Togo is traversed in the center by a chain of hills, the Togo Mountains, extending roughly southwest into Ghana and northeastward into Benin and averaging about 700 m (2,300 ft) in height. The highest elevation is Mt. Agou (986 m/3,235 ft). To the north and west of these hills, the Oti River drains in a southwesterly direction into the Volta River, which constitutes a part of the upper boundary with Ghana. To the north of the Oti River Valley lies gently undulating savanna country. From the southern spurs of the central hills, a plateau stretches gradually southward to a coastal plain. The coastline consists of a flat sandy beach thickly planted with coconut trees and partially separated from the mainland by lagoons and lakes that are the former estuaries of several rivers.