make the connection for now). If there was significant planetary-scale circulation going on, whether on the surface or underground, over time those salt piles should have been transported north. If you have systems that are only damp and aren't connected more than regionally, then dissoved minerals stay put (regionally). After all, where do you find evaporates in the US? The Great Basin especially, which is both dry and lacking a well-connected drainage system.

The olivine point reminded me of those huge expanses of olivine-bearing cliffs in Valles Marineris. There may have been groundwater in Meridiani, but apparently not 2000km or so to the west.

Heh, unless we look in the big crater and find that underneath our evaporites is a big slab of unweathered basalt, olivine and all. That'd be a fun one to explain (assuming it was clearly not a recent sill, that'd be too easy).

Thanks for the Pikes Peak cam! I spent a summer in Colorado (Ft Collins) but never made it down there.

I was going to send you a link to a mountain in my old stomping grounds, but apprently the U.S. Forest Service considers replacing a webcam to be a year-long project.

http://www.fs.fed.us/gpnf/mshnvm/volcanocam/

At some point it'll show Mt. St. Helens. You get spoiled growing up in the Northwest; it's hard to get excited about mountains that just sit there.