 The island has a permanent size of , plus an intertidal zone of a further , and is composed of two drumlins, reaching an elevation of above sea level, and connected by a marshy lowland.Tidal sand spits extend from the west end towards Weymouth Neck in Webb Memorial State Park and from the east end towards Slate Island.As a visitor attraction, Grape Island offers trails, rocky beaches, and camping in wooded campsites.