There's no proof that the Pilgrims even landed on Plymouth Rock, but the Rock does have a fascinating history. Plymouth Rock is an American icon, a symbol of intrepid discovery, liberty, and freedom of conscience. From anywhere in Plymouth, Massachusetts, road signs and residents guide you to Plymouth Rock on the waterfront. The stone itself is granite, probably from a formation known as the Dedham granite, formed 608 million years ago (give or take 17 million years)—that is, a long time before 1620!