Rock from a borehole deep at Olkaria is around 450,000 years old., but the surface features are no more than 20,000 years old. The oldest exposed sequence is the Ol Njorowa pantellerite formation of pyroclastic rocks, lava flows and plugs. This is thought to be related to a caldera by that later collapsed but is indicated by traces of a ring fracture. The magma has a wide range of compositions representing the different phases after the caldera collapsed. Although dating is not precise, it seems that the older rocks date to 9,000 years before present, while the youngest rocks in the Olobutot formation are between 130 and 230 years old.