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. The island is an important defense area that includes the headquarters of the U.S. Pacific Command and the Pearl Harbor naval base. Large pineapple and sugarcane plantations cover the rural areas of the island, and their products form Oahu's chief agricultural exports. Dairy farming and fishing are also important activities, but tourism is the principal economic mainstay of Oahu.