Posey Island State Park is a small, one-acre marine camping park with 1,000 feet of shoreline. It is located a quarter mile north of Pearl Island, near Roche Harbor, San Juan Island. Posey Island is part of the Cascadia Marine Trail. All onshore campsites are for the exclusive use of boaters arriving by human- or wind-powered watercraft. The island was originally thought to be part of Pearl Island and was called Spit Point. When the U.S. Coast and Geodetic Survey were mapping the area, they asked local folks what they called it. Since the locals went there to pick flowers, they called it Posey Island, and that name was applied on the maps.