valley, Maui county, northwestern Maui island, Hawaii, U.S. Situated on the eastern slope of Puu Kukui Mountain, it lies just north of Wailuku. Formed by erosion of the caldera whose volcano created the island's western peninsula, Iao Valley comprises a deep, narrow gorge 5 miles (8 km) long and flanked by heavily forested walls almost a mile high. Iao Needle, a volcanic monolith 2,250 feet (686 metres) high, soars nearly straight up from the valley floor. A 6-acre (2.5-hectare) section of the valley featuring the Iao Needle is designated a state park and a national natural landmark. A bronze tablet at the base of the feature commemorates the bloody 1790 battle of Kepaniwai (meaning “Dammed Stream,” referring to the blockage of the torrent by the bodies of Maui warriors), which added Maui to the kingdom of Kamehameha I.