Murrumbidgee - Ginninderra Gorges National Park

Landscapes and weathering

Doug Finlayson

Over the last 350 million years the Yass-Canberra region has been in a non-marine environment and erosion has exposed rocks at the surface that were once deeply buried. More recently, during the cool periods of the last 3 million years, there was extensive erosion of steep hillsides by rain and frost action. The net result is the gently rolling landscapes seen across the area of the proposed Murrumbidgee - Ginninderra Gorges National Park with deep river gorges cut through the softer rocks to form rapids, gorges and waterfalls.

Ginninderra Porphyry

Other consequences include the layers of sand, gravel and silt being deposited on the gently-sloping areas adjacent to the hillsides. Examples are seen along the Murrumbidgee River and its tributaries. Such near-surface deposits form the regolith the term applied to the blanket of weathered rocks and soils that cover the bedrock, often to depths of many metres.

Ginninderra Porphyry gravel quarried near Ginninderra Falls for use in landscape gardening. Similar deposits are found elsewhere in the region.


Drainage and river flow

Geology


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