The Hunter Region is considered a transitional area between the Paleozoic rock foundation of the New England Fold Belt located to the south and the Early Permian and Middle Triassic period rock formations of the Sydney Basin to the south. Between these two geological areas is the Hunter-Mooki Thrust fault. At one time this fault was very geologically active and gave rise to the Brokenback range that feature prominently in the Hunter region. Strips of basalt found throughout the region also bear witness to the volcanic activity that has occurred in the history of this fault.