This image shows layered sedimentary deposits in Candor Mensa, a broad plateau of thickly stacked sedimentary rocks in Candor Chasma, part of the giant troughs of Valles Marineris.
Valles Marineris is a system of tectonic depressions formed by down-dropping faults; the floors are among the lowest points on the surface of Mars, and may have once held lakes. Some sites show evidence for streams or rivers. The troughs may have also been sites of volcanic activity.
Currently, the deep floors contain massive deposits of bright sedimentary rocks. Some of the deposits are several kilometers thick, and have diverse composition and appearance. They were probably formed by many different processes in different environments.