The Werribee Plain is an expansive low-lying flat land located between the northwestern shore of Port Phillip Bay and the Grampians Central Highlands of Victoria, Australia, shared between Melbourne and Geelong.
Named after the Werribee River, the plains are notable for their extensive, flat and rather featureless spans, interspersed by the occasional vertical feature, such as the You Yangs, a series of granite ridges and several small extinct volcanoes.
The granite that forms the You Yangs was originally a mass of magma that worked its way up into the surrounding sedimentary rocks during a period of geological time known as the Devonian.
Instead, a very slow cooling rate allowed many large white crystals of feldspar to form.
When these volcanoes were active, probably between 2 and 3 million years ago, the You Yangs would have been granite islands in a sea of lava.