Island O'ahu was born by volcanic eruptions from two shield volcanoes 2.5-3 millions years ago. After 2 millions years of volcanic inactivity, the southeastern end of Ko'olau Range erupted. This eruption created a rock called tuff cone of Diamond Head. Today's shape have created erosions during last 300 000 years. The southeastern rim is higher because winds were blowing ashes in this direction during the eruption.
Diamond Head was designated a National Natural Landmark in 1968. Hawaiians used to do here their ceremony.
The name Diamond Head mountain got by the end of 18th century when Western explorers and traders mistook the calcite crystal in the rocks on the slope of the crater for diamonds.
The summit of Diamond Head is an ideal site for costal defense of O'ahu. That's why was purchased by the Federal government and since 1904 has been by military. fortification began in 1908 with the tunnel construction in northern wall. Batteries however never has been used. At the same time was built at the summit Fire control station. To the summit is now public open trail long 1.3 kilometers with nice overlook over Honolulu. The monument is open daily till 6:00 pm. Entrance fee is $1. (2002)