Oahu ōäˈho͞o [key], island (1990 pop. 836,231), 593 sq mi (1,536 sq km), third largest and chief island of Hawaii, part of Honolulu co., between Molokai and Kauai. Oahu is composed of two parallel mountain ranges (Waianae and Koolau) that are separated by a rolling plain dissected by deep gorges. Mt. Kaala (4,040 ft/1,231 m) is the island's highest peak. Oahu has no active volcanoes, but there are many extinct craters, among them Diamond Head, Koko Head, and Punchbowl. Pearl Harbor indents the island's southern coast. Honolulu, the state capital and the economic center of Hawaii, is on the highly urbanized southern coast of Oahu. Manoa Valley is the site of the Univ. of Hawaii, Punahou Academy, and the Mid-Pacific Institute. The island is an important defense area that includes the headquarters of the U.S. Pacific Command and the Pearl Harbor naval base. There are many bathing beaches (including Waikiki), some of which have coral gardens. The large pineapple and sugarcane plantations that once dominated in rural areas of the island have closed down. Agriculture and fishing are important activities, but tourism is the economic mainstay of Oahu.

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