It is a section of what looks like sedimentary rock showing significant water activity over an extended period of time.
At least three different wet periods of time can be inferred here. The lowest section is mudstone. Mudstone is deposited in still or slow moving water, like a lake or river delta.
But that mud dried up, solidified into stone and then cracked. At a later time the soil again became moist, but only slightly. A whitish mineral was drawn into the cracks leaving the white veins.
At an even later date sand was deposited on top of the mudstone and solidified into stone itself. Sand deposition indicates a moderate water flow, like a beach or river.
All in all that picture tells an interesting story about water on Mars.