evidence: Hainan Island was geologically connected with the southern Chinese mainland until a rift through the Hainan Strait opened sometime during the Miocene and Pliocene epochs (about 23 to 2.6 million years ago). The island is approximately oval in shape and measures about 160 miles (260 km) from east to west and 130 miles (210 km) from north to south at its widest point. The land rises abruptly in the southwestern interior of the island, reaching an elevation of 6,125 feet (1,867 metres) above sea level at Mount Wuzhi. Immediately to the northwest of the Wuzhi massif is the Limu Range, with several peaks above 4,600 feet (1,400 metres). Lower hills and tablelands fan out from this mountainous centre, culminating in narrow coastal alluvial plains that reach their broadest extent in the northeast. Dozens of rivers and streams cascade out of the mountains to the sea through tablelands and plains; the longest, the Nandu River, flows northeastward, while the other two major rivers, the Changhua and Wanquan, flow to the west and east, respectively, from the mountainous core. Hainan’s long coastline of more than 930 miles (1,500 km) contains numerous bays and natural harbours.