Hiva Oa is the largest and most fertile of the islands in the southern group of the Marquesas Archipelago. It is located at 139° west longitude and 9°45’ south latitude. Hiva Oa has deep valleys, a lush plateau and dense forests. The island, which covers an area of 320 square kilometers (123.6 sq. miles), has a curious and complex geological structure. All that is left of the volcano Taaoa is a 1,000-meter (3,281-ft.) high wall, which is on the edge of a volcanic crater. The volcano Atuona formed inside that crater. Further evidence of former volcanic activity is a ridge that forms a spine across the entire length of Hiva Oa, from Atuona to the former volcano Puamau, broken up only by the dike of Mt. Otua, which reaches to a height of 924 meters (3,031 ft.). Atuona, the administrative center for the southern group of the Marquesas Islands, is 1,184 kilometers (736 miles) north of the island of Tahiti. Surrounded by the mountain on the land side and the Bay of Traitors on the ocean side, Atuona offers safe anchorage. But that anchorage area was abandoned by visiting sailboats and trading schooners after a port with a protective seawall was built in 1981 in the neighboring Tahauku Bay.