mesas and buttes and such in parts of Meridiani, strong indications of extensive erosion over time. That doesn't preclude recent deposits of sulfates, et cetera, though.

Here's but one of many examples:
http://www.msss.com/moc_gallery/m07_m12/nonmaps/M10/M1001173.gif

The apparent absence of breccia at the Spirit site is interesting. While the surface may well be covered and covered again with the ejecta and debris of endless numbers of impacts, some of this debris should have consolidated, and we should see signs of it. We do not. In fact, there has been no evidence of breccias anywhere we have visited on Mars.

Why not?

The continuous action of fluids and ices may be responsible. Freeze-thaw effects seem to work everywhere.

In addition to the direct effects of impact on the surface, there are interesting signs in many locations that the surface has been heavily shaken. This is not like earthquake shaking that many of us are familiar with. It is more like the whole planet has been violently shaken -- which, if so, may be one of the reasons there is little or no cemented breccia at the surface.

I watched a sand table (it was pink garnet sand BTW) being vibrated one day, and the most astonishing things occurred. Depending on the intensity and velocity of the vibration, the sand would spontaneously form and reform itself into miniture geological formations, hills, mountains, forming inlets and peninsulas, islands, breaking up and reforming time and again. It was fascinating to watch and I was immediately struck by how some of these spontaneously generated formations resembled some of the more enigmatic Martian formations.

I wondered if some of what we see on Mars resulted from the violent shaking of the surface caused by impact or internal forces. I'm not sure that anything like this has ever happened on Earth.

Cheers, BRFelix