Sol 4410, June 20, 2016; Rover Field Report by Larry Crumpler, MER Science Team & New Mexico Museum of Natural History & Science: Opportunity is finishing up its activities here in Marathon Valley on the western rim of the 22 km-diameter Endeavour impact crater. Over the past few weeks it has been “walking” along a ridge inspecting the outcrops. From orbit this location was spied as containing significant clay minerals, so the rocks here have been studied carefully.
(…) Marathon Valley is an unusually deep “cut” in the rim of Endeavour. This may be part of the reason why we are seeing something a little different here. But maybe not. Science can be peculiar that way. (Which is why scientist tend to be skeptical of everything and test everything. When a bunch of scientist start saying the same thing, then you have some pretty significant results to talk about.) [More at link]