Although the Darling is one of the largest and most important of Australia’s river systems, there have been very few studies on the evolution and geomorphology of the catchment.
Geologically, the Darling catchment is a large saucer-shaped basin. The catchment dates back some 65 million years and has been constantly changing. Mountains have been uplifted and eroded, climates have changed, animal species have become prolific and then extinct. The oldest rocks in the Murray-Darling Basin are over 100 million years old and include the highly deformed rocks in the Broken Hill region, west of the Darling River.
Much of the Darling catchment is an ancient, weathered landscape resulting from millions of years of alteration. Many of the catchment’s river systems are likely to have originated about 140 million years ago, although the main Darling River is considered to be slightly older (when dinosaurs roamed the earth).
One of the many remarkable features of the Darling River is the relatively straight path it takes across the landscape. This path follows a series of complex faults that run from the north-east to the south-west. There are a series of smaller faults that cause the channel to change course abruptly, causing the river to appear in a ‘stepped’ pattern.
Sandy ridges are a notable feature of the Darling River floodplain. Although they are only small in elevation, they cover large areas of the landscape. They are believed to be the remnants of a system of streams that have a history very different to that of the current river channel, but they all reflect a history of on-going change in the landscape.
There are many lakes in the lower Darling region. Some are fossil lakes that are totally dry for most of the time, while others are seasonally-filled or partly-flooded. These lakes, such as the Menindee Lakes, were probably billabongs or floodplain depressions.