"Shaler Unit" - Sol 120 (Slightly Darkened Absolute Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga/Lunar Explorer Italia/Italian Planetary Foundation)

Caption NASA:"This image from the Mast Camera (MastCam) onboard NASA's MER Curiosity shows a bizarre-looking Stratigraphic Unit (known as "Cross-Bedding") located in an Outcrop called "Shaler". This Stratigraphic Unit has been informally dubbed "Shaler Unit". This kind of "Cross-Bedding" in the Shaler Unit is indicative of Sediment transport in Stream Flows. Currents mold the Sediments into Small Underwater Dunes that migrated downstream. When exposed in cross-section, evidence of this Migration is preserved in the form of Strata that are steeply inclined as to the Bed (---> River or Lake's Floor) they lay on (thus the term "Cross-Bedding." The grain sizes here are coarse enough to exclude an Aeolian transport.
This Cross-Bedding occurs stratigraphically above the Gillespie Unit located in the "Yellowknife Bay" area of Gale Crater, and is therefore geologically younger. The MastCam obtained the image on the 120th Martian day, or sol, of Curiosity's Operations (such as December, 7th, 2012).