The You Yangs

The You Yangs are a series of low granite ridges rising up to 300 m (at Flinders Peak) above the Werribee Plains, about 50 km WSW of Melbourne. The main ridge runs roughly N-S for about 9 km, with a lower extension running for about 15 km to the west.

Granite outcrops on the eastern face of the You Yangs

Granite outcrops on the eastern face of the You Yangs
Photographer: Bill Birch. Source: Museum Victoria

Contrary to popular belief, the You Yangs are not the remains of a volcano. The granite that forms them was originally a mass of magma that had worked its way up into the surrounding sedimentary rocks during a period of geological time known as the Devonian, when the land surface in Victoria was several kilometres higher than today. The magma crystallised before it reached the surface, so it did not produce any volcanic activity. Instead, a very slow cooling rate allowed many large white crystals of feldspar to form. These can be seen in many of the granite outcrops throughout the ranges. In places the crystals appear to be lined up, probably because the sticky magma was still moving around when they were growing. The rock enclosing the big feldspar crystals mainly contains crystals of greyish quartz and two black minerals (hornblende and a variety of mica known as biotite).

There are also some tiny crystals of two minerals, allanite and titanite, that contain radioactive elements such as uranium and thorium. Titanite crystals have been used to calculate that the You Yangs granite solidified 365 million years ago. In many places in the granite there are dark grey clots and lumps. These are called ‘xenoliths’ and are pieces of sedimentary rock that have been caught up and baked by the magma.

The land surface has been lowered by erosion over the millions of years since the granite solidified, so it is now exposed. Because it is a hard rock, it has resisted erosion better than the rocks that surrounded it. The size and shape of the rounded tors are controlled by fractures in the granite that resulted from slight shrinkage during cooling. Weathering and erosion of the granite has formed a blanket of sandy soil that covers any contacts with surrounding rocks.

The You Yangs: View north from Flinders Peak

View north from Flinders Peak
Photographer: Bill Birch. Source: Museum Victoria

The young volcanoes

The countryside surrounding the granite ridges is a lava plain. Known as the Werribee Plain, it forms part of the vast Western District Volcanic Plains that extend from Melbourne to the South Australian border. Volcanoes began erupting lava flows about 4.5 million years ago, and the youngest eruptions are only about 10 000 years old. There are over 400 mapped craters and vents on the plains. While all these individual volcanoes are extinct, the volcanic field itself is only dormant, so that a new eruption is possible at any time.

The nearest volcanoes are the Anakies, the three low hills on the western horizon. These all have summit craters and provided lava flows for the plains south of the You Yangs. There were also flows from the low volcanoes of Bald Hill and Spring Hill to the north. 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.

Other geological features

The low wooded scarp along the western skyline is the Rowsley Fault, which has been active intermittently for millions of years. This fault is the western edge of a geological structure known as the Port Phillip Basin. Over millions of years, this basin has experienced periodic flooding by the sea, which is now represented by Port Phillip Bay. At a time of high sea level, perhaps a million years or so prior to the volcanic eruptions, the You Yangs would have been granite islands in a sparkling sea. Sands and gravels containing marine fossils occur along the southern edge of the granite ridges and mark the beaches and shorelines that formed at that time.

Geological Map of the You Yangs

Comments (47)

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Denis Fielding 12 November, 2009 07:49
I found this a really informative site for my teaching geology to my year 7 science class in geelong.
tnesha 3 March, 2010 18:29
was the youyangs a active volcanoe? plz get back to me
Discovery Centre 6 March, 2010 13:32

Hi Tnesha, thanks for your question.  As you will read above, the You Yangs are not the remains of a volcano, but rather a mass of magma that worked its way up into the surrounding sedimentary rocks.

John Jongsma 29 April, 2013 17:49
Please read the article, the answer lies within!!
Narelle 28 May, 2010 13:42
Hi My daughter has to do a project on creating an emergency plan for a natural disaster that we haven't had yet. She has chosen to do a volcanic eruption from a dormant volcano in Vic. Any info you could provide would be helpful.
Discovery Centre 29 May, 2010 12:36

Hi Narelle, perhaps consider searching the Geoscience Australia website for information about volcanoes and volcanic eruptions,

layla suto 1 June, 2010 18:00
are the you yangs being eroded by the rain and weather, i went there 4 a school excursion 2 weeks ago. because i need to know by june 18 2010 i need to do a progect about them being eroded...
Discovery Centre 3 June, 2010 10:23

Layla, yes, due to its nature as conglomerate rock, the substance that forms the You Yangs is slowly eroding over time as a result of natural causes. Hope this helps!

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Codie 21 August, 2010 14:32
Besides bone seed what are some of the main problems facing the You Yangs? Also who is responsible for caring for the You Yangs? Thanks
Discovery Centre 28 August, 2010 15:36

Hi Codie, the You Yangs faces a number of threats such as increased fire risk with drought conditions. Also being a small 'island' of vegetation in a largely cleared landscape it makes the You Yangs vulnerable to pest plant and animal invasion. This isolation from other areas of native vegetation means some species may not be able to recolonise if lost due to fire or other threats. The closeness of this park to Melbourne and its popularity with the public can also place pressures on the environment. Parks Victoria has more information about this park.

Rebecca 22 August, 2010 16:00
Hi i was just wondering what are the main Fauna and Flora at the You Yangs? Fauna: is it just mainly birds that live there, or are there others? Thanks :)
Discovery Centre 28 August, 2010 15:58

Hi Rebecca, Parks Victoria manage the You Yangs and the Parks Vic website gives more information about the flora and fauna of this park.

Zoe Barth 7 October, 2010 15:41
I would an aerial view of the you yangs to help with a school project plus other photos if possible
Discovery Centre 9 October, 2010 13:26
Hi Zoe - a search for "You Yangs" at PictureAustralia will find several images of the sort you are seeking! Best of luck with your assignment.
Ross 10 February, 2011 17:35
I have heard there is a cave (or possibly more than one) somewhere in the You Yangs ranges. If so, do you know anything about this? Thanks.
Discovery Centre 12 February, 2011 13:31
Hi Ross, we are not aware of any caves found in the You Yangs, but you might want to contact Parks Victoria who manage this reserve and will know for sure.
Peterjohn Walter 9 May, 2011 20:44
hi, I know the you yangs are currently closed due to the massive rainfall we had last summer, inwas wondering if you know if there is a time schedule for when it will open, specifically the mountain biking sections?
Discovery Centre 10 May, 2011 10:07

Hi Peterjohn,

Parks Victoria manage the You Yangs. If you go the Parks Victoria website, you will find more information.

Andy 25 May, 2011 16:25
Do you know how long the You Yangs extend?
Brooke 19 April, 2012 09:13
hey! can you please tell me who manages the you yang park? its really urgent for a really massive project! thankyou :)
Discovery Centre 19 April, 2012 13:04
Hi Brooke, if you have a look through the comments on this page, you will see your question has already been asked and answered. 
lewis 1 May, 2012 11:39
what was the you yangs environment like like before human settlement, after aboriginal settlement, after early european settelers, and in the 1900's compared to how they are now
olivia 1 May, 2012 11:43
what was the environment of the you yangs like before human settlement, after aboriginal settlement, after early european settlement and the 1900's compared to today