This view of the undisturbed surface of a Martian sand dune called "High Dune" visited by NASA's Curiosity rover shows coarse grains remaining on the surface after wind removal of smaller particles.
The image covers an area 1.4 inches by 1.1 inches (3.6 by 2.7 centimeters). It was taken by the Mars Hand Lens Imager (MAHLI) camera on the rover's arm on Dec. 5, 2015, during the 1,184th Martian day, or sol, of Curiosity's work on Mars.
The imaged location is near the base of the dune. High Dune, in the Bagnold Dunes field skirting the northwestern flank of Mount Sharp, is the first sand dune studied in place anywhere except Earth. What distinguishes actual dunes from windblown ripples of sand or dust, like those found at several sites visited previously by Mars rovers, is that dunes form a downwind face steep enough for sand to slide down.
MAHLI was built by Malin Space Science Systems, San Diego. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Science Laboratory Project for the NASA Science Mission Directorate, Washington. JPL designed and built the project's Curiosity rover.
More information about Curiosity is online at http://www.nasa.gov/msl and http://mars.jpl.nasa.gov/msl/.