Rocks from the renewed volcanism stage are also present but have not been dated. This volcano has been extensively modified by erosion. Koolau is a large basaltic volcano that makes the east side of the island. The main shield is about 2.7 to 1.8 million years old. A caldera is located just south of Kaneohe Bay, the prominent bay on the north side of the island.
Numerous dikes mark the location of a rift zone that trends to the northwest.
No rocks from the capping stage have been found on Koolau volcano. Much of Koolau volcano was also removed by a giant landslide .