The area is defined by alternating ridges and valleys forming concentric rings, a geological formation that rises abruptly from the surrounding plains. The Pilanesberg is named for chief Pilane of the Kgafêla people, who ruled from Bogopane, Mmamodimokwana and eventually Mmasebudule during the 1800s. The 'Pilanesberg Alkaline Ring Complex' is the park's primary geological feature. This vast circular feature is geologically ancient, being the crater of a long-extinct volcano - the result of eruptions some 1,200 million years ago. It is one of the largest volcanic complexes of its type in the world, the rare rock types and formations make it a unique geological feature, and a number of rare minerals occur in the park.