The parent material and underlying rock types are an important factor influencing soils in the Sydney region. In the lower reaches of Whites Creek catchment Hawkesbury Sandstone is the dominant geological formation and the upper catchment is dominated by Wianamatta Shales. The original vegetation was dry sclerophyll open forests and eucalypt woodlands on sandstone formations and eucalypt woodlands and wet sclerophyll tall open forest on shales.
The soils surrounding Whites Creek, often show no resemblance to natural soils and are often young, formed on cut or fill.
Soil types change quickly over small distances on steep valley slopes. Soils are shallow on hill tops and deeper in the valley floors. Sandstone soils are shallow and sandy while soils formed on shales often have deep clayey subsoils.
Creeks formed on Hawksbury Sandstones are mainly in steep rocky valleys with rapids, waterfalls, rock pools and hanging swamps and they seldom meander in flood plains. Many undisterbed examples are found on the upper North Shore, especialy in Lane Cove River Valley. Hanging swamps in the Blue Maountains are well known as a permanent source of fresh, clean water in the headwaters of mountain streams. The artificial Whites Creek Wetlands attempts to mimic these natural swamps.
The topography formed on Wianamatta Shales is mainly undulating hills and the creeks have a gentle grade and meanders may form flood plains.
The upper reaches of Whites Creek flows gently through Wianamatta Shale. The grade increases when the creek flows into a deep steep sided valley of Hawkesbury Sandstone. The estuary is mangrove mudflats at the edge of Sydney Harbour.
In the lower portion of the catchment, Whites Creek flows through a valley with steep slopes and sandstone rock outcrops.
Hawkesbury Sandstone was formed early in the middle Triassic geological period about 225 million years ago and is dominated by coarse-grained, quartz sandstone rocks with minor shale lenses. This geological formation is common in the Mountains west of Sydney, extending from Moss Vale in the south including the Blue Mountains and north to the Goulburn River near Denman in the Upper Hunter Valley. Close to Sydney this formation is found throughout the Hornsby Plateau and along the foreshores of Sydney Harbour, Parramatta and Georges Rivers.
The valley surrounding the wetland is predominantly sandstone with sandy, shallow soils.
Yellow Earths and Earthy Sands are found on crests.
Siliceous Sands and Leached Sands found along drainage Lines.
Lithosols are shallow soils found in rocky areas.
Podzolic soils form on shale lenses.
These soils are typically sandy and shallow, with grey topsoil and yellow or light grey sand to sandy clay subsoil which may be very stony. Clay content gradually increases with depth and there is no distinct boundary between topsoil and subsoil. Slightly acid to neutral, these sandy soils are shallow, permeable and very infertile.
In the upper portions of the catchment a gently undulating landscape forms on Wianamatta Shales.
The Wianamatta geological group was formed late in the middle Triassic geological period after the Hawkesbury group was formed and the Wianamatta rocks lie on top of the Hawkesbury Sandstone rocks. The Cumberland plain in western Sydney is dominated by Wianamatta Shales.
Soils formed on shale generally contain more clay and are deeper than sandstone soils.
Podzolic soils are acid throughout and have a clear boundary between the topsoil and subsoil. The topsoils are loams with a brownish grey colour. The lower part of the topsoil has a pale light colour and may be bleached with a nearly white, light grey colour (bleached A2 horizon).
The subsoils are clayey and may be very deep. The colour of the subsoil can be red, brown or yellow and mottling may occur with a mixture of red, yellow and grey patches.
Red and Brown Podzolic soils are found in well-drained areas on crests and upper slopes. Yellow Podzolics are found on lower slopes in areas of poor drainage. The fertility of these soils is low and drainage poor.
Deposits of quaternary alluvium exist along the lower reaches of Whites Creek.
Large deposits of recently deposited sand are found in the eastern suburbs, especially from Centennial Park south to Botany Bay. These marine sands extend westward to Redfern, Alexandria and the Airport site. This area has many low lying areas with lakes and swamps. Early Sydney obtained its water supply from the Botany swamps.
Deep under Sydney there is a coal seam. Near Newcastle and Wollongong the coal seam is close to the surface and is easy to mine. Coal was mined in Balmain between 1897 and 1931. The mine head was next to the Birchgrove Public School and the mine shafts extended under Sydney Harbour. The mine was about 900 metres deep. It was difficult to mine the coal, water continually seeped into the mine and deep mines are difficult to operate. The mine is now completely sealed to prevent mine gases escaping to the surface.
Many early buildings in Sydney are constructed from sandstone. Often sandstone quarries simply existed when it was needed to excavate rock from a site for infrastructure including roads, shipping wharves and railway lines. Leichhardt Council owned a quarry in Moore Street where rock was won for many purposes including kerb and guttering.
Many brick pits existed on Wianamatta shales in the Sydney area. In the inner suburbs these pits are now closed down. The St Peters pit and the Homebush Bay pit in Olympic Park are two large, well known, old, closed pits. In early colonial Sydney bricks were made at Brickfield Hill, near Liverpool Street.
All of the original native vegetation in the catchment is cleared and the catchment is now densely built upon. The original vegetation was greatly influenced by the geology and soil types.
Dry sclerophyll woodland and open forest occurs on Hawkesbury Sandstone including Sydney Sandstone Ridgetop Woodland and Gully Forest. Red bloodwood, yellow bloodwood, scribbly gum, brown stringybark and old man banksia grow on the ridges and black ash, Sydney peppermint and smooth-barked apple on sheltered slopes. Wet sclerophyll tall open forest and dry sclerophyll open woodland occur on Wianamatta Shales including Turpentine, Ironbark Forest. Turpentine, White Stringybark, Red Mahogany and Grey Ironbark grow on the clay soils.
Estuarine Complex occurs on the Quaternary alluvium found along the lower reaches of the creek where it enters Sydney Harbour.
Rainforest plants existed in the moist, sheltered, sandstone gully of lower Whites Creek, and at the mouth of the creek, salt marshes and mangrove swamps occurred in the tidal zone of Rozelle Bay.
Coastal Sandstone Heath occurred on the rugged sandstone outcrops of the harbour with Swamp Woodlands in the lower lying areas.