The geology of this area is diverse with a terrain resulting from three main groups of processes: volcanism, faulting and changes in sea level (Rosengren, 1986)[1]. These processes have created many features that make the region geologically significant including glacial material, deep gorges resulting from faulting, and lava flows and eruption points from volcanic activity.

Roughly 400-500 million years ago, the sea covered the area, allowing sand and mud to be deposited. After the sea withdrew, uplifting occurred, forming north-south running mountain ranges. This was followed by a long period of erosion. Approximately 250 million years ago, glaciers formed and as they moved over the land they exposed large granitic rocks. Rubble was deposited in the valleys and conglomerates and sandstone were deposited in the lakes and rivers that were created as the glaciers melted. These are some of the earliest glacial deposits known to exist in the world, adding to the geological significance of the Bacchus Marsh area (Lubczenko 1994)[2].

Following movements of the Rowsley Fault approximately 1-2 million years ago, deep gorges formed along the Werribee River, Lerderderg River and Parwan Creek. The youngest geological materials are alluvial and colluvial fan deposits and confined floodplain deposits. Sandy fans have been built along the Rowsley Fault escarpment and Greendale Fault and alluvial terraces have developed in the valleys of the Werribee and Lerderderg Rivers Rosengren 1986)[1] & (NRE Flora & Fauna Port Phillip Region 2002)[3].

[1] Rosengren, N. J. (1986)
Sites of Geological and Geomorphological Significance in the Western Region of Melbourne.
Prepared by the Department of Geography, University of Melbourne for the Department of Conservation, Forests and Lands, Victoria.
[2] Lubczenko, V. (1994)
From Land Despair to Landcare. ‘Reading the Land’ around Bacchus Marsh.
Department of Conservation and Natural Resources Victoria and the Geography Teachers’ Association of Victoria.
[3] NRE Flora & Fauna Port Phillip Region (2002)
A Strategy for conserving biodiversity in the Central Victorian