You're very perceptive! That's not moss - but it's not far from daylight.
Yes, there's a fair bit of geological interest in the picture.
Yes, the displaced bedding plane is clear, so definitely a fault rather than a joint. But this is a "strike slip fault" (i.e. mainly sideways movement) so the actual amount of displacement is a lot more that it appears from this photograph.
The paler rock high up is a porcellanous bed similar to (but not necessarily the same bed stratigraphically as) the better known PB in the GG system.
None of which gives you much in the way of clues. So I'll give you one; the noise made by the pile of rounded pebbles, which rattles away when disturbed, is the original reason for the name of this place.