The Ridge Hill Shelf is a landform that forms part of the foothills of the

Darling Scarp The Darling Scarp (), also referred to as the Darling Range or Darling Ranges, is a low escarpment running north–south to the east of the Swan Coastal Plain and Perth, Western Australia. The escarpment extends generally north of Bindoon, to ...

, a low escarpment that runs parallel with the west coast in southwest

Western Australia Western Australia (WA) is the westernmost state of Australia. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to the south, the Northern Territory to the north-east, and South Australia to the south-east. Western Aust ...

. It was formed by

coastal erosion Coastal erosion is the loss or displacement of land, or the long-term removal of sediment and rocks along the coastline due to the action of Wind wave, waves, Ocean current, currents, tides, wind-driven water, waterborne ice, or other impacts ...

of the scarp in the

Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

, when the sea level was higher, and the scarp located further west than at present. The action of coastal forces produced

sand dune A dune is a landform composed of wind- or water-driven sand. It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex. A large dune complex is called a dune field, while broad, flat ...

s that subsequently

lithified Lithification (from the Ancient Greek word ''lithos'' meaning 'rock' and the Latin-derived suffix ''-ific'') is the process in which sediments compact under pressure, expel connate fluids, and gradually become solid rock. Essentially, lithificati ...

into

eolianite Eolianite or aeolianite is any rock formed by the lithification of sediment deposited by aeolian processes; that is, the wind. In common use, however, the term refers specifically to the most common form of eolianite: coastal limestone consisting ...

, and eroded the

ironstone Ironstone is a sedimentary rock, either deposited directly as a ferruginous sediment or created by chemical replacement, that contains a substantial proportion of an iron ore compound from which iron (Fe) can be smelted commercially. Not to be c ...

of the scarp, resulting in an iron-rich sandstone with a

laterite Laterite is a soil type rich in iron and aluminium and is commonly considered to have formed in hot and wet tropical areas. Nearly all laterites are of rusty-red coloration, because of high iron oxide content. They develop by intensive and prolo ...

cap. The iron gives the sandstone a dull purple-brown colour; depending on the extent of iron-enrichment, the sandstone may appear predominantly yellow, predominantly purple-brown, or a mottled combination of the two. The shelf is about high on average, and is therefore well-drained. It is largely vegetated by a forest of ''

Eucalyptus marginata ''Eucalyptus marginata'', commonly known as jarrah, in Noongar language and historically as Swan River mahogany, is a plant in the Myrtus, myrtle Family (biology), family, Myrtaceae and is endemism, endemic to the Southwest Australia, south-we ...

'' (jarrah) and ''

Corymbia calophylla ''Corymbia calophylla'', commonly known as marri, is a species of flowering plant in the family Myrtaceae and is endemic to the southwest of Western Australia. It is a tree or Mallee (habit), mallee with rough bark on part or all of the trunk, ...

'' (marri), with an understorey of ''

Banksia ''Banksia'' is a genus of around 170 species of flowering plants in the family Proteaceae. These Australian wildflowers and popular garden plants are easily recognised by their characteristic flower spikes, and woody fruiting "cones" and head ...

'', '' Casuarina fraseriana'' and '' Xylomelum occidentale'' (woody pear).https://www.kalamunda.wa.gov.au/our-city/environment/flora-fauna/landforms Landforms of Kalamunda Some publications identify the Ridge Hill Shelf with the foothills of the scarp, but this is incorrect. The foothills are about 15 kilometres wide, and largely continuous, whereas the Ridge Hill Shelf is no more than 3 kilometres wide and highly discontinuous.

References

Further reading