This portion of a color mosaic taken by NASA's Mars Curiosity rover shows strata exposed along the margins of the valleys in the "Pahrump Hills" region on Mars. The scale of layering increases upward, providing what's called a "thickening upward" trend. This is consistent with a variety of ancient environments, in particular those that involved water.
This image was taken by the rover's Mast Camera (Mastcam). It has been white-balanced to show how the scene would appear under Earth's lighting conditions.
Image credit: NASA/JPL-Caltech/MSSS