Sol 4119, August 26, 2015; Rover Field Report by Larry Crumpler, MER Science Team & New Mexico Museum of Natural History & Science: Opportunity is moving down into a large valley that cuts through the rim of Endeavor crater. The valley is somewhat like a chute directed into the crater floor, which is a long ways below. So it is somewhat scary, but also pretty interesting scenery….
Of course the whole point of the investigation is the fact that alteration like the type we are seeing requires a lot of water and we want to know when it was there and how it moved through the rocks. Then we can get a better idea of how water may have played a role in the environment on early Mars. The crater rim is very eroded, so there was water all right. [More at link]