The area known as Port Neches was once inhabited by tribes of the coastal-dwelling Karankawa and Atakapa Native Americans. Smith's Bluff (the future site of Sun Oil and Union Oil of California riverside property) and Grigsby's Bluff (now Port Neches) were the only two high land bluffs on the Neches River south of Beaumont. Before 1780, Grigsby's Bluff, specifically that part of Port Neches immediately east of Port Neches Park, had been a Native American town for at least 1,500 years, at first of the Karankawa tribe, whose skeletons were often found in the burial mounds there; and after 1650 of the Nacazils, a sub-tribe of the Attakapas, who were a short and stocky people before their extinction about 1780. As of 1841, there were six large burial mounds at Grigsby's Bluff, size about wide, tall, and long, consisting entirely of clam and sea shells, skeletons, pottery shards, and other Native American artifacts. Between 1841 and 1901, all six of the mounds disappeared, a result of human actions. Grigsby's Bluff became a post office in 1859 (there was also a store and sawmill there), but the office was discontinued in 1893.