March 21, 2007, HiRISE release

Richardson sand dunes - rocks in between the dunes I can understand, but on the dune crests? Or are these dunes so low-profile that the rocks resting on the underlying surface poke through? It doesn't look like that at first glance (but I've only viewed the 'browse' version). Displaced chunks of frozen dune?

I think these are just black spots on the sand. Some of them look similar to boulders, but only because there are real boulders nearby. It's interesting that most of the spots are on the crests and very few are on the slopes.

I think (without going back to check the press release... I'm lazy and too short on time)... that the dunes are still mostly covered in winter frost (CO2 ?) and the black spots are defrosted areas.