That certainly LOOKS like stream-sorted gravel. PODROCK! HELP!
But that kind of depositional feature doesn't last long on earth, it is usually eroded away or covered up.
If that is evidence of an ancient Martian stream, how ancient? Could an old stream bed simply lie on the
surface for any length of time at all without being modified beyond recognition? I realize erosional
processes are slow and subtle on Mars, but they surely aren't non-existent. That looks like it was
underwater just a few days ago.