re: Desert around Opportunity not as smooth as it looked
This appears to be duricrust formed post whatever caused the gully rather than rock aka outcrop? It looks very much like it is forming over the surface of a dune. A surface duricrust containing hydroxylated sulfates is certainly compatible with the Odyssey gamma/neutron data of this area but if its formed over the surface i.e. "recent" then its not compatible with a "wet' model but rather a dry, aerial deposition.