Kohala had two active rift zones, a characteristic common to Hawaiian volcanoes. The double ridge, shaped axially, was active in both the shield and postshield stages. The southeast rift zone passes under the nearby Mauna Kea and reappears further southeast in the Hilo Ridge, as indicated by the relationship between collected lava samples. In addition, the two features align to one another more closely then does the ridge to Mauna Kea, of which it was once thought to constitute a part. The bulk of the ridge is built of volcanic rock with reverse magnetic polarity, evidence that the volcano is at least 780,000 years old. Older lava dated from the toe of the ridge was estimated to be roughly between 1.1 and 1.2 million years old.