From National Geographic Space Pictures This Week; April 15, 2013:
Rock Jumble U. Arizona/NASA
The High Resolution Imaging Science Experiment (HiRISE), orbiting the red planet on the Mars Reconnaissance Orbiter, snapped an image of large rocks on the floor of an impact crater in an image released April 10.
The fragmented rocks, greater than three feet (one meter) across, are mixed in with smaller, fine-grained particles. This type of mix is called megabreccia, and usually results from impact events like a meteor hitting a planet.