Oido (Korean: 오이도; Hanja: 烏耳島) is an island on the West Coast region of South Korea's Gyeonggi Province (also known as Gyeonggi-do). It is an area of Siheung stretching from north to south with low hills under 72.9 m (239 ft).Oido has shell moundsthroughout the whole area, with the largest of the mounds located on the West Coast. The Oido shell mounds are the only remains of the exchanges between the North and South Neolithic cultures of the Korean Peninsula. The mounds also provide information on the Neolithic area's changing coastal environment.