Tamborine Mountain’s ancient uprising is the result of eruptions from a huge shield volcano in the Mount Warning area of northern New South Wales about 20 to 23 million years ago. Eruptions smothered the surrounding landscape with layers of basalt lava flows. By the time the eruptions had ceased, this Tweed Volcano had risen to a height of 2 km and a diameter of about 100 km, forming a vast dome stretching south to Lismore, west to Mount Lindsay and north to Tamborine Mountain.