I imagined Plymouth Rock a formidable hunk of granite sheltering the rocky shore, noble and impressive, a landmark visible from sea, like you'd see on the Oregon coast. HA! HA! It's a smallish chunk of broken boulder placed on the beach in Plymouth Harbor, protected from tourists by a portico built for the 300th anniversary of the landing. The structure covering it is more impressive than the rock.
To see more pictures of historic Plymouth, here's a link: Plymouth