CharlesE wrote:... I suspect the boulders were left behind after smaller particles moved away. The boulders don't appear to my eye to be laid down, as debris from the asteroid collision. I would expect collison debris to be spread at random and to be oriented in different directions. In general, the boulders are oriented in similar directions and generally form a somewhat planar surface.
Sorry, I didn't mean to leave you with the impression they were blown around by the crater making impact. Rather these rock layers are more or less where they originally formed. They were cracked during the crater-making impact and subsequent rebound of the surface, then the forces of erosion took over. Some of this erosion would have occurred around the edges of each rock chunk because the wind (or water) would have sped up there. Undercutting of the chunks can occur when the erosion process encounters a softer material under a harder layer, and can eventualy lead to some of the chunks being undercut so much that they tip over in relation to the general flattish layer, but most will remain roughly aligned with each other, as we can see in this picture. Also, softer layers on top would eventually be removed entirely by the erosion, becoming part of the sand and dust. I don't know if we can tell how much material has been removed from above these rocks and blown away, but it is likely a significant amount. After all, Gale Crater is about 3.5 million years old. There's been plenty of time for a lot
of erosion, however slowly it may occur.