The Park contains a range of significant geological and geomorphological features. About one million years ago, uplifting along the Rowsley fault caused down-cutting of the Lerderderg River. The resulting Lerderderg Gorge is an outstanding illustration of stream rejuvenation resulting from faulting (Rosengren 1988). Extensive sections of Lower Ordovician sediments are displayed throughout the gorge, and the more resistant sandstones form massive cliffs and rock bars.
The southern end of the gorge in particular is of international significance for the exposed rocks which show evidence of being covered by glaciers during the Permian, about 280 million years ago (Rosengren 1988). Rosengren (1988) recommended that outcrops and the southern end of the gorge in particular be protected.
The Park also contains examples of volcanic geological processes of the early Pleistocene period when Mount Blackwood and Mount Bullengarook spread olivine basalt over the plains and some valleys.
The steep slopes of the Park have shallow skeletal soils with fractured rock at the surface (O’Shea 1986). These soils have a high erosion potential, particularly if exposed through vegetation clearing.
The Ordovician duplex soils of Lerderderg State Park are highly dispensable, making them extremely susceptible to erosion (Soil Conservation Authority & Land Conservation Council 1975).
The removal of vegetation and development of tracks and roads encourages sheet, gully and tunnel erosion (DCE 1991).
Increase in sediment input into Victorian rivers and streams due to human activities is listed as a potentially threatening process under Schedule 3 of the Flora and Fauna Guarantee Act.
Conservation of the Lerderderg State Park aims to:
- Protect and maintain the natural, aesthetic and scientific values of significant geological and geomorphological features.
- Prevent and control soil erosion and to minimise soil disturbance during all activities.