OK, I'm filing this under Ramblings as there's imagery involved that could potentially be useful for some project or other, but this is tenuous at best. It should go into the Photo category, except there isn't one and I'm not about to start a new category just for this one entry.
Public domain photos
. This link leads to page two of the search results for 'rocks', which includes some lovely sliding rocks. There's loads of good pictures on the site.
For what it's worth here's a link to the researcher's site
that tracked these rocks using GPS
. Each rock is given it's own name (female) and it's own website, though they were last updated in 1996. Fascinating stuff.