The Puʻu Kukui summit area at the valley's head receives an average 386 inches (9.8 m) of rainfall per year,[4] making it the state's second wettest location after The Big Bog, slightly wetter than Mount Waiʻaleʻale.

Above the ʻĪao valley at the Puʻu Kukui watershed is a native cloud forest of ʻOhiʻa and Koa.

Maui's ruler Kakaʻe, in the late 15th century, designated ʻĪao Valley as an aliʻi burial ground.

In 1790, the Battle of Kepaniwai took place there, in which Kamehameha the Great defeated Kalanikūpule and the Maui army during his campaign to unify the islands.

Tributes and structures celebrate the contributions of Hawaiian, American missionary, Chinese, Japanese, Portuguese, Korean, and Filipino cultures.