The top image shows gives a clear view of the full body of the millipede. There are 20 countable body segments. This is apparently diagnostic for members of the Polydesmida family, which all have between 18 and 22 segments. Because the colors had all been bleached away by time, it would be hard to identify down to species. The family gets its common name, flat-backed millipedes, from the lateral blade-like ridges, called paranota, poking out from the sides (apparent in photo at bottom of posting).
Differences between millipedes and centipedes: The image below shows a single body segmented with two pairs of legs. Millipedes have 2 pairs of legs per segments (centipedes have 1), short legs that don't extend much beyond their body (centipedes have long legs), they don't bite (they're scavengers, centipedes, which are predators, do bite), and millipedes are slow (centipedes, again are hunters and are very quick).
Where: On the moss-covered rocks at Rock Point