Ben, Wha?
I can see it now...going for a suspected clay rich site, then getting there only to have one of those, wait a minute moments, only to discover the suspect clay is actually a new hydrous sulfate, or whatever, that forms on Mars only. That would be a kick in the pants. Actually a real concern though. I think an alluvial fan should be a target but unfortunately, the landings sites are not very lander friendly. After landing. some distance would have to be navigated to reach the area of interest. Worth the effort I will predict.