 The basalt and rhyolite lava that once flowed from the Tweed volcano (known as Mount Warning), which erupted over 23 million years ago, has produced various vegetation communities.On soil with a rhyolitic base is warm temperate rainforest that covers much of the park, and the nutrient rich basalt soil produces sub-tropical rainforest.Nightcap has the highest rainfall in NSW with rain exceeding 2500mm per annum.