Geology

Perth is pretty flat. The only hills we have on the Swan Coastal plain are the undulating hills that parallel the coastline which are actually million year old sand dunes. Many of Perth's swamps and lakes have formed within the dune system.

The Darling Scarp, also referred to as the Darling Range, is a low escarpment running north-south to the east of the Swan Coastal Plain and Perth, Western Australia. It extends generally north of Bindoon, to the south of Pemberton, and easterly to include Mount Bakewell near York and Mount Saddleback near Boddington. It started to form about 570 million years ago and is made of rock that is up to 3700 million years old, which is geologically very old. The western edge is called the Darling Scarp, and it rises steeply 200m+ from the Swan Coastal plain (It was a challenge for the early settlers to find a suitable route for getting trains up and down, and it took them 3 attempts to find the right route!). The top is called the Darling Plateau and it features vast, gently undulating jarrah covered hills and valleys that may rise to nearly 600m. The highest peaks are Mount Cooke (582m), Solus (574m) and Dale (546m). In the past 100 years, the Darling Scarp has been exploited for stone quarries, forestry and bauxite (rock containing metal aluminium) mining.

Laterite ( a red clay material that is hard when dry) covers much off the Darling Plateau. It consists of mottled soils overlain by duricrust, which is a hard red/brown cap that looks like cemented gravel. When it weathers it forms "pea gravel" , small ball like rocks that are very hard to ride through. Where laterite is aluminium rich it is called bauxite, and often mined.

The annual rainfall of the scarp varies from north to south from about 750 mm to 1400 mm. Most of it falls in the winter and soaks through the gravelly ground surface to the clays below. The Darling Scarp has been weathered by rain for many millions of years, so essential nutrients that are most likely to promote plant growth, have been leached out and are in short supply. Jarrah seedlings frequently germinate and grow after the occasional fire, on the ash-bed where the nitrates and phosphates are more readily available and competing understorey plants have been killed.

Often the Bureau of Meteorology identifies different weather for "the hills" in comparison to that of the Swan Coastal Plain. Also, in traditionally hot summers, strong easterly winds travelling across the scarp have presented serious issues for planes using the Perth Airport because of the alignment of the runways.A documented accident in 1999 involving wind shear from the scarp is at the Perth Airport article. In addition, orographic uplift is produced when rain clouds move over the hills, giving higher rainfalls in settlements in the ranges compared with their coastal neighbours.

This page is the property of Follow My Ride, a website detailing off road cycle tracks near Perth and in Western Australia.