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Reflections in Rocky Creek at Cranky Rock
Balancing rock on top of the formation
Boulder showing rock peeling off host rock
The suspension bridge at Rocky Creek Reserve

Cranky Rock Nature Reserve

Latitude -29.561048, Longitude 150.645497

Located in the New England Region of NSW, nearest town Warialda

Link to Detailed Map

The name Cranky Rock was derived from a local legend which said that an elderly "Cranky Chinaman" jumped to his death from the highest point of the balancing rocks after being accused of murder.

The traditional owners of the land at Cranky Rock Nature Reserve are the Kamilaroi people and there are many important indigenous heritage sites in the area. The reserve's most outstanding natural feature is an assembly of giant boulders, heaped into the most precarious positions, and then cut through by a creek leading to a crystal clear reflective pool.

Geology

The outcrop of boulders known as Cranky Rock is composed of Late Permian age Dumboy- Gragin Granite which is approximately 245 million years old. These boulders are called tors. What appears to be the stacking of boulders one atop another is actually the result of millions of years of weathering eroding the joints between slabs of rock, leaving rounded tors which will eventually topple.

Tors and Joints

Tors are rounded, block-like outcrops of rock (usually granite). They form in hard, massive granite which has cracked along vertical and horizontal fractures: these fractures are known as "joints". Vertical joints form as molten granite cools and contracts within the earth's crust. Some granites have abundant, closely-spaced (metres apart) joints, whereas others have very widely spaced (hundreds of metres apart) joints. Horizontal joints form as rock covering the granite is eroded away, reducing the mass of overlaying rock. This process is known as "unloading". Unloading results in the expansion of rocks nearing the earth's surface, which results in horizontal cracking. Then, as groundwater moves into the joints, it begins to react with the fresh minerals in the granite, causing the minerals to break down into other varieties, whilst the granite itself weakens and begins to exfoliate from the underlying fresh rock. Rinds of weathered granite wrapped about fresh granite may resemble the structure of an onion, giving rise to the term "onion skin weathering". As rinds peel off, rounded tors are left and when there is a horizontal fracture in the granite this can result in two tors stacked vertically as each independently weathers into the typically rounded shape.

This process can be accelerated by freeze-thaw conditions where water invades the joint line, then the temperature drops and freezes the water. Ice expands the original water's volume by 9% thus pushing the rocks on either side of the joint apart or breaking off pieces of rock to form scree slopes.

Facilities

The Cranky Rock Nature Reserve features excellent picnic facilities, barbecues, a suspension bridge, free roaming native birds and wildlife, walking tracks and a viewing platform. The camping area has power available, a kiosk and a bush shower facility.

Getting There

Cranky Rock Nature Reserve is located on Rocky Creek 7.5km east of Warialda in North Western NSW. Turn north off the Gwydir Highway to reach the reserve via an unsealed, sign posted road. Besides camping at the reserve there is also accommodation available in Warialda.

Photo showing joint plane

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