"Great Island is not an island at all but rather a long coastscape of shore, sand dunes, and upland. It is a classic barrier beach, much like Long Point in Provincetown, Nauset Beach in Orleans, and Sandy Hook in Barnstable. Each parallels the mainland and protects interior bays, harbors, and marshes.
In the past, Great Island was a “stand-alone” environment. It was a true island into the early 1800s and is now the chief upland of this land mass, rising 0.5 mile south of the parking lot. (Another natural feature of this hike, Great Beach Hill, located farther down the barrier, was also surrounded by water at one time.)"