The barrier island stretches from the mouth of the Merrimack south almost to Cape Ann — a long, narrow strip of dunes, salt marsh, scrub pine, and tide-scoured Atlantic beach. The northern end has a small settlement of summer cottages and year-round homes; the southern three-quarters is the Parker River National Wildlife Refuge, where the road is a one-lane gravel track and the only buildings are a couple of ranger stations and boardwalks out to the beach.
In summer the beach is full at high tide and almost empty when the water drops; in winter the same beach is one of the wildest stretches you can drive to in coastal Massachusetts. The crossing from Newburyport is via the Plum Island Turnpike and a small bridge over the Plum Island River.