It began as a separate block of the earthââ¬â¢s crust that collided with the east coast of Gondwanaland approximately 290 million years ago. About 247 million years ago (known as the late Permian, early Triassic), a series of massive volcanic eruptions occurred in the vicinity of Tenterfield and Deepwater. These eruptions were large enough to have a significant impact on the earthââ¬â¢s atmosphere and climate at the time. In other words the scale of the eruptions was phenomenal, orders of magnitude beyond any historical events. It would have contributed towards numerous extinctions of the then existing flora and fauna.A large mass of molten rock at depth became over pressurised and exploded through the overlying earthââ¬â¢s crust, possibly through several eruptive centres.A remarkably uniform rock called the Dundee Rhyodacite ignimbrite is the resulting evidence of this massive volcanic event. It was basically the super-heated volcanic ash that spread out across the terrain at high velocity and settled in a mass in excess of 2 kilometres thick over an area of 60 x 40 kilometres. The local term for this ignimbrite is ââ¬Ëblue graniteââ¬â¢ and it weathers to produce light sandy loam soils. Weathering and erosion have removed most of the original ignimbrite. Later geological activity resulted in resurgent intrusions such as Bluff Rock, followed by an extensive granite intrusions e.g. Mt Mackenzie, Doctors Nose and Girraween National Park.
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