Mars: Chemical ratios indicate gradation by water

Chemical analysis: That means, "The way to explain the various chemical-ratios in various rocks is through their interaction water."

See, "Chemical Changes in 'Endurance' Rocks" discussion on the graph here.

Links: More on the analysis; JPL press release. Google

Image of canyon-route: Image showing lines -- how they plan to move the rover. You can see the heat shield to the left, and the target-rock to the right. There's an arrow also showing the canyon the rover might be able to drive if needed.

See the "Opportunity Escape Plan" here for larger images and a discussion.