The swamp was formed over the past 6,500 years by the accumulation of peat in a shallow basin on the edge of an ancient Atlantic coastal terrace, the geological relic of a Pleistocene estuary. The swamp is bordered by Trail Ridge , a strip of elevated land believed to have formed as coastal dunes or an offshore barrier island. The St. Marys River and the Suwanee River both originate in the swamp. The Suwanee River originates as stream channels in the heart of Okefenokee Swamp and drains at least 90% of the swamp's watershed southwest towards the Gulf of Mexico. The St. Marys River , which drains only 5–10% of the swamp's southeastern corner, flows south along the western side of Trail Ridge, through the ridge at St. Marys River Shoals, and north again along the eastern side of Trail Ridge before turning east to the Atlantic. Longtime residents of the Okefenokee Swamp, referred to as "Swampers", were of overwhelmingly English ancestry . Due to relative isolation, the inhabitants of the Okefenokee used Elizabethan phrases and syntax preserved since the early colonial period when such speech was common in England, well into the twentieth century. [ 1 ] The Suwanee Canal was dug across the swamp in the late nineteenth century in a failed attempt to drain the Okefenokee. After the company's bankruptcy, most of the swamp was purchased by the Hebard family of Philadelphia, who conducted extensive cypress logging operations from 1909 to 1927. Several other logging companies ran railroad lines into the swamp until 1942; some remnants remain visible crossing swamp waterways. On the west side of the swamp, at Billy's Island , logging equipment and other artifacts remain of a 1920s logging town of 600 residents. Most of the Okefenokee Swamp is included in the 403,000 acre (1630 km²) Okefenokee National Wildlife Refuge .