Horton,The bottom image of Reply 222 kin...

Horton,
The bottom image of Reply 222 kind of reminds me of what you might get if you mix up an handfull of mud with sand gravel and talcum powder.

From Reply 218 "Here":
Amazing stuff! Image # EFF89160121 shows a previously deposited gravel bar that is partially eroded. The eroded gully in the gravel bar has larger gravel pieces and no smaller gravel pieces indicating that there was a higher flow (higher transport energy) involved that removed smaller pieces of gravel. This shows that there was originally a fine to medium gravel bar deposited in a stream. Later there was a higher water flow going throught the channel. This higher flow removed smaller pieces of gravel leaving only pieces of coarser (larger diameter) gravel. I'm still not sure what the exact scale is but judging by the relative size it's obvious there were at least 2 separate events. Judging by the subrounded to subangular shapes of some of this gravel you can tell that some of it is very old and has been reworked (rerolled in stream beds) many times. Wind erosion and corrosion also tend to sometimes round sharp edges but some of what I see must be abrasion by other rocks rolling in a liquid environment.

There are other images in Horton's "here" link that show gullies with no gravel but gravel surrounding the gullies. In these gullies the gravel was swept away in the channel and there was no heavier gravel present. I could be wrong but these features do seem to imply flowing water.