Besides the main Waimanu Stream, it includes Waihīlau Falls on a tributary.
The Waimanu Stream watershed includes many smaller flows from Kohala Mountain to the Pacific Ocean at sea level.
[3] A system of dikes of hard lava rock force large amounts of ground water dropped from the tradewinds into this valley, making it very different from the smaller shallow valleys directly to the west.
[4] This ridge is administered as the Puʻu O ʻUmi Natural State Area Reserve.
Waihīlau Falls is one of the tallest single drops of a waterfall in the United States.