Nature, culture and history
Perched high above the head of the Pioneer Valley, Eungella National Park is the central part of the extensive plateau of the Clarke Range, extending from well north of Dalrymple Heights farming area, through Eungella township, to south of the Crediton locality. The eastern edge of the plateau is a spectacular escarpment.
The plateau is largely carved on hard granitic rocks resistant to erosion. Most were intruded into the Earth’s crust as molten bodies during an episode of crustal heating and mountain building in the late Carboniferous to early Permian periods (300–275 million years ago). Look for evidence of the granitic rocks on the slopes of the escarpment and in the riverbeds such as in the Broken River south of the national park visitor area (Granite Bend walking circuit).
Notice that the granitic rocks are not evident on the plateau surface. There, deep red soils over pale clays dominate the landscape. The plateau is believed to be an ancient, higher-level land surface, deeply weathered from the granite sometime between 35 and 15 million years ago and is now eroding around its edges. Its red soils have developed from iron and aluminium oxides accumulating in the soil surface profile and are more fertile than soils derived from granite. The rich red soils support the lush growth of rainforest in the high rainfall belt along the plateau’s eastern edge, as well as the farming which has taken place since the clearing of the plateau.
About 34 to 32 million years ago, basalt lavas on the plateau in the Crediton State Forest area were erupted from volcanoes to the south, near Homevale National Park.
Eroding Finch Hatton Gorge
The popular Finch Hatton Gorge sits well below the plateau surface and reveals rainforest growing on typical granite terrain. The gorge runs north-south due to the presence of strong fractures in the granite and an intrusion of black basalt. The stream finds it easier to erode the softer basalt and to pluck out blocks along lines of weakness in the granite. The creek is therefore trapped for much of its length in a narrow slot eroded into the basalt dyke. Some of the original granite formations are still in place, but most of the boulders you see in the gorge have careered down from the steep slopes above.
Geology adapted from content courtesy of Warwick Willmott.