The Hilo soil series consists of very deep, moderately well drained soils that formed in many layers of volcanic ash with lesser amounts of dust from the deserts of central Asia. These dust layers are noticeable because their gray color contrasts with the dark brown and dark reddish brown subsoil formed in volcanic ash. There are several buried layers within the Hilo soil profile. Hilo soils occur on the uplands of the Mauna Kea volcano along the Hāmākua Coast on the island of Hawaii.