Took this one on Fathers Day, on an afternoon with Dad and a few of the family...
Less than 20 million years ago, a series of volcanic flows covered parts of the Blue Mountains in a layer of basalt. Over the years, erosion has removed much of this layer, leaving the sandstone cliffs and valleys we are familiar with. However, in a few places where the basalt was thickest, it has remained, protecting the softer sandstone underneath from eroding.
Many of the well known peaks such as Mt Hay, Mt Tomah, Mt Wilson and Mt Irvine are basalt capped, and the more fertile soil supports quite a different community of plants than the sandstone.