The Focal Peak Volcano was centred to the west near the present Mount Barney about 24 million years ago. The much larger Tweed Volcano (centred over the present Mount Warning in New South Wales) erupted shortly afterwards about 23 million years ago, covering many of the lavas of the Focal Peak Volcano in the west as well as older rocks in the east. It built up a broad, gently sloping dome or shield of mainly basalt lavas, with one major interval of rhyolite (the Beechmont Basalt, succeeded by the Binna Burra Rhyolite and then the Hobwee Basalt). These lavas extended over the present border ranges to at least Tamborine Mountain in the north, Lismore in the south, and Mount Lindesay in the west. The central summit of the volcano is estimated to have reached about 2000m above sea level.
Source : http://qld.gsa.org.au/rockland_files/oreillys.pdf
The ridge of Green Mountains on which Reilly's is located and all the high country to the south are formed on some of the latest lavas from the Tweed Volcano, known as the Hobwee Basalt. The flat ridge crests approximate the original surface of the northern flank of the volcano. The best places to gain an appreciation of the volcanic mountain and its landscapes are at Python Rock and at Pats Bluff on the Western Cliff.
To claim a find for this Earthcache you will need to go to Python Rock and Pat's Bluff and answer the following questions:.
At Python Rock.
1. What type of rock is beneath your feet?.
2. As you look up Moran's Creek what has caused the feature you are looking at?.
Pat's Bluff .
3. Looking due South you now have a clear view of Lost World as well as Castle Craig which was in front of you at Python Rock. What types of lava created Castle Crag and the Lost World?.
4. Why do you think the Western Cliff line resisted erosion?.
Please email your answers to the cache owner when you submit your found it log..